Long-range electronic connection in picket-fence like ferrocene–porphyrin derivatives

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Long-Range Electronic Connection in Picket-Fence like Ferrocene-

Porphyrin Derivatives†

Charles H. Devillers,a Anne Milet,

b Jean-Claude Moutet,

b Jacques Pécaut,

c Guy Royal,

b Eric Saint-Aman

b

and Christophe Bucherb*

Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X 5

DOI: 10.1039/b000000x

The effects of a direct connection between ferrocene and porphyrin units have been thoroughly

investigated by electrochemical and spectroscopic methods. These data not only reveal that substitution of

the porphyrin macrocycle by one, two, three or four ferrocenyl groups strongly affects the electronic

properties of the porphyrin and ferrocenyl moieties, they also clearly demonstrate that the metallocene 10

centres are “connected” through the porphyrin-based electronic network. The dynamic properties of

selected ferrocene-porphyrin conjugates have been investigated by VT NMR and metadynamic

calculations. 1,3-dithiolanyl protecting groups have been introduced on the upper rings of the ferrocene

fragments to allow a straightforward and easy access to redox active picket-fence porphyrins. X-ray

diffraction analyses of the zinc(II) 5-[1’-[2-(1,3-dithiolanyl)]ferrocenyl]-10,15,20-tri(p-tolyl)porphyrin 15

and 5,15-bis[1’-[2-(1,3-dithiolanyl)]ferrocenyl]-10,20-bis(p-tolyl)porphyrin complex reveal the existence

of S-Zn bonds involved in supramolecular arrays. The solid state analysis of the trans-5,15-di-(1’-

(formyl)ferrocenyl)-10,20-di-(p-tolyl)-porphyrinatozinc(II) complex, obtained by deprotection of the

dithiolane substituted analog, is conversely found in the crystal lattice as a monomer exibiting an

hexacoordinated zinc metal centre.20

Introduction

Ferrocene and porphyrin have already been associated in a wide

range of molecular architectures to reach quite different

objectives. Our group has recently published a comprehensive

review on this topic.1 Their donor-acceptor properties have for 25

instance been exploited to investigate photoinduced electron

transfer processes and to mimic photosynthesis active sites. Such

molecular architectures containing multiple redox active centres

are also of fundamental importance for the development of

molecular devices for uses in analysis or in electronics.2,3 Their 30

ability to reversibly accept and/or release electrons at distinct

potentials is particularly promising in the context of molecular

electronics as each redox states can be considered as an elemental

data storage.3,4 Recently, much efforts have been devoted to

conjugated systems featuring several metallocenes directly 35

connected to, or fused with, a -conjugated porphyrin, notably to

enable an optimized “communication“ between metallocenes or

between the metallocene and the macrocycle.5-7,8-14 As a general

statement, the intramolecular “communication” between mutiple

redox centres within molecules might occur through bonds in 40

conjugated structures, or through space as a result of the

electrostatic repulsion between electrogenerated charges. The

magnitude of these phenomena mainly depends on a combination

of structural factors (distances, geometry) as well as on the

dielectric constant of the medium used for investigation.15,16 In 45

mixed-valence chemistry, the interaction is usually characterized

by the Vab parameter16 related to the coupling between metal-

centred orbitals and estimated from the characteristics of the

intervalence transition observed in the near IR spectrum. The 50

interaction between two chemically equivalent redox centres

exhibiting discrete Nernstian electron transfers can also be

revealed by simple electrochemical measurements, for instance

through the observation of two successive CV waves with

disctinct half-wave potential values (E1/2). As a matter of fact, the 55

Vab and E1/2 values depend on the same parameters and usually

exhibit parallel variations,16,17 although electrochemical

measurements simultaneously involve homovalent and mixed-

valence species produced transitorily at the electrode interface.

We now wish to report the synthesis and characterization of such 60

derivatives showing up to four ferrocene subunits introduced at

the meso positions of an aromatic porphyrin skeleton (Scheme 1).

Dithiolanyl protecting groups have been introduced on the upper

cyclopentadiene rings to enable further functionnalizations of the

metallocene-based picket fences surrounding the porphyrin core. 65

This article also reports on the determination of the wave splitting

(E1/2) observed in the electrochemical signature of poly-

ferrocenyl-porphyrin conjugates. We also report numerous

experimental evidences supporting the existence of efficient

electronic “communications” occuring between multiple 70

chemically-equivalent redox centres.

2 | Journal Name, [year], [vol], 00–00 This journal is © The Royal Society of Chemistry [year]

Experimental

Reagents and Instrumentation

Dichloromethane and dimethylformamide (Rathburn, HPLC

grade) have been distilled over calcium hydride under argon and

under reduced pressure over 3Å molecular sieves, respectively. 5

Electrochemical experiments were conducted in a conventional

three-electrode cell under an argon atmosphere at 20 °C using a

CHI 660B electrochemical workstation. The working electrode

was a vitreous carbon disc (3 mm in diameter) polished with 1

µm diamond paste before each record. The non aqueous Ag/Ag+ 10

reference electrode was purchased from CH instrument, Inc. (10

mM AgNO3 in CH3CN containing 0.1 M tetra-n-butylammonium

perchlorate (TBAP)). Under these experimental conditions, the

potential of the decamethylferrocene/ decamethylferrocenium

(DMFc/DMFc+) redox couple, used as internal reference in 15

dichloromethane and dimethylformamide, was observed at E1/2 =

–345 mV and –410 mV, respectively.add footnote : In these

conditions (DCM/TBAP), we found that E1/2[Fc/Fc+] =

E1/2[DMFc/DMFc+] + 0.545 V Rotating disc electrode (RDE)

voltammetry was carried out at a rotation rate of 600 rpm. Cyclic 20

voltammetry (CV) curves were recorded at a scan rate of 0.1 V s–

1. Electrolyses were performed at controlled potential using a Pt

plate (2 cm2). Electrochemical simulations and best fitting of

experimental data were performed by the Digisim software (vs.

3). High resolution mass spectra (HRMS) were recorded on a 25

MicrOTOF Q Bruker instrument in ESI (positive mode) or on a

Bruker Daltonics Ultraflex II spectrometer in the MALDI/TOF

reflectron mode with dithranol as matrix and polyethylene glycol

ion series as internal calibrant, at the Plateforme d’Analyse

Chimique et de Synthèse Moléculaire de l’Université de 30

Bourgogne (PACSMUB). NMR spectra were recorded on a

Bruker AC-2000 250 MHz. 1H chemical shifts (ppm) were

referenced to residual solvent peaks. UV-vis spectra were

recorded on a Varian Cary 100 spectrophotometer using quartz

cells. 35

Synthesis

1-[2-(1,3-dithiolanyl)]-1’-formylferrocene (1).

1,2-dithioethane (5.40 mL, 64.2 mmol) was added to a cold (0°C)

CH2Cl2 solution (450 mL) of 1,1’ diformylferrocene18 (15.9 g,

64.2 mmol). Trifluoroboride etherate (15.92 mL, 129.4 mmol) 40

dissolved in 160 mL of CH2Cl2 was then added dropwise (30

min.) at 0 °C. After stirring the resulting solution at 0 °C for 5 h,

an aqueous NaHCO3 solution (50 mL, 10 %) was added. The

organic layer was then washed with 100 mL of an aqueous

solution saturated with sodium bicarbonate, with 2×100 mL of 45

water and finally with 100 mL of brine. The organic layer was

then dried over anhydrous sodium sulphate, filtered and the

solvent was evaporated under reduced pressure. The crude

compound was purified by column chromatography on silica gel

using n-hexane, with increasing amount of ethyl acetate (0 to 2 50

%), as the eluent to afford 14.3 g (yield: 70 %) of pure 1-[2-(1,3-

dithiolanyl)-1’-formylferrocene isolated as a red solid.

NMR 1H (250 MHz, CDCl3, 298 K) (ppm): 3.30 (m, 4H,

thioethane); 4.27 (s, 2H, -Fc); 4.40 (s, 2H, -Fc); 4.61 (s, 2H, -Fc);

4.78 (s, 2H, -Fc); 5.42 (s, 1H, -HC(S-)2); 9.66 (s, 1H, -CHO). 55

These data are consistent with those reported in reference [19].

5-[1’-[2-(1,3-dithiolanyl)]ferrocenyl]-10,15,20-tri(p-tolyl)-

porphyrin (2H2); 5,10-bis[1’-[2-(1,3-dithiolanyl)]ferrocenyl]-15,20-di(p-tolyl)porphyrin (3H2); 5,15-bis[1’-[2-(1,3-dithio 60

lanyl)]ferrocenyl]-10,20-bi(p-tolyl)porphyrin (4H2); 5,10,15-

tris[1’-[2-(1,3-dithiolanyl)]ferrocenyl]-20-(p-tolyl)porphyrin (5H2).

5-tolyldipyrromethane20 (1.84 g, 7.8 mmol) and 1 (2.50 g, 7.8

mmol) were dissolved in 400 mL of anhydrous CH2Cl2 and 65

Argon was bubbled through the solution for about 15 minutes.

After protecting the mixture from light, trifluororacetic acid (0.60

mL, 7.8 mmol) was added dropwise. The solution was stirred at

room temperature for an additional period of 30 minutes and

neutralized with 2,4,6-trimethylpyridine (1.04 mL, 7.8 mmol). p-70

chloranil (1.92 g, 7.8 mmol) was then added and the mixture was

kept under stirring at room temperature for 3 h. The solvent was

evaporated under reduced pressure. The resulting crude oil was

suspended in 500 mL of a NaOH (2M) aqueous solution and the

mixture was stirred for 1 h at room temperature. The dark 75

precipitate was filtered off, washed with water and dried under

vacuum. The crude compound was purified by chromatography

on silica gel using CH2Cl2/n-hexane (75/25 v/v) as the eluent.

Four successive fractions were collected when increasing

amounts of ethyl acetate (0 to 2%) were added in the eluent to 80

give 2H2 (340 mg, 10 %), 4H2 (541 mg, 13%), 3H2 (240 mg, 6%)

and 5H2 (45 mg, 1%) isolated as dark green solids.

2H2: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): -2.31 (s, 2H, -

NH); 2.69 (s, 3H, -Me); 2.71 (s, 6H, -Me); 3.05 - 3.40 (m, 4H, -

S(CH2)2S-); 4.09 (m, 2H, -Fc); 4.36 (m, 2H, -Fc); 4.88 (m, 2H, -85

Fc); 5.51 (s, 1H, -HC(S-)2); 5.57 (m, 2H, -Fc); 7.55 (m, 6H, -

Tol); 8.09 (m, 6H, -Tol); 8.80 (m, 6H, -pyrr); 9.94 (d, 3J = 5.00

Hz, 2H, -pyrr). UV-vis. (CH2Cl2) λmax, nm (ε, L mol–1 cm–1):

422 (331000); 510 (10800); 588 (9200); 671 (8300). HRMS

(ESI/TOF) m/z calcd for C54H45N4FeS2: 869.2431; found: 90

869.2450 [M+H]+.


NH); 2.70 (s, 6H, -Me); 3.08 – 3.36 (m, 8H, -S(CH2)2S-); 3.99

(m, 4H, -Fc); 4.31 (m, 4H, -Fc); 4.87 (m, 4H, -Fc); 5.48 (s, 2H, -

HC(S-)2); 5.52 (m, 4H, -Fc); 7.54 (d, 3J = 7.25 Hz, 4H, -Tol); 95

8.05 (d, 3J = 8.25 Hz, 4H, -Tol); 8.68 (s, 2H, -pyrr); 8.74 (d, 3J =

4.75 Hz, 2H, -pyrr); 9.80 (s, 2H, -pyrr); 9.85 (d, 3J = 5.00 Hz,

2H, -pyrr). UV-vis. (CH2Cl2) λmax, nm (ε, L mol–1 cm–1): 427

(237000); 616 (12500); 692 (10400). HRMS (ESI/TOF) m/z

calcd for C60H51N4Fe2S4: 1067.1693; found: 1067.1696 [M+H]+. 100


NH); 2.71 (s, 6H, -Me); 3.06 – 3.36 (m, 8H, -S(CH2)2S-); 4.01

(m, 4H, -Fc); 4.31 (m, 4H, -Fc); 4.86 (m, 4H, -Fc); 5.48 (s, 2H, -

HC(S-)2); 5.52 (m, 4H, -Fc); 7.55 (d, 3J = 8.25 Hz, 4H, -Tol);

8.06 (d, 3J = 7.50 Hz, 4H, -Tol); 8.69 (d, 3J = 4.75 Hz, 4H, -105

pyrr); 9.78 (d, 3J = 5.00 Hz, 4H, -pyrr). UV-vis. (CH2Cl2) λmax,

nm (ε, L mol–1 cm–1): 425 (247000); 615 (13700); 695 (14200).

HRMS (ESI/TOF) m/z calcd for C60H51N4Fe2S4: 1067.1693;

found: 1067.1736 [M+H]+.

5H2: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): -1.14 (s, 2H, -110

NH); 2.69 (s, 4H, -Me); 3.06 – 3.36 (m, 12H, -S(CH2)2S-); 3.89

(m, 6H, -Fc); 4.25 (m, 6H, -Fc); 4.84 (m, 6H, -Fc); 5.42 (s, 3H, -

HC(S-)2); 5.44 (m, 6H, -Fc); 7.54 (d, 3J = 8.50 Hz, 2H, -Tol);

8.01 (d, 3J = 8.75 Hz, 2H, -Tol); 8.61 (d, 3J = 5.00 Hz, 2H, -

pyrr); 9.61 (d, 3J = 3.75 Hz, 4H, -pyrr); 9.74 (s, 4H, -pyrr). 115

UV-vis. (CH2Cl2) λmax, nm (ε, L mol–1 cm–1): 430 (187000); 635

This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00 | 3

(14700); 711 (12900). HRMS (ESI/TOF) m/z calcd for

C66H57N4Fe3S6: 1265.0957; found: 1265.0990 [M+H]+.

5,10,15,20-tetra[1’-[2-(1,3-dithiolanyl)]ferrocenyl]porphyrin

(6H2).

1-[2-(1,3-dithiolanyl)-1’-formylferrocene (1) (700 mg, 2.2 mmol) 5

and pyrrole (150 L, 2.2 mmol) were dissolved in 200 mL of

anhydrous CH2Cl2 and argon was bubbled through the solution

for about 15 minutes. After protecting the mixture from light,

trifluororacetic acid (250 L, 7.8 mmol) was added dropwise.

The solution was kept under stirring at room temperature for 2 h. 10

p-Chloranil (810 mg, 3.3 mmol) and triethylamine (460 L, 3.3

mmol) were then added. After stirring the resulting solution at

room temperature for 4 h, the solvent was evaporated under

reduced pressure. The crude compound was purified by column

chromatography on silica gel using CH2Cl2 as the eluent to give 15

240 mg (29 %) of 6H2 isolated as a violet solid.


NH); 3.02 – 3.38 (m, 16H, -S(CH2)2S-); 3.80 (m, 8H, -Fc); 4.19

(m, 8H, -Fc); 4.81 (m, 8H, -Fc); 5.34 (m, 8H, -Fc); 5.40 (s, 4H, -

HC(S-)2); 9.57 (s, 8H, -pyrr). UV-vis. (CH2Cl2) λmax, nm (ε, L 20

mol–1 cm–1): 435 (144000); 663 (15000); 726 (12800). HRMS

(ESI/TOF) m/z calcd for C72H63N4Fe4S8: 1463.0221; found:

1463.0224 [M+H]+.

5-(1’-(formyl)ferrocenyl)-10,15,20-tri(p-tolyl)porphyrin (7H2).

A solution of 2H2 (50 mg, 0.057 mmol) in THF (100 mL) was 25

added to a mixture of N-chlorosuccinimide (45.7 mg, 0.34 mmol)

and AgNO3 (58.1 mg, 0.34 mmol) dissolved in CH3CN/H2O (35

mL, 85/15, v/v). After stirring the resulting solution at room

temperature for 10 min., 1 mL of an aqueous solution saturated

with Na2SO3, 1 mL of an aqueous solution saturated with Na2CO3 30

and 1 mL of an aqueous solution saturated with NaCl were

successively added to the mixture. 50 mL of CH2Cl2 were then

added and the mixture was filtered. The filtrate was washed with

CH2Cl2. The organic phases were collected, washed with water

and dried over anhydrous Na2SO4. The black crude product 35

obtained upon evaporation of the solvent under reduced pressure

was purified by column chromatography on silica gel using

CH2Cl2 as the eluent to afford 32 mg (70 %) of 7H2 isolated as a

violet solid. 1H NMR and MS analyses of 7H2 are consistent with

those reported in reference [6]. 40

5,15-di(1’-(formyl)ferrocenyl)-10,20-di(p-tolyl)porphyrin

(8H2).

A solution of 4H2 (100 mg, 0.094 mmol) in THF (100 mL) was

added to a mixture of N-chlorosuccinimide (150 mg, 1.1 mmol)

and AgNO3 (191 mg, 1.1 mmol) dissolved in CH3CN/H2O (70 45

mL, 85/15 v/v). After stirring the resulting solution at room

temperature for 10 min., 2 mL of an aqueous solution saturated

with NaSO3, 2 mL of an aqueous solution saturated with Na2CO3

and 2 mL of an aqueous solution saturated with NaCl were

successively added to the mixture. 100 mL of CH2Cl2 were then 50

added and the mixture was filtered. The filtrate was washed with

CH2Cl2. The organic phases were collected, washed with water

and dried over anhydrous Na2SO4. The black crude product

obtained upon evaporation of the solvent under reduced pressure

was purified by column chromatography on silica gel using 55

CH2Cl2 as the eluent to yield 43 mg (50%) of 8H2 isolated as a

violet solid.


NH); 2.72 (s, 6H, -Me); 4.38 (m, 4H, -Fc); 4.80 (m, 4H, -Fc);

4.92 (m, 4H, -Fc); 5.57 (m, 4H, -Fc); 7.57 (d, 3J = 7.50 Hz, 4H, -60

Tol); 8.04 (d, 3J = 7.00 Hz, 4H, -Tol); 8.73 (d, 3J = 4,75 Hz, 4H,

-pyrr); 9.69 (d, 3J = 4.50 Hz, 4H, -pyrr); 9.89 (s, 2H, -CHO).

Mass spectroscopy (FAB+–MS), m/z: [M+1]+ = 915. HRMS

(ESI/TOF) m/z calcd for C56H42O2N4Fe2Na: 937.1902; found:

937.1921 [M+Na]+. 65

5-ferrocenyl-10,15,20-tri(p-tolyl)porphyrin (9H2).

Argon was bubbled for 15 minutes through a solution of 5-

tolyldipyrromethane (1 g, 4.23 mmol) and 1-carboxaldehyde-

ferrocene (905 mg, 4.23 mmol) in anhydrous CH2Cl2 (200 mL).

After protecting the mixture from light, trifluororacetic acid (0.47 70

mL, 6.3 mmol) was slowly added. The solution was kept under

stirring at room temperature for 30 min. and neutralized with

triethylamine (0.88 mL, 6.3 mmol). p-Chloranil (1.549 g, 6.3

mmol) was then added. After stirring for 3 h, the solvent was

removed under reduced pressure. The resulting crude oil was then 75

suspended in 500 mL of aqueous NaOH (2M) and the mixture

was stirred for 1 h at room temperature. The black precipitate was

filtered off, washed with water and dried. After evaporation of the

solvent, the resulting solid was purified by column

chromatography on silica gel using CH2Cl2/n-hexane (75/25 v/v) 80

as the eluent. The first fraction collected was the targeted 5-

ferrocenyl-10,15,20-tri(p-tolyl)porphyrin 9H2 (90 mg, 5.5 %).


NH); 2.69 (s, 3H, -Me); 2.71 (s, 6H, -Me); 4.18 (m, 5H, -Fc);

4.82 (m, 2H, -Fc); 5.55 (m, 2H, -Fc); 7.51-7.60 (m, 6H, -Tol); 85

8.05-8.13 (m, 6H, -Tol); 8.82-8.74 (m, 6H, -pyrr); 9.98 (d, 3J =

4.80 Hz, 2H, -pyrr). HRMS (MALDI-TOF) m/z calcd for

C51H41FeN4: 765.2682; found: 765.2714[M+H]+.

5,10,15,20-tetra(ferrocenyl)porphyrin (10H2).

Argon was bubbled for 15 minutes through a solution of 90

ferrocenecarboxaldehyde (470 mg, 2.2 mmol) and pyrrole (150

L, 2.2 mmol) in 200 mL of anhydrous CH2Cl2. After protecting

the mixture from light, trifluororacetic acid (250 L, 3.3 mmol)

was slowly added. The solution was kept under stirring at room

temperature for 2 h and then neutralized with triethylamine (456 95

L, 3.3 mmol). p-Chloranil (440 mg, 3.3 mmol) was then added

and after stirring the resulting solution at room temperature for 3

h, the solvent was removed under reduced pressure. The crude

compound was purified by column chromatography on silica gel

using CH2Cl2 as the eluent to give 136 mg (24 %) of 10H2. 100

Spectroscopic data found for 10H2 are consistent with those

reported in literature.21

Metallation of the free bases

In a typical experiment, 1 mL of a saturated solution of Zn(OAc)2

in CH3OH was added to a stirred CH2Cl2 solution of the free base 105

(50 mol/20 mL). The mixture was kept under stirring for 10 h at

room temperature and then washed with water. The organic layer

was dried over anhydrous Na2SO4, filtered and then removed

under reduced pressure. The crude product was purified by

column chromatography on silica gel using CH2Cl2 as the eluent 110

to afford the targeted Zn(II) complexes in high yields (> 90 %).

2Zn: 1H NMR (500 MHz, CDCl3, 298 K) (ppm): 2.21 (m, 2H, -

S(CH2)2S-); 2.65 (s, 3H, -Me); 2.67 (m, 8H, -Me and -S(CH2)2S-

); 3.97 (m, 2H, -Fc); 3.99 (m, 2H, -Fc); 4.45 (s, 1H, -HC(S-)2);


4.58 (m, 2H, -Fc); 5.37 (m, 2H, -Fc); 7.52 (m, 6H, -Tol); 8.03 (m,

6H, -Tol); 8.83 (m, 6H, -pyrr); 10.03 (d, 3J = 3,50 Hz, 2H, -

pyrr). UV-vis. (CH2Cl2) λmax, nm (ε, L mol–1 cm–1): 425

(369000); 568 (12600); 619 (13800). HRMS (ESI/TOF) m/z

calcd for C54H42N4FeS2Zn: 930.1488; found: 930.1508 [M]+. 5

3Zn: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): 2.40 – 2.60

(m, 4H, -S(CH2)2S-); 2.70 (s, 6H, -Me); 2.80 – 3.00 (m, 4H, -

S(CH2)2S-); 4.00 (m, 4H, -Fc); 4.11 (m, 4H, -Fc); 4.68 (m, 4H, -

Fc); 4.79 (s, 2H, -HC(S-)2); 5.44 (m, 4H, -Fc); 7.55 (d, 3J = 8.00

Hz, 4H, -Tol); 8.07 (d, 3J = 8.00 Hz, 4H, -Tol); 8.80 (s, 2H, -10

pyrr); 8.85 (d, 3J = 4.50 Hz, 2H, -pyrr); 9.96 (s, 2H, -pyrr);

10.03 (d, 3J = 4.75 Hz, 2H, -pyrr). UV-vis. (CH2Cl2) λmax, nm (ε,

L mol–1 cm–1): 429 (248000); 586 (10200); 640 (19500). HRMS

(ESI/TOF) m/z calcd for C60H48N4Fe2S4Zn: 1128.0751; found:

1128.0775 [M]+. 15

4Zn: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): 2.71 (s, 6H, -

Me); 2.90 - 3.08 (m, 4H, -S(CH2)2S-); 3.09 - 3,24 (m, 4H, -

S(CH2)2S-); 4.12 (m, 4H, -Fc); 4.31 (m, 4H, -Fc); 4.82 (m, 4H, -

Fc); 5.31 (s, 2H, -HC(S-)2); 5.50 (m, 4H, -Fc); 7.56 (d, 3J = 7.50

Hz, 4H, -Tol); 8.07 (d, 3J = 6.75 Hz, 4H, -Tol); 8.81 (d, 3J = 5.00 20

Hz, 4H, -pyrr); 10.01 (d, 3J = 4.00 Hz, 4H, -pyrr). UV-vis.

(CH2Cl2) λmax, nm (ε, L mol–1 cm–1): 428 (261000); 583 (9600);

648 (21000). HRMS (ESI/TOF) m/z calcd for C60H48N4Fe2S4Zn:

1128.0751; found: 1128.0783 [M]+.

5Zn: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): 2.24 - 2,50 25

(m, 6H, -S(CH2)2S-); 2,62 - 2,90 (m, 9H, -Me and -S(CH2)2S-);

3.76 – 4.08 (m, 12H, -Fc); 4.44 – 4.72 (m, 9H, -HC(S-)2 and Fc);

5.30 (m, 6H, -Fc); 7.54 (d, 3J = 7.25 Hz, 2H, -Tol); 8.06 (d, 3J =

7.50 Hz, 2H, -Tol); 8.75 (d, 3J = 5.25 Hz, 2H, -pyrr); 9.79 (d, 3J

= 5.25 Hz, 2H, -pyrr); 9.89 (m, 4H, -pyrr). UV-vis. (CH2Cl2) 30

λmax, nm (ε, L mol–1 cm–1): 432 (207000); 605 (10000);

661(29000). HRMS (ESI/TOF) m/z calcd for C66H54N4Fe3S6Zn:

1326.0015; found: 1326.0044 [M]+.

6Zn: 1H NMR (250 MHz, CDCl3, 298 K) (ppm): 2.66 - 2,82

(m, 8H, -S(CH2)2S-); 2.92 – 3.10 (m, 8H, -S(CH2)2S-); 3.89 (m, 35

8H, -Fc); 4.11 (m, 8H, -Fc); 4.70 (m, 8H, -Fc); 5.00 (s, 4H, -

HC(S-)2); 5.33 (m, 8H, -Fc); 9.79 (s, 8H, -pyrr). UV-vis.

(CH2Cl2) λmax, nm (ε, L mol–1 cm–1): 437 (138000); 627 (8700);

680 (29400). HRMS (ESI/TOF) m/z calcd for C72H61N4Fe4S8Zn:

1524.9357; found: 1524.9380 [M+H]+. 40


Me); 2.72 (s, 6H, -Me); 4.32 (m, 2H, -Fc); 4.44 (m, 2H, -Fc);

4.56 (m, 2H, -Fc); 5.35 (m, 2H, -Fc); 7.44-7,64 (m, 6H, -Tol);

8.00-8.21 (m, 6H, -Tol); 8.63 (s, 1H, -CHO); 8.80-9.03 (m, 6H,

-pyrr); 9.86 (d, 3J = 4.75 Hz, 2H, -pyrr). HRMS (ESI/TOF) m/z 45

calcd for C52H38ON4FeZn: 854.1683; found: 854.1709 [M]+.


Me); 4.54 (m, 4H, -Fc); 4.74 (m, 4H, -Fc); 4.79 (m, 4H, -Fc);

5.57 (m, 4H, -Fc); 7.55 (d, 3J = 7.25 Hz, 4H, -Tol); 8.06 (d, 3J =

7.75 Hz, 4H, -Tol); 8.79 (d, 3J = 5.25 Hz, 4H, -pyrr); 9.01 (s, 50

2H, -CHO); 9,86 (d, 3J = 4.75 Hz, 4H, -pyrr. HRMS (MALDI-

TOF) m/z calcd for C56H40Fe2N4O2Zn: 976,1142; found:

976,1105 [M]+.


Me); 2.71 (s, 6H, -Me); 4.24 (s, 5H, -Fc); 4.82 (m, 2H, -Fc); 5.55 55

(m, 2H, -Fc); 7.48-7.63 (m, 6H, -Tol); 8.00-8.16 (m, 6H, -Tol);

8.81-8.99 (m, 6H, -pyrr); 10.20 (d, 3J = 4.75 Hz, 2H, -pyrr).

HRMS (ESI/TOF) m/z calcd for C51H38N4FeZn: 826.1734; found:

826.1756 [M]+.

Crystallography 60

Crystals of 2Zn, 4Zn, 8Zn and 10Zn were used for data

collection on a SMART CCD diffractometer using Mo-K

graphite-monochromatic radiation (= 0.71073 Å). Intensity data

were corrected for Lorentz, polarization effects and absorption.

Structure solution and refinement were performed with the 65

SHELXTL (v. 5.10; Bruker Analytical X-ray Instruments:

Madison, WI, 1997.package). Data collection and reduction were

conducted with SMART (v. 5.054) and SAINT (v. 6.36A),

respectively, from Bruker Analytical X-ray Instruments.

A summary of the crystallographic data and structure refinement 70

is given in the supplementary material. All non-hydrogen atoms

were refined with anisotropic thermal parameters except for

disordered solvent molecules of THF in 4. Hydrogen atoms were

generated in idealized positions for compound 3 and 4; riding on

the carrier atoms and were found and refined in complex 2, with 75

isotropic thermal parameters for all. Crystal structures have been

deposited at the Cambridge Crystallographic Data Centre and

allocated the deposition numbers CCDC 893172 – 893175. These

data can be obtained free of charge at

www.ccdc.cam.ac.uk/conts/retrieving.html or from the 80

Cambridge Crystallographic Data Centre, 12, Union Road,

Cambridge CB2 1EZ, UK [fax: (inter.) + 44-1223/336-033; e-

mail: [email protected]]

Results and discussion

Synthesis of 2H2-6H2 and their zinc complexes 2Zn-6Zn 85

In previous articles,5,7 we, and the other research groups, have

reported the synthesis of a range of meso-ferrocenyl-porphyrins

from commercially available ferrocenecarboxaldehyde and

pyrrole using a standard Lindsey’s synthetic strategy.22

Purification of the crude products unfortunately proved quite 90

difficult and could only be achieved efficiently on small scales.

These significant drawbacks have hitherto considerably restricted

the application scope of such molecules, like for instance as

intermediates in the synthesis of ferrocene-based “picket-fence”

or “basket handled” porphyrins. Our strategy to overcome these 95

limitations and promote an easy and straightforward post-

functionnalization involves use of dithiolanyl-protected

ferrocene-based starting materials. Synthesis of the targeted

ferrocene-porphyrin conjugates is summarized in Scheme 1. It

starts with the mono-protection of diformyl ferrocene to afford 1 100

in 70% yield19 (Scheme 1). The dithiolanyl group has been

selected i) for its ability to resist to acidic conditions ii) to

enhance the solubility and the polarity of the porphyrin products

and iii) to allow an easy post-functionalization of the ferrocenyl

fragments. The acid-catalyzed Mac Donald-type condensation of 105

1 with one equivalent of 5-tolyldipyrromethane in

dichloromethane, followed by oxidation with p-chloranil, led to a

crude mixture from which 2H2-5H2 (path A, Scheme 1) could be

isolated in 10, 6, 13 and 1% yield, respectively. The tetra-

substituted derivative 6H2 was obtained in 29 % yield using the 110

same procedure starting from pyrrole (path B, Scheme 1).

Metallation of these free-base porphyrins with Zn2+, to yield 2Zn-

6Zn, was then achieved quantitatively using zinc acetate in a

mailto:[email protected]


MeOH–CH2Cl2 solvent mixture.

Scheme 1 Syntheses of the meso-(dithiolanyl)ferrocenyltolylporphyrins 2H2, 3H2, 4H2, 5H2 and 6H2; (i) TFA (1.5 eq.), CH2Cl2, Ar, 298 K, 30 min. ; (ii)

Et3N (1.5 eq.), p-chloranil/THF, 3 h.22

Crystallography 5

Single crystals of 2Zn were grown by slow evaporation of a

deuterated dichloromethane solution (Fig. 1). 2Zn crystallizes in

the C2/c space group of the monoclinic system, with 8

crystallographic independent molecular entities self-assembled in

four distinct columnar structures. The Zn(II) atom is found to lie 10

~0.2 Å above the mean plane formed by the four nitrogen atoms.

The ferrocene unit is slightly twisted with an interplanar angle

between both cyclopentadienyl (Cp) rings of ~5.6°. The zinc ion

is pentacoordinated in a square pyramidal geometry with four

nitrogen atoms in equatorial positions and one sulfur atom, from 15

the dithiolanyl of a neighbouring porphyrin, in apical position

(Zn-S(1)) = 2.658(2) Å (Fig. 2). Iteration of this intermolecular

coordination mode leads to an infinite columnar self-assembled

network wherein each monomer interacts with two neighbours

through Zn-S bonds. The interplanar angle between the 20

covalently linked Cp and the porphyrin plane is of ~51°. In the

coordination polymer, the interplanar angle between the

porphyrin plane and the closest Cp ring, bearing the coordinated

dithiolane, is of 88.6°. This intermolecualr arrangement allows

the observation of rather short HFc-porph distnaces ranging from 25

2.2 to 2.8 Å.


Zn

N(2)N(3)

N(4) N(1)

Fe

S(1)

S(2)

Fig. 1 Ortep23 view of 2Zn, solvent molecules and hydrogen atoms have

been omitted for clarity reasons. Thermal ellipsoids are scaled to a 50%

probability level.

5

Fig. 2 Ortep23 Side view of the crystal packing in 2Zn. Solvent molecules,

hydrogen atoms and tolyl rings have been omitted for clarity reasons.

Thermal ellipsoids are scaled to a 50% probability level.

S(1)

S(2)Fe

Zn

N(2)N(1)

N(2)

N(1)Fe

S(1)

S(2)

Fig. 3 Ortep23 view of 4Zn. Solvent molecules and hydrogen atoms have 10

been omitted for reasons of clarity. Thermal ellipsoids are scaled to a 50%

probability level.

Fig. 4 Partial Ortep23 side view of the crystal packing in 4Zn. Solvent

molecules, hydrogen atoms and tolyl rings have been omitted for clarity 15

reasons. Thermal ellipsoids are scaled to a 50% probability level.

Single crystals of 4Zn have been obtained in THF. The resulting

solid state structure is depicted in Fig. 3. The interplanar angle

between the mean porphyrin plane and the covalently linked Cp 20

ring is of 61.9° and both ferrocenes are found in a slightly more

open conformation (Cp^Cp ~7.58°) than in 2Zn (~5.63°). This

compound is isolated as a single isomer with both ferrocenyl

groups in a syn configuration (,-atropoisomer), both ferrocenes

pointing towards opposite directions. It should be emphasized 25

that prior to this work, every solid-state structures of 5,15-

diferrocenylporphyrins reported in litterature were found in the

presumably more stable ,-conformation.21 The unexpected

,-conformation adopted by 4Zn is thus most probably imposed

by the formation of a self-assembled coordination 30

oligomers/polymers involving the dithiolane substituents and the

zinc(II) cations. The Zn(II) atom lies in the plane defined by the

four nitrogen atoms. The interatomic Fe-Fe distance reaches

13.327(4) Å. The Zn(II) atom is hexacoordinated by four nitrogen

atoms in equatorial positions and by two sulphur atoms from the 35

dithiolane groups of two adjacent molecules ((Zn-S(2)) =

3.160(2) Å and S(2)-Zn-S(2) = 180°, Fig. 4). In the resulting

coordination polymer, each monomer is linked to four neighbours

through Zn-S coordination bonds.

Single crystals of 10Zn have been obtained in THF (Fig. 5). It 40

crystallizes in the C2/c space group of the monoclinic system,


with eight crystallographic independent molecular entities

including the title compound, THF and water. The Zn(II) atom is

found to lie ~ 0.27 Å above the mean plane of the porphyrin

skeleton. It is pentacoordinated by four nitrogen atoms in

equatorial positions and by one oxygen atom from a THF 5

molecule in axial position ((Zn-O(1)) = 2.23(2) Å). As previously

reported for the free base,11,21 the Zn(II) complex is isolated as a

single isomer adopting an ,,, conformation.Add footnote :

“It should be mentioned that previous works carried out on a

trans-dichlorotin(IV)-tetraferrocenylporphyrin suggest that the 10

configuration observed at the solid state might be imposed by

solvent effects (see J. Porphyrins Phthalocyanines, 2011, 15,

612-621)”.

Zn

O(1)

Fe(2)

Fe(4)

Fe(1)Fe(3)

15

Fig. 5 Side Ortep23 view of 10Zn. Thermal ellipsoids are scaled to a 50%

probability level. The carbon atoms of the THF molecule (O(1)) have

been omitted for clarity reasons.

Both ferrocene moieties located on the side of the coordinated

THF molecule are pointing towards opposite directions 20

(backward and frontward on the drawing depicted in Fig. 5), as

opposed to the two other ones pointing in the same direction. The

ferrocenes are tilted of about 41-52° relative to the porphyrin

plane and the Fe-Fe distance ranges from 8.573(3) to 11.732(3)Å

measured between two adjacent (Fe(2)-Fe(3)) or non-25

adjacent (Fe(1)-Fe(3) ferrocenes, respectively.

NMR spectroscopy

NMR spectroscopy allowed us to investigate the steric and

electronic effects of the ferrocene fragments on the porphyrin 30

ring. For the free base compounds (2H2-6H2), the inner NH’s

resonate at high field, below 0 ppm, as the result of the ring

current associated with the aromatic porphyrin (Fig. 6).8

-2-1012345678910

2 6 6 6 2 1 2 2 2 4 9

2 2 2 2 4 4 4 2 4 4 4 8 6

4 4 4 4 4,2 4 4 4 8 6

4 2 2 2 2 9 6 6 6 12 3

8 4 8 8 8 168

a

b,c,d Tol

i

jk

i

i

i

i

-S-(CH2)2-S-

lm

ab

c

d

ba

cd

a,b

a

Tol

-2-1012345678910 / ppm

2

2

2

2

2

NH

NH

NH

NH

NH

2H2

3H2

4H2

5H2

6H2

0 -1 -28 7 6 5 4 3910

Fig. 6 1H NMR spectra of 2H2-6H2 (250 MHz, CDCl3, 295 K). 35

Attribution of each signal is detailed in Scheme 1. The numbers represent

the relative integration values calculated for each signal.

The corresponding broad singlets are observed at –2.31, –1.83, –

1.70, –1.14 and –0.53 ppm on the NMR spectra of 2H2, 3H2,

4H2, 5H2 and 6H2, respectively. As reported by Nemykin et al,21 40

the NH resonance undergoes a downfield shift as the number of

ferrocenyl substituents increases. These changes are clearly

related to a progressive decrease in the porphyrin ring current

which might result from a significant sharing of electron density

between the ferrocene and porphyrin units and/or from the 45

distortion of the porphyrin skeleton following its substitution by

an increasing number of bulky ferrocenyl substituents.9,24 These

steric effects are for instance revealed at the solid state for 10Zn

through the saddle shape of the porphyrin ring (Fig. 5). As

expected, metallation of 2H2-6H2 with zinc(II) was found to 50

enhance the rigidity of the porphyrin skeleton leading to a larger

ring current revealed on the 1H-NMR spectra by the shifts of the

-pyrrolic signals towards lower fields (0.03 < < 0.23 ppm).

The 1H NMR signals attributed to the hydrogen atoms in the

dithiolane ring are conversely observed at higher fields in the 55

metallated species than in the free bases. For instance, the

resonance of the thioacetal proton Hi (see Scheme 1 for

attribution) resonates at 5.51 and 4.45 in the spectrum of 2H2 and

2Zn, respectively. This metal-induced shift is attributed to the

formation of self-assembled coordination oligomers/polymers in 60

solution, wherein the dithiolane protons dive into the shielding

cone of the macrocycle, as observed on the X-ray structures of

2Zn and 4Zn.

The long-range “communication” observed between metallocene

fragments covalently linked through a porphyrin ring has often 65

been attributed to steric effects prohibiting

atropoisomerization.10,11 These dynamic issues have been

adressed in the present study through detailed VT-NMR


investigations conducted with the monoferrocenyl-porphyrin

derivatives 2Zn and 9Zn. For both species, decreasing the

temperature from 300 K to 185 K led to a splitting of the initial

doublet attributed to the -pyrrolic protons Ha and Ha’ (Fig. 7).

At 185 K, rotation does not occur and the ferrocene fragment 5

adopts the tilted conformation observed at the solid state. As a

result, Ha and Ha’ become chemically and magnetically

unequivalent with a chemical shift between both signals reaching

almost 2 ppm. The activation energies corresponding to the

rotational motion of ferrocene in 2Zn† and 9Zn were estimated 10

from coalescence temperatures (Tc)25,26 at 10.4 kcal.mol-1 (Tc =

230 ± 5 K) and 9.2 kcal.mol-1 (Tc= 215 ± 5 K), respectively. Here

again, the higher value found for 2Zn most probably results from

the existence of intermolecular S-Zn coordination bonds occuring

in deuterated chloroform. This assumption is further confirmed 15

by the important upfield shift of the -S-CH2-CH2-S- proton

signals observed upon cooling (from 2.28 ppm at 298 K to -0.24

ppm at 233 K†).

ppm (t1)

302.9 K

292.9 K

288.2 K

283 K

278 K

273 K

263.1 K

258 K

243 K

233 K

223 K

217.7 K

207.8 K

202.9 K

197.6 K

192.7 K

187.6 K

185.3 K

249.1 K

253.1 K

238 K

228 K

213 K

268 K

11.00 10.00 (ppm)

Ha, Ha’

Ha Ha’

9Zn

Fig. 7 Partial 1H NMR spectra of 9Zn in the 185.3 – 302.9 K temperature 20

range (9.10-3 M, CD2Cl2, 500 MHz, 9.2 ≤ ≤ 11.2 ppm).

Ab initio dynamics calculations

These results have been further confirmed by Born-Oppenheimer

dynamics calculations at the DFT level conducted on the most

symetric species 11Zn (Fig. 8). The ab initio dynamics 25

calculations were performed using the CP2K-QuickStep program

at the DFT level with the BLYP functional.28 The basis set was a

double zeta polarized set of gaussian orbitals for the second and

third row atoms and double zeta for the iron and zinc atoms with

the GTH pseudo potentials.29 30

To work around the issue of rare events, the metadynamics30 or

“hills methods” has been used. A series of small repulsive

Gaussian potentials (hills) centred on the current values of the

collective variables were added during the dynamics to prevent

the system from revisiting points in the configurational space of 35

the collective variables. In the present study, we considered the

dihedral angle CFc-CFc-Cporph-Cporph (see Fig. 8) as a collective

variable. A total free energy activation of 10-10.5 kcal.mol-1 was

obtained from the resulting energy profile (Fig. 8). This value is

in very good agreement with the VT NMR experimental data 40

detailed above and it is also found close to values previously

reported for the meso-tetraferrocenyl free base12 and zinc25

porphyrins (10.4 kcal mol-1 and 11.7 kcal mol-1, respectively).

The low activation energy found for the ferrocenyl-substituted

porphyrins 11Zn is thus in agreement with a free rotation of the 45

ferrocenyl subunit at room temperature

Final minimum First minimum

Energy barrier

10.2 Kcal mol1

Fre

e e

nerg

y /

Kca

l m

ol

1

Angle / Degree

250 200 150 100 50 50 100 150

16

14

12

10

8

6

4

2

0

0

11Zn

Fig. 8 Free energy profile corresponding to the rotation motion of one of

the two ferrocenes of 11Zn around the Cmeso-CFc bond.

UV-visible absorption spectroscopy 50

UV-vis. absorption spectrophotometry experiments carried out

with 2-6 also suggest a progressive decrease of the porphyrin-

based aromaticity with the increasing number of covalently

linked ferrocenyl substituents†. As shown in Fig. 9, this effect is

clearly revealed by the increasing bathochromic and hypochromic 55

shifts of the Soret band occuring from 2H2 to 6H2 or from 2Zn

up to 6Zn (Table 1).

Table 1 Maximum absorption wavelengths (max) and molar extinction

coefficients (measured for 2-6 and 2Zn-6Zn in DCM.

2H2 3H2 4H2 5H2 6H2 2Zn 3Zn 4Zn 5Zn 6Zn

max / nm 422 427 425 430 435 425 429 428 432 437

10-3× / M-1 cm-1

331 237 247 187 144 369 248 261 207 138

60


350 400 450 500 550 600 650 700 750 800

0

50

100

150

200

250

300

350 4Zn

5Zn

6Zn

7Zn

8Zn

10-3

x

/ L

.cm

-1.m

ol-1

/ nm

500 550 600 650 700 750 800

0

5

10

15

20

25

302Zn

3Zn

4Zn

5Zn

6Zn

2Zn

3Zn

4Zn

6Zn

5Zn

Fig. 9 UV-vis. absorption spectra of 2Zn-6Zn recorded in DCM at 295 K.

It should also be noted that the larger values found for the trans

isomers (4H2 and 4Zn) than for the cis isomers (3H2 and 3Zn)

suggest a more planar structure for the trans-disubstituted 5

derivatives (see Table 1). For all the investigated species,

metallation with Zn2+ resulted in the bathochromic shifts of the

main absorption bands along with a significant increase of the

associated molar extinction coefficients.

Electrochemistry 10

The electrochemical behavior of 2H2-6H2 and of their Zn2+

complexes has been investigated by cyclic voltammetry (CV) and

by voltammetry at rotating disk electrodes (RDE) in

dichloromethane (DCM) or in N,N-dimethylformamide (DMF)

solutions. All potentials have been referenced towards the half-15

wave potential of decamethyl-ferrocene (DMFc/DMFc+) used as

an internal reference. Electrochemical data determined from CV

experiments are collected in Table 2. The electrochemical

signature of all the investigated compounds arises from electron

transfers centred on the ferrocene (Fc) and on the porphyrin (P) 20

moieties. In DCM, the oxidation of the dithiolane substituents is

also observed as two irreversible waves at Epa = 1.20 and 1.46

V†. As a general statement, the signature of the ferrocene and

porphyrin units are strongly affected by the extended

conjugation within the molecules.9-11,24 The ferrocene groups are 25

reversibly oxidized at potential values ranging form +500 to +750

mV (Fig. 10). The electron withdrawing effect of the porphyrin

ring on the ferrocene centre is revealed on the CV of 2H2 through

the anodic shift of the ferrocene-centred one-electron oxidation

wave (E1/2 = + 0.64 V) as compared to that of ferrocene used as a 30

reference (E1/2 = +0.54 V). For the trans disubstituted ferrocenyl

compound 4H2, the CV curve displays two distinct waves

whereas a single signal flanked by two shoulders is seen on the

CV curve of the cis isomer 3H2. According to RDE voltammetry

experiments, the overall number of exchanged electron is in 35

agreement with the number of ferrocene units, ie two

electrons/molecule.

The electrochemical signatures of the tri- and tetra-substituted

ferrocenyl compounds feature two consecutive waves observed

with 1/2 and 1/3 intensity ratios, respectively. The shape of these 40

signals indicates that the chemically equivalent Fc subunits in the

di-, tri- and tetra-substituted porphyrins are electrochemically non

equivalent, the oxidation of one Fc centre shifting the oxidation

of the remaining ones towards higher potential values.

5A

0.1V

2H2

Epa = 0.690 V

Epc = 0.595 V

5 A

0.1 V

3H2

Epc = 0.580 V

Epa = 0.730 V

5A

0.1V

4H2

Epc = 580 V

Epa = 0.790 V

5 µA

0.1 V

6H2

Epc = 0.520V

Epa = 0.800 V

5 A

0.1 V

5H2

Epc = 0.565 V

Epa = 0.790 V

45

Fig. 10 Cyclic voltammograms of 2H2-6H2 limited to the potential range

corresponding to the oxidation of the ferrocene units (5.10-4 M, 100 mV s-

1, DCM 0.1 M TBAP, glassy carbon working electrode Ø = 3 mm,

reference: DMFc/DMFc+).

Simulation and best fitting of the experimental data were used to 50

determine the formal potentials of each ferrocenyl subunits in

3H2, 4H2 and 5H2†. These data are collected in Table 2.

Unfortunately, adsorption of the oxidized complex 6H2n+ onto the

electrode surface, as revealed by the observation of a desorption

peak on the reverse scan of the CV curve, precluded the 55

determination of the corresponding formal potentials. Theoretical

developments carried out with molecules submitted to n

successive one-electron transfers centred on fully independent

and chemically equivalent redox sites have established that the

shift between each successive formal potentials should equal 60

35.6, 28.5 and 23.7 mV when n = 2, 3 and 4, respectively, the

resulting CV curve however still displaying the same peak to

peak separation of 60 mV.14 The latter feature is not observed on

the ferrocene centred oxidation signals depicted in Fig. 10

showing multiple shoulders and splitting attributed to the 65

interactions occuring between each redox site in the oxidized

and/or reduced states.10,17,24

The extent of the “communication” between ferrocene centres

furthermore evolves with the relative position of each

metallocenes on the porphyrin skeleton. The differences in the 70

shape of the CV waves recorded with the bisferrocenyl isomers

3H2 and 4H2 for instance suggest that the coupling is stronger in

the trans isomer 4H2 than in the cis isomer 3H2. These findings

contrast with previous works, carried out by Swarts13 or

Nemikyn21 on similar molecules. Swarts and coworkers found no 75

significant differences between the first and second ferrocene-

centered oxydations of cis and trans porphyrin isomers (111 and

115 mV for “2HPtrans” and “2HPcis”, respectively and 102 and

103 mV for “ZnPtrans” and “ZnPcis”, respectively), whereas

Nemykin reported a much higher E value for a cis isomer (208 80

mV) than for a trans isomer(150 mV).”In our experimental

conditions, the potential shifts between both ferrocene oxidation

processes in 3H2 and 4H2 were found to reach 85 mV and 115

mV, respectively. These data confirm the fact that the electronic

“coupling” between both ferrocenyl substituents is stronger in 85

4H2, although the Fe···Fe distance happens to be much higher in

the trans isomer (11.5 < d < 13.5 Å) than for in the cis one 3 (6.2

< d < 11.1 Å). The extent of the bended or ruffled deformations

of the porphyrin skeleton induced by the presence of two bulky

ferrocenyl substituents in the 5,10 or 5,15-positions of the 90

macrocycle is another key factor which will undoubtly affect the

mixing of molecular orbitals involved in the through-bond


“communication” between ferrocene centres. Unfortunately,

failure to obtain X-ray data for the cis isomer did not allow to

draw clear cut conclusions on these structural aspects. In that

regard, it should be mentionned that 1H NMR data do not support

the assumption of a weaker ring current in 3H2 than in 4H2. 5

CV curves of porphyrins (P) usually display two successive one-

electron oxidation waves involving formation of P•+ and P2+, as

well as two successive one-electron reduction waves leading to

the formation of the radical anion (P•-) and di-anion (P2-).31 In all

studied compounds, the potential separations between the first 10

porphyrin oxidation and first porphyrin reduction potentials are in

accordance with the standard HOMO-LUMO gap of ca. 2.2 V

commonly measured with porphyrins.32

The electrodonating effect of the ferrocenyl group(s) on the

porphyrin ring is enlightened by comparison between the 15

reduction potentials of 2H2-6H2 or 2Zn-6Zn and those of the

reference compounds TPPH2 and TPPZn. The first reductions of

2Zn and TPPZn are For instance observed at -1.305 V and -

1.205 V, respectively. In addition, the nature of the solvent used

for analyses has been shown to affect quite significantly the 20

number and the reversibility of the observed redox processes.

Table 2 Electrochemical data for 2H2, 3H2, 4H2, 5H2, 6H2 and their Zn complexes (5.10-4 M in DMF or CH2Cl2 0.25 M TBAP, = 0.1 V s-1, E vs.

DMFc/DMFc+).

Solvent

E1/2 2H2 3H2 4H2 5H2 6H2 7H2 8H2 2Zn 3Zn 4Zn 5Zn 6Zn

6Zn 6Zn

DMF (P-•/P2-) –1.530 –1.505 –1.510a –1.495 –1.530 –

1.720 –1.675

–1.700a

–1.690a

–1.680a

DMF (P/P-•) –1.090 –1.100 –1.080 –1.110 –1.120 –

1.350 –1.345

–

1.325

–

1.340

–

1.335

DMF (Fc/Fc+) 0.590 b b b b 0.535 b b b b

DMF (P/P+•) 1.080 1.210 b b 1.020 0.855 0.910 0.920 1.000 b

DCM (P-•/P2-) –1.520 –1.590a –

1.745a

–

1.740a

DCM (P/P-•) –1.125 –1.160 –

1.305

–

1.310

DCM (Fc/Fc+) 0.640 0.615c

0.700c

0.605c

0.720c

0.585c 0.695c

0.725c

b

0.600 0.555c

0.645c

0.545c

0.655c

0.510c 0.665c

0.685c

b

DCM (P/P+•) 1.135d 1.210d 1.180d 1.135d 1.070d

0.895 ~1.070 0.975 ~1.11 ~1.08

5

aEpc, irreversible; bExtensive overlaps occurring between successive redox systems (ferrocene, porphyrin or electrolyte-centered) prohibits an accurate

experimental determination of this E1/2 value; cfrom best fitting; dEpa, irreversible.25

Two successive one-electron reduction waves are systematically

observed in DMF medium, whereas formation of the di-cation P2+

species are only observed in CH2Cl2. The potential values as well

as the reversibility of the porphyrin-centred electron transfers also

turn out to undergo significant variations with the substitution 30

pattern and with the insertion of Zn2+. As observed with most

porphyrins,10,31 the redox processes of the free bases are shifted

towards more negative potentials (ca. −200 mV) upon metallation

with Zn2+. In dichloromethane, the irreversibility of the first

oxidation of the free base porphyrins suggests the existence of a 35

follow-up chemical reaction. On the contrary, the first oxidation

of the zinc porphyrins appears reversible at the cyclic

voltammetry time scale.

Spectroelectrochemistry

Absorption spectra were recorded periodically throughout bulk 40

electrolyses experiments carried out in CH2Cl2. In all cases,

oxidation of the ferrocene units leads to a decrease in the

intensity of the Soret band along with a slight hypsochromic shift

of its maximum wavelength. These changes are in agreement

with the electron withdrawing character of the electrogenerated 45

ferrocenium and with the delocalization of the positive charge

over the whole aromatic macrocycle.11,17

The exhaustive oxidation of the ferrocene unit in 2H2 (Eapp = 0.81

V) was for instance accompanied with a progressive color change

from brown/green to pale green. After the uptake of one electron, 50

the initial Soret band at 422 nm ( = 331x103 M-1 cm-1) had lost

2/3 of its initial intensity ( = 118300 M-1 cm-1) at the expense of

a new band developping at 448 nm ( = 76200 M-1 cm-1). The

reversibility of these transformations was checked through a bulk

back reduction (Eapp = 0.51 V) of the resulting ferricinium 55

appended porphyrin allowing to restore the initial spectrum.

Further oxidation carried out at 1.26 V and uptake of another one

electron/molecule (1 < Qtotal < 2.1 electron/molecule, Fig. 11),

led to the development of the signal at 448 nm ( = 2 x105 M-1

cm-1) and to the disappearance of the initial Soret band at 422 nm. 60

The irreversiblity of the oxidation was revealed by the fact that

the signature of the starting material could not be restored by

back reduction of the doubly oxidized species. This irreversibility

was further confirmed by CV analysis of the electrolyzed solution

(obtained after uptake of two electrons from 2H2 at Eapp = 1.26 V) 65

showing a reversible oxidation wave at 0.81 V and a reversible

reduction at –0.36 V. This signature was not only found different

from that of the starting material, as expected for a species

produced irreversibly from the electrogenerated dicationic species

2H22+, it was most importantly found to hold great similarities 70

with that of the doubly-protonated H4TPP2+ species.33 To confirm

our hypothesis that protonation of the porphyrin ring might be

involved, we carried out a detailled characterization of 2H42+

produced in CH2Cl2 from 2H2 upon addition of increasing

amounts of trifluoroacetic acid (TFA). Addition of up to 2 molar 75

equivalents of TFA led to the progressive disappearance of the

Soret band at 422 nm along with the development of a new band

at 448 nm attributed to 2H42+. Additionaly, the CV curve of the


diprotonated species 2H42+ and that of the species produced by

bulk oxidation of 2H2 turned out to display similar key features

including the reversible waves at 0.80 V and −0.36 V. These

results led us to conclude that the electrogenerated dication 2H22+

is not stable in anhydrous CH2Cl2 and readily evolves towards 5

2H42+. It should be mentioned that similar proton exchanges

involving oxidized tetrapyrrolic macrocycles or nitrogen

containing aromatic compounds34,35 have been explained as

resulting from the presence of oxidizable and protic substrate in

the electrolyte (solvent, traces of water …). 10

The proposed course of events was further confirmed with

spectroelectrochemical investigations carried out with the

metallated species 2Zn. The first, ferrocene-centred, electron

transfer remains reversible at the time scale of electrolysis but the

UV-vis. signature of the electrogenerated species 2Zn+• is 15

completely different from that observed with 2H2. As seen on the

spectra shown in Fig. 12, the intensity of the Soret band decreases

down to = 151000 M-1 cm-1 while a new broad band appears at

822 nm. The magnitude of the modifications in the porphyrin-

based signature, proceeding through well defined isosbetic points 20

at 415, 558, 577, 601 and 622 nm, have been attributed to

delocalization of the electron hole (radical cation character) over

the whole molecule from the ferrocene centre to the porphyrin

ring.

300 400 500 600 700 800 900

0.0

0.5

1.0

1.5

2.0

2.5

680

448

Abs./

a.u

.

/ nm

422

500 600 700 800 900

0.00

0.05

0.10

0.15

0.20

0.25

Abs.

/ a.u

.

/ nm

680

25

Fig. 11 Electrolysis of a 10-4 M solution of 2H2 followed by UV-Vis.

spectroscopy (l = 1 mm, 0.25 M TBAP in CH2Cl2, Eapp = 1.26 V, -2.1 e).

Oxidation of 2Zn+• carried out at 1.07 V, corresponding to the

first porphyrin-centred electron transfer, is accompanied by a

further decrease in the intensity of the Soret and Q bands. These 30

changes turned out to be however fully irreversible at the

electrolysis time scale since the signature of the starting solution

could not be restored by back reduction. In summary, these

results not only demonstrate that the doubly oxidized species

2Zn2+ is poorly stable at the electrolysis time scale, it also 35

supports our assumption that the bulk oxydation of 2H2 yields

quantitatively 2H42+

The UV-Vis absorption spectra recorded periodically as 4H2 was

subjected to electrochemical oxidations were found to be similar

to those monitored with 2H2. The successive oxidations carried 40

out at 0.71 V (1 electron/molecule) and then at 0.86 V (1

additionnal electron/molecule) were accompanied by the

progressive decrease in the intensity of the initial Soret band at

426 nm at the expense of a new band developping at 453 nm ( =

132500 M-1cm-1†). The overall process was found to be fully 45

irreversible at the time scale of electrolysis and a CV analysis of

the resulting oxidized solution revealed two reversible oxidation

waves at 0.78 V and 0.90 V attributed to the oxidation of the Fc

centres and one reduction process at -0.37 V attributed to the

protonated porphyrin ring electrochemical response. As seen with 50

the mono-ferrocenyl derivative, the electrochemical and

spectrophotometric signatures of the electrolyzed solution match

those of the diprotonated species 4H42+ which could be produced

in situ by addition of TFA to a solution of the free base 4H2†.

300 400 500 600 700 800 900

0.0

0.5

1.0

1.5

2.0

2.5

500 600 700 800 900

0.02

0.04

0.06

0.08

0.10

0.12

Ab

s.

/ a

.u.

/ nm

822

Abs.

/ a.u

./ nm

425

55

Fig. 12 Electrolysis of a 10-4 M solution of 2Zn followed by UV-Vis.

spectroscopy (l = 1 mm, 0.25 M TBAP in CH2Cl2, Eapp = 1.07 V, -2.1 e).

The oxidized forms of this bisferrocenylporphyrin derivative

were found to be greatly stabilized by insertion of a zinc atom

within the porphyrin ring and the reversibility of both ferrocene-60

centred oxidation processes was cheked from back-reduction

experiments allowing to recover the UV-Vis absorption spectrum

of the starting material 4Zn. The electrochemical oxidation of

4Zn into 4Zn2+ was revealed by the hypochromic shift of the

Soret band from = 261000 M-1 cm-1 down to = 126000 M-1 65

cm-1 and by the growth of a new band at 850 nm (= 9700 M-

1.cm-1). As discussed for the monoferrocenyl-porphyrin analog

2Zn, the magnitude of these changes, involving porphyrin-based

-* transitions, support the assumption of an extended

delocalization of the electrogenerated positive charges over the 70

entire molecule, i.e. from the ferrocene centres to the porphyrin

macrocycle.

Removal of the 1,3-dithiolanyl protecting group

The 1,3-dithiolanyl protecting groups have been introduced on

the upper ring of the ferrocene fragments to allow a 75

straightforward post-functionnalizations and an easy access to a

range of redox active picket-fence porphyrins. Numerous

chemical or electrochemical strategies have been considered to

remove the dithiolane protecting groups in 2H2 and 4H2 and we

found that the most efficient and mildest procedure for 80

synthesizing the targeted formylated compounds 7H2 and 8H2 in

good yields (Scheme 2) involves Ag+ in the presence of N-

chlorosuccinimide.5 The 1H-NMR spectra of 2H2 and 7H2

indicates that the inner NH resonances are shifted upfield upon

hydrolysis of the dithiolane substituents (-2.31 and -2.36 ppm, 85

respectively). This shift is also observed for 4H2 and 8H2 (-1.70

and -1.76 ppm, respectively). Removal of the dithiolane group is

further confirmed by the disappearance of the multiplets near

3.05-3.40 ppm for 2H2 and 4H2 along with the appearance of the


characteristic singlet of the aldehyde function(s) at 9.89 and 9.90

ppm for 8H2 and 7H2, respectively. The corresponding Zn2+

complexes 7Zn and 8Zn could be obtained using Zn(OAc)2 as a

metal source following classical metalation procedures.

Single crystals of 8Zn were obtained by slow diffusion of 5

methanol into a solution of 8Zn in CHCl3. It is formulated as

C58H48N4Fe2O4Zn and crystallizes in the P-1 space group of the

triclinic system, revealing one crystallographic independent

molecular entity consisting of one 8Zn entity and two methanol

molecules. 8Zn is isolated as a single isomer with both ferrocenyl 10

groups adopting a syn conformation (,-atropoisomer), this

latter being favored due to hydrogen bonds between the two

coordinated MeOH molecules and the aldehyde functions (Fig.

13). The interplanar angle between the covalently linked Cp and

porphyrin planes is of ~34.7° whereas the ferrocene is slightly 15

twisted with an interplanar angle between both Cp rings of ~6.3°.

The Zn(II) atom lies inside the porphyrin plane and is coordinated

by four nitrogen atoms of the macrocycle, with bond distances

ranging from 2.043(2) to 2.059(2) Å and by two oxygen atoms

from two methanol molecules bound in axial positions (Zn-O(2)) 20

= 2.494(2) Å). The Fe-Fe distance is 12.775(2) Å and both

hydroxyl groups are H-bonded to the oxygen atoms of the

aldehyde units (O(1)···H-O(2) = 2.882(4) Å).

Scheme 2 (i) NCS (6 eq.), AgNO3 (6 eq.) in THF/CH3CN/H2O, 70%; (ii) 25

NCS (12 eq.), AgNO3 (12 eq.) in THF/CH3CN/H2O, 50%.35

Zn

N(2)

N(1)

N(2)

N(1)

Fe

FeO(2)

O(1)

Fig. 13 Ortep23 views of 8Zn. Thermal ellipsoids are scaled to a 50%

probability level.

Further evidences of the high electronic coupling between the 30

ferrocene and porphyrin units came from electrochemical

investigations carried out with the protected and deprotected

derivatives 4H2 and 8H2, respectively. While the conversion of

the dithiolane rings into formyl groups proved to have no

significant effect on the shape of the observed CV waves, it led to 35

large shifts of the associated half-wave oxidation and reduction

potential towards more positive values. These results thus reveal

that (i) the magnitude of the electronic coupling between both

iron centres is similar in both species, and that (ii) the electron-

withdrawing character of the formyl groups is efficiently 40

transmitted to the ferrocene sub unit and to a lesser extent to the

porphyrin, their electrochemical signatures being shifted

positively of + 200 mV and + 70 mV, respectively.

Potential / V vs. DMFc/DMFc+

0.35-0.05 0.75-0.45-0.85-1.25

5 µA

Fig. 14 Cyclic voltammograms of 4H2 (dotted line) and 8H2 (solid line) 45

(5.10-4 M, 100 mV s-1, CH2Cl2 0.1 M TBAP, WE: glassy carbon Ø = 3

mm, CE: Pt wire, Ref: DMFc/DMFc+).

Conclusions

A -conjugated porphyrin ring has been used as an electron-

conducting linker enabling effective electronic interactions 50

between two, three or four ferrocene centers. Dithiolanyl-

protected ferrocenes have been introduced at the meso positions

of the porphyrin ring using a classical Lindsey-like synthetic

strategy involving use of pyrrole or dippyrromethane as starting

materials. Dithiolanyl substituants have been selected to allow a 55

straightforward post-functionnalization of the targeted redox-

responsive picket-fence porphyrins. Atropoisomerization issues

have been adressed by VT NMR and by metadynamic

calculations. The low activation energy of around 10 Kcal/mol

found for the bisferrocenylporphyrin 11Zn is in agreement with 60

a free rotation at room temperature of the ferrocenyl subunit

around the CFc-CPorph bond.

X-ray diffraction analyses of the mono- and bis-ferrocenyl


porphyrin derivatives 2Zn and 4Zn revealed the existence of S-

Zn bonds involved in supramolecular arrays. The solid state

structure of the zinc complex 8Zn obtained after removing the

dithiolanyl protecting group, is conversely found as a monomer

exibiting an unusual hexacoordinated zinc metal centre. 5

The electronic connection between ferrocene and porphyrin and

between ferrocene centers has been investigated by spectrocopic

and electrochemical methods. Interestingly, the interaction

appears stronger for the trans di-substituted ferrocenyl

macrocycle than for the cis isomer. The effective electronic 10

“communication” through the whole molecule was further

confirmed by bulk electrolyses experiments. Oxydation of the

ferrocene centers in 2H2 or in 4H2 was found to produce the

protonated species 2H42+ or 4H4

2+, respectively. The exact

succession of electrochemical and chemical steps leading to these 15

species is still unknown but their formation support the notion

that the electrogenerated positive charge is significantly

delocalized over the macrocycle. It is noteworthy to mention that

deprotection of the dithiolanyl-substituted ferrocenes could be

readily achieved without loss of the ferrocene and porphyrin-20

based electrochemical activity.

Future works will be devoted to the synthesis of functionnalized

ferrocene-based picket fence porphyrins which could find

applications in supramolecular chemistry, in electrochemical

recognition or in molecular electronics. 25

Aknowledgement

The authors would like to thank the “centre national de la

recherche scientifique”, the “université Joseph Fourier”, the

“conseil régional de Bourgogne” and the “université de

Bourgogne” for their financial support. C. H. D. would like to 30

thank Dr. Fanny Chaux for carrying out the ESI-MS analyses. A.

M. whishes to thank the “région Rhône-Alpes” as well as the

CECIC calculation facility.

Notes and references

a Institut de Chimie Moléculaire de l’Université de Bourgogne, UMR 35

CNRS 6302, Université de Bourgogne, BP 47870, 21078 Dijon Cedex,

France. b Département de Chimie Moléculaire, UMR CNRS 5630, Université

Joseph Fourier, BP 53, 38041, Grenoble Cedex 9, France. E-mail:

[email protected]; Fax: (33)476514267; Tel: (33)47651 40

4682. c CEA/DRMFC/SCIB, Laboratoire de coordination et nanochimie, 17 rue

des Martyrs, 38054, Grenoble Cedex 9, France.

† Electronic Supplementary Information (ESI) available: Experimental

details and characterization data. See DOI: 10.1039/b000000x/ 45

1. C. Bucher, C. H. Devillers, J.-C. Moutet, G. Royal and E. Saint-

Aman, Coord. Chem. Rev., 2009, 253, 21.

2. D. T. Gryko, F. Zhao, A. A. Yasseri, K. M. Roth, D. F. Bocian, W.

G. Kuhr and J. S. Lindsey, J. Org. Chem., 2000, 65, 7356; Q. Li, G. 50

Mathur, S. Godwa, S. Surthi, Q. Zhao, L. Yu, J. S. Lindsey, D. F.

Bocian and V. Mistra, Adv. Mater., 2004, 16, 133; L. Wei, K.

Padmaja, W. J. Youngblood, A. B. Lysenko, J. S. Lindsey and D. F.

Bocian, J. Org. Chem., 2004, 69, 1461.

3. Z. Liu, A. A. Yasseri, J. S. Lindsey and D. F. Bocian, Science, 2003, 55

302, 1543.

4. K. Matsushige, H. Yamada, H. Tada, T. Horiuchi and X. Q. Chen,

Ann. N. Y. Acad. Sci., 1998, 852, 290.


Aman, Chem. Commun., 2003, 888. 60


Aman, New J. Chem., 2004, 28, 1584.

7. D. N. Hendrickson and R. G. Wollmann, Inorg. Chem., 1977, 16,

3079; N. M. Loim, N. V. Abramova and V. I. Sokolov, Mendeleev

Communication, 1996, 46; N. M. Loim, N. V. Abramova, R. Z. 65

Khaliullin and V. I. Sokolov, Russ. Chem. Bull., 1997, 46, 1193; V.

A. Nadtochenko, N. N. Denisov, V. Y. Gak, N. V. Abramova and N.

M. Loim, Russ. Chem. Bull., 1999, 48, 1900; S. J. Narayanan, S.

Venkatraman, S. R. Dey, B. Sridevi, V. R. G. Anand and T. K.

Chandrashekar, Synlett, 2000, 12, 1834; V. A. Nadtochenko, D. V. 70

Khudyakov, E. V. Vorontsov, N. M. Loim, F. E. Gostev, D. G.

Tovbin, A. A. Titov and O. M. Sarkisov, Russ. Chem. Bull., 2002, 51,

986; B. Koszarna, H. Butenschön and D. T. Gryko, Org. Biomol.

Chem., 2005, 3, 2640; O. Shoji, S. Okada, A. Satake and Y. Kobuke,

J. Am. Chem. Soc., 2005, 127, 2201; O. Shoji, H. Tanaka, T. Kawai 75

and Y. Kobuke, J. Am. Chem. Soc., 2005, 127, 8598; A. Auger, A. J.

Muller and J. C. Swarts, Dalton Trans., 2007, 3623; S.

Ramakrishnan, K. S. Anju, Ajesh P. Thomas, E. Suresh, A.

Srinivasan, Chem. Comm. 2010, 46, 4746; S. Ramakrishnan, K. S.

Anju, Ajesh P. Thomas, K. C. Gowri Sreedevi; P. S. Salini, M. G. 80

Derry Holaday, Eringathodi Suresh, A. Srinivasan,

Organometallics 2012, 31 (11), 4166; Bucher, C.; Devillers, C. H.;

Moutet, J.-C.; Pécaut, J.; Royal, G.; Saint-Aman, E.; Thomas, F. J.

Chem. Soc., Dalton Trans. 2005, 3620.

85

8. N. M. Loim, N. V. Abramova, R. Z. Khaliullin, Y. S. Lukashov, E.

V. Vorontsov and V. I. Sokolov, Russ. Chem. Bull., 1998, 47, 1016.

9. S. W. Rhee, B. B. Park, Y. Do and J. Kim, Polyhedron, 2000, 19,

1961.

10. H. J. Kim, Rhee S. W., Na Y. H., Lee K. P., Do Y. Jeoung S. C., 90

Bull. Korean Chem. Soc, 2001, 22, 1316.

11. S. Venkatraman, Prabhuraja V., Mishra R., Kumar R., Chandrashekar

T. K., Teng W. and Senge K.R., Indian J. Chem., 2003, 42A, 2191.

12. V. N. Nemykin, C. D. Barrett, R. G. Hadt, R. I. Subbotin, A. Y.

Maximov, E. V. Polshin and A. Y. Koposov, Dalton Trans., 2007, 95

3378.

13. A. Auger and J. C. Swarts, Organometallics, 2007, 26, 102.

14. F. Ammar and J. M. Saveant, J. Electroanal. Chem., 1973, 47 115; J.

B. Flanagan, S. Margel, A. J. Bard and F. C. Anson, J. Am. Chem.

Soc., 1978 100, 4248. 100

15. K.-W. Poon, W. Liu, P.-K. Chan, Q. Yang, T.-W. D. Chan, T. C. W.

Mak and D. K. P. Ng, J. Org. Chem., 2001, 66, 1553; L. M. Tolbert,

X. Zhao, Y. Ding and L. A. Bottomley, J. Am. Chem. Soc., 1995,

117, 12891; A.-C. Ribou, J.-P. Launay, C. Joachim and A. Gourdon,

Inorg. Chem., 1996, 35. 105

16. C. Patoux, C. Coudret, J.-P. Launay, C. Joachim and A. Gourdon,

Inorg. Chem., 1997, 36, 5037.

17. K. M. Kadish, Xu Q. Y., Barbe J.-M., Inorg. Chem., 1987, 2566.

18. G. G. A. Balavoine, G. Doisneau and T. Fillebeen-Khan, J.

Organomet. Chem., 1991, 412, 381. 110

19. B. Basu, S. K. Chattopadhyay, A. Ritzen and T. Frejd, Tetrahedron

Asymmetry, 1997, 8, 1841.


20. J.-W. Ka and C.-H. Lee, Tetrahedron Lett., 2000, 41, 4609.

21. V. N. Nemykin, G. T. Rohde, C. D. Barrett, R. G. Hadt, J. R. Sabin,

G. Reina, P. Galloni and B. Floris, Inorg. Chem., 2010, 49, 7497.

22. J. S. Lindsey, H. C. Hsu and I. C. Schreiman, Tetrahedron Lett.,

1986, 27, 4969. 5

23. L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.

24. P. D. W. Boyd, A. K. Burrell, W. M. Campbell, P. A. Cocks, K. C.

Gordon, G. B. Jameson, D. L. Officer and Z. Zhao, Chem. Commun.,

1999, 637.

25. V. N. Nemykin, M. McGinn, A. Y. Koposov, I. N. Tretyakova, E. V. 10

Polshin, N. M. Loim and N. V. Abramova, Ukr. Khim. Zh., 2005, 71,

79.

26. H. Günther, La spectroscopie de RMN, MASSON edn., MASSON,

1993.

27. cp2k, <http://cp2k.berlios.de> (2000-2005); J. V. d. Vondele, M. 15

Krack, F. Mohamed, M. Parrinello, T. Chassaing and J. Hutter,

Comp. Phys. Com., 2005, 167, 103.

28. A. D. Becke, Phys. Rev. A, 1998, 38, 3098; C. T. Lee, W. T. Yang

and R. G. Parr, Phys. Rev. B, 1988, 37, 785.

29. S. Goedecker, M. Teter and J. Hutter, Phys. Rev. B, 1996, 54, 1703; 20

C. Michel, A. Laio, F. Mohamed, M. Krack, M. Parrinello and A.

Milet, Organometallics, 2007, 26, 1241.

30. A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. USA, 2002, 99,

12562.

31. K. M. Kadish, Caemelbecke E. V. and Royal G., in Porphyrin 25

handbook, Academic Press, New York, 1999, vol. VIII.

32. P. D. Beer and S. S. Kurek, J. Organomet. Chem., 1987, 336, C17; K.

M. Kadish, Prog. Inorg. Chem., 1986, 34, 435.

33. C. Inisan, J.-Y. Saillard, R. Guilard, A. Tabard and Y. L. Mest, New

J. Chem., 1998, 823. 30

34. K. L. Handoo, J.-P. Cheng and V. D. Parker, Acta Chem. Scand.,

1993, 47, 626; J.-P. Gisselbrecht, M. Gross, E. Vogel and S. Will, J.

Electroanal. Chem., 2001, 505, 170.

35. E. J. Corey and B. W. Erickson, J. Org. Chem., 1971, 36, 3553.

35

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Long-range electronic connection in picket-fence like ferrocene–porphyrin derivatives

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