A one-pot synthesis of disiloxy, dihalo and dithiocyanato dioxo complexes bearing a bidentate...

A one-pot synthesis of disiloxy, dihalo and dithiocyanato dioxocomplexes bearing a bidentate N-ligand from sodiumor potassium molybdate tungstate and perrhenate

Henri Arzoumanian Æ Robert Bakhtchadjian ÆGiuseppe Agrifoglio Æ Reinaldo Atencio ÆAlexander Briceno

Received: 14 May 2008 / Accepted: 17 June 2008 / Published online: 20 September 2008

� Springer Science+Business Media B.V. 2008

Abstract Disiloxy, dichloro, dibromo and dithiocyanato

molybdenum, tungsten and rhenium-oxo complexes bear-

ing bidendate N-ligands have been synthesized in a one-pot

process and fully characterized spectroscopically. The

reaction, in acetonitrile, is significantly simpler to run than

previously reported methods for the synthesis of analogous

compounds and appears to be general in character.

Introduction

Transition metal-oxo species have aroused great interest in

recent years due to their presence either as precursors or as

real active species in many catalytic reactions. Function-

alizing metal-oxo compounds in order to achieve judicious

modifications of the coordination sphere of the metal has,

thus, received considerable attention. One method exten-

sively used has been the reaction with chlorosilanes,

resulting either as chlorination or siloxylation. As a general

rule, chlorination is obtained when trimethylchlorosilane is

used, whereas the siloxy compound is formed when a

bulkier trialkyl or triphenylchlorosilane is used.

LMO3 þ 2Me3SiCl! LMO2Cl2 þMe3SiOSiMe3

½MOn��2 þ 2Ph3SiCl! MOn�2ðOSiPh3Þ2 þ 2Cl�

As an illustration, trimethylchlorosilane leads readily

to mono or dichloro compounds with many metal-oxo

complexes bearing various ligands such as: Me3ReO3 [1],

(g5-C5Me5)2WO [2], (g5-C5Me5) MoO3 [3], (g5-C5Me5)ReO3

[1], bis(diethyldithiocarbamate)MoO2 [4], bis(dithiolene)

WO2 [5], bis(N-pyrrolidinedithiocarbamate)MoO2 [6]. A

few exceptions do exist, however, to this general trend such

as for AgReO4 and AgTcO4 [3]. When a methyl group in

Me3SiCl is replaced by a bulkier group such as tert-butyl or

when triphenylchlorosilane is used, the reaction with a metal-

oxo yields stable siloxy compounds. For example, Ag2MoO4

[7], (g5-C5Me5) WO3 [7] bis(diethyldithiocarbamate)MoO2

[4, 8], AgVO3 [7], Ag2MoO4 [8], bis(dithiolene)2WO [5].

In most cases, however, obtaining a metal-oxo species

bearing a chloro or a siloxy group as well as a ligand

necessitates at least two separate steps, either the metal-oxo

bearing a ligand is synthesized and then treated with the

chlorosilane [1–6] or the chloro or siloxy compound sepa-

rately prepared is then complexed with the desired ligand [8].

More recently, a more direct and simpler procedure was

reported for the silylation of potassium tungstate in the

presence of a bidentate ligand [9]. The use of acetonitrile as

a solvent was apparently the necessary medium for such an

improvement. We have now extended this reaction mode to

potassium and sodium molybdate and also showed that it

can be applied to the chlorination, bromination and thio-

cyanation of molybdate and tungstate ions in the presence

of various ligands as depicted below.

½MoO4��2 þ Lþ 2Ph3SiCl! LMoO2ðOSiPh3Þ2 þ 2Cl�

½MO4��2 þ Lþ 4Me3SiX! LMO2X2 þ 2Me3SiOSiMe3

þ 2X�

M=Mo, W; X=Cl, Br, NCS; L = 4,40-substituted-2,20-bipyridine, bis(3,5-dimethylpyrazol-1-yl)methane.

It was further tested with potassium perrhenate.

H. Arzoumanian (&) � R. Bakhtchadjian

Chirosciences UMR 6263 CNRS ISM2, Universite Paul

Cezanne, Faculte des Sciences, St. Jerome, Marseille, France

e-mail: [email protected]

G. Agrifoglio � R. Atencio � A. Briceno

Centro de Quımica, Instituto Venezolano de Investigaciones

Cientıficas (IVIC), Apartado 21827, Caracas 1020, Venezuela

123

Transition Met Chem (2008) 33:941–951

DOI 10.1007/s11243-008-9123-6

Experimental

General material and procedures

All materials were commercial and used without further

purification unless otherwise noted. All solvents were dis-

tilled, acetonitrile over CaH2, ether and THF over sodium

wire, stored over 4 A molecular sieves and thoroughly

degassed prior to use. All experiments were carried out

under inert atmosphere (dry nitrogen or argon) using

modified Schlenk techniques. 4,40-di-tert-butyl-2,20-bipyridine, 4,40-dimethoxy-2,20-bipyridine and bis(3,5-

dimethylpyrazol-1-yl)methane were synthesized using lit-

erature methods. NMR spectra were recorded on a Bruker

AVANCE 500 MHz spectrometer. IR spectra were recor-

ded on a Perkin Elmer 1720 XFT spectrometer.

Crystal structure determination

Intensity data for the compounds 1, 6 and 7 were recorded at

room temperature on a Rigaku AFC-7S diffractometer using

monochromated Mo(Ka) radiation (k = 0.71073 A).

Experimental details on unit cell and intensity measurements

can be found in the CIF files deposited with the Cambridge

Crystallographic Data Centre (68693, 68694 and 68695).

Crystal data, intensity data collection parameters and final

refinement results are summarized in Table 1. The structures

were solved by Direct Methods and refined by full-matrix

least-squares on F2. The H-atoms on C were placed in cal-

culated positions using a riding atom model with fixed C–H

distances [0.93 A for C(sp2), 0.96 A for C(sp3, CH3) and

0.97 A for C(sp3, CH2)]. All the H atoms were refined with

isotropic displacement parameters set to 1.2 9 Ueq for

Table 1 Crystal data, intensity

data collection parameters and

final refinement results

Compound 1 6 7

CCDC deposit no.

Crystal data

Formula C54H54MoN2O4Si � CH2Cl2 C11H16Cl2MoN4O2 C11H16Br2MoN4O2

Mw 1032.4 403.12 492.04

Specimen size (mm) 0.38 9 0.14 9 0.12 0.60 9 0.48 9 0.20 0.46 9 0.22 9 0.17

T (K) 293 (2) 293 (2) 293 (2)

a (A) 11.222 (6) 10.2723 (14) 10.500 (2)

b (A) 17.645 (6) 14.2462 (12) 14.307 (3)

c (A) 26.376 (6) 10.9094 (12) 11.103 (2)

b (�) 96.60 (3) 107.019 (9) 106.47 (3)

V (A3) 5188 (3) 1526.6 (3) 1595.5 (3)

Crystal system Monoclinic Monoclinic Monoclinic

Space group P21/n P21/n P21/n

Z 4 4 4

Dc (c cm-3) 1.321 1.754 2.043

l (mm-1) 0.45 1.22 5.82

Number of ref. for cell 20 25 2,372

Data collection

H Range (�) 26.0–26.8 22.6–25.3 2.3–28.0

h 0, 13 0, 12 -9, 12

k 0, 20 0, 16 -16, 16

l -31, 31 -12, 12 -13, 14

Number of ref. measured 9,603 2,487 18,255

Number of ref. unique 9,102 2,275 3,078

Ref. I [ 2r(I) 4,933 2,493 2,686

Rint 0.051 0.083 0.031

Refinement

R[F2 [ 2r(F2)] 0.069 0.027 0.035

wR(F2) 0.165 0.076 0.087

S 1.00 1.11 1.11

No. param. Refin. 600 185 185

(D/r) max. 0.001 0.001 0.001

Dq (min., max) (eA-3) -0.64, -0.48 -0.78, 0.73 -0.86, 0.44

942 Transition Met Chem (2008) 33:941–951

123

C(sp2) and 1.5 for C(sp3) of the attached atom. In the struc-

ture 1, the dichloromethane molecule was found to be

disordered. This disorder was modelled over three orienta-

tions with restraints in the C–Cl and Cl–Cl distances and

complementary occupancies. The occupational parameters

were refined and fixed during the final refinement cycle in

40:40:20. Only these atoms were refined with isotropic dis-

placement parameters. Data reduction for 1 and 6 were

performed using teXsan [10], whereas 7 was made using the

Crystal clear [11] crystallographic software packages,

respectively. All the refinement calculations were made

using SHELXTL-NT [12].

4,40-dichloro-2,20-bipyridine

A suspension of 4,40-dinitro-2,20-bipyridine-1,10-dioxide

[13] (1.5 g, 5.4 mmole) in 60 mL of acetyl chloride was

refluxed, under inert atmosphere, for 4 h. The reaction

mixture was cooled in an ice bath and to it was slowly

(15 min) added 15 mL of freshly distilled PCl3. The

resulting mixture was refluxed for an additional 4 h and the

volume reduced under vacuum to 20–30 mL. The solution

was cooled in an ice bath and slowly poured into 200 g of

crushed ice then made alkaline with NaOH. The precipitate

was filtered off and the product extracted with CH2Cl2,

dried over MgSO4 and recrystallized from ethanol/water.1H-NMR (CDCl3); d 7.39(dd), 8.40(d), 8.55(d).

Mo(O)2(4,40-t-butyl-2,20-bipy)(OSiPh3)2 � 1

To a 15 mL CH3CN solution of 4,40-di-tert-butyl-2,20-bipyridine (0.134 g, 0.5 mmol) was added 0.103 g

(0.5 mmol) of anhydrous Na2MoO4. The suspension was

stirred at 25 �C for 30 min before 0.265 g (0.9 mmol) of

triphenylchlorosilane was added. The resulting mixture

was heated to reflux for a period of 5 h and evaporated to

dryness. The white solid obtained was extracted with

CH3CN (3 9 10 mL). Removal of the solvent gave the

desired compound as a white crystalline solid. Yield

0.40 g, 93%. IR (KBr): m(Mo=O) 934(s), 910(sh); m(Si–O)

1,113(s) cm-1. 1H-NMR (CDCl3): d 1.41 (s), 7.1–7.3 (m),

7.43 [dd, J(H–H) = 6 Hz, 1.6 Hz], 7.75 [dd, J(H–H) =

6 Hz, 1.6 Hz], 9.03 [dd, J(H–H) = 6 Hz, 1.6 Hz]. Anal.

Calcd. for C54H54N2O4Si2Mo; C, 68.47; H, 5.75; N, 2.96.

Found; C, 68.58; H, 5.67; N, 2.87.

Mo(O)2 [bis(3,5-Me2-pyrazolylmethane)](OSiPh3)2 � 2

To a 25 mL CH3CN solution containing 0.296 g

(1.45 mmol) of bis-(3,5-Me2-pyrazolylmethane was added

0.299 g (1.45 mmol) of anhydrous Na2MoO4. The sus-

pension was stirred at 25 �C for 30 min and 0.740 g

(2.90 mmol) of triphenylchlorosilane was added. The

mixture was refluxed for 4 h and the resulting yellowish

suspension was evaporated to dryness, and extracted with

CH2Cl2 (2 9 50 mL). Evaporation gave a colourless

crystalline solid. Yield 1.16 g, 91%. IR(KBr): m(Mo=O)

929(m), 907(m) cm-1, m(Si–O) 1,118(s) cm-1. 1H-NMR

(CDCl3); d 2.40 (s), 2.65 (s), 5.95 (s), 6.50 (s), 7.1–7.3(m).

Anal. Calcd. for C47H46N4O4Si2Mo; C, 63.93; H, 5.25; N,

6.34. Found; C, 64.05; H, 5.28; N, 6.28.

Mo(O)2(4,40-t-butyl-2,20-bipy)Cl2 � 3

To a 15 mL CH3CN solution containing 134 mg (0.5 mmol)

of 4,40-di-t-butyl-2,20-bipyridine was added 103 mg

(0.5 mmol) of anhydrous Na2MoO4. The suspension was

stirred 30 min at room temperature and to it was added

216 mg (250 lL, 2 mmole) of trimethylchlorosilane. The

mixture was refluxed for 4 h and reduced to dryness under

vacuum to give a colourless solid residue. Recrystallization

from CH2Cl2/n-hexane (2/1) yielded a colourless crystalline

solid. Yield 0.22 g, 94%. IR (KBr); m(Mo=O), 939(s), 908(s)

cm-1. 1H-NMR (CDCl3) d 7.70 [dd, J(H–H) = 6 Hz,

1.6 Hz], 8.16 [d, J(H–H) = 6 Hz], 9.47 [d, J(H–H) =

6 Hz]. Anal. Calcd. for C18H24N2O2Cl2Mo; C, 46.27; H,

5.18; N, 5.99. Found; C, 46.12; H, 5.16; N, 6.12.

Mo(O)2(4,40-(OCH3)-2,20-bipy)Cl2 � 4

A 20 mL CH3CN suspension containing 21 mg (0.1 mmole)

of anhydrous Na2MoO4 and 22 mg (0.1 mmole) of 4,40-dimethoxy-2,20-bipyridine was stirred overnight at room

temperature. To the resulting white suspension was added

46.5 mg (53.5 lL, 0.42 mmole) of Me3SiCl; it resulted

immediately in the intensification of the white suspended

material. The mixture was refluxed for 4 h and evaporated

under vacuum to give a white solid. Treatment with CH2Cl2(2 9 30 mL) led to only partial extraction; it was slightly

improved by refluxing the solid in CH2Cl2 and filtering while

hot, but the overall yield remained modest (60%). Never-

theless, the complex obtained was quite pure. Yield 25 mg,

60%. IR (KBr); m(Mo=O) 937(s), 906(s) cm-1. 1H-NMR

(CD2Cl2); d 4.05(s), 7.20 [dd, J(H–H) = 6 Hz, 1.6 Hz], 7.67

[d, J(H–H) = 6 Hz], 9.32 [d, J(H–H) = 6 Hz]. Anal. Calcd.

for C12H12N2Cl2O4Mo; C, 41.87; H, 3.51; N, 8.14. Found; C,

41.79; H, 3.55; N, 8.20.

Mo(O)2(4,40-Cl-2,20-bipy)Cl2 � 5

A 30 mL suspension containing 51.5 mg (0.25 mmole) of

anhydrous Na2MoO4 and 56.2 mg (0.25 mmole) of 4,40-dichloro-2,20 bipyridine was stirred overnight at room tem-

perature. To the resulting suspension was added 108 mg

(125 lL, 1 mmole) of Me3SiCl. The mixture was refluxed

for 4 h and evaporated to dryness under vacuum. Extraction

Transition Met Chem (2008) 33:941–951 943

123

of the desired product with CH2Cl2 was incomplete, hot

acetone was used instead to give a white solid upon evapo-

ration of the solvent. Yield calculated with two moles of

acetone, 78 mg, 65%. IR (KBr); m(Mo=O) 944(s), 915(s)

cm-1. 1H-NMR (d6 acetone) d 8.10 [dd, J(H–H) = 6 Hz,

1.6 Hz], 8.98 [d, J(H–H) = 6 Hz], 9.46 [d, J(H–H) =

6 Hz]. Anal. Calcd. for C10H6N2Cl4O2Mo + 2 (CH3)2CO;

C, 32.3; H, 2.5; N, 5.8. Found; C, 31.4; H, 2.3; N, 5.6.

Mo(O)2 [bis(3,5-Me2-pyrazolylmethane)]Cl 2 � 6

To a 25 mL CH3CN solution containing 0.296 g

(1.45 mmol) of bis-(3,5-Me2-pyrazolylmethane was added

0.299 g (1.45 mmol) of anhydrous Na2MoO4. After stirring

the suspension for 30 min, 0.630 g (733 lL, 5.8 mmol) of

trimethylchlorosilane was added and the mixture heated to

reflux for 4 h. Evaporation to dryness gave a white solid

(yield 0.54 g, 92%) which upon recrystallization from

CH2Cl2/n-hexane (2/1) gave the desired product as a col-

ourless crystalline solid. IR (KBr); m(Mo=O) 943(s), 910(s)

cm-1. 1H-NMR (CDCl3); d 2.45 (s), 2.75 (s), 6.01 (s), 6.56

(s). Anal. Calcd. for C11H16N4O2Cl2Mo; C, 32.77; H, 4.00;

N, 13.64. Found; C, 32.39; H, 3.86; N, 13.51.

Mo(O)2 [bis-(3,5-Me2-pyrazolylmethane)]Br2 � 7

A 25 mL CH3CN suspension containing 204 mg (1 mmol)

of bis-(3,5-Me2-pyrazolylmethane) and 206 mg (1 mmol)

of anhydrous Na2MoO4 was stirred for 30 min at room

temperature. To the resulting milky suspension was added

612 mg (430 lL, 4 mmol) of trimethylbromosilane and the

mixture refluxed for 4 h. Evaporation of the solvent gave a

yellow-green solid which was extracted with CH2Cl2(2 9 30 mL). Evaporation gave nearly pure product. Yield

0.47 g, 96%. Recrystallization from CH2Cl2/n-hexane (2/1)

gave an X-ray suitable material. IR (KBr) n(Mo=O), 941,

907 cm-1. 1H-NMR (CDCl3); d 6.53(s), 6.06(s), 2.73(s),

2.43(s). Anal. Calcd. for C11H16N4Br2Mo; C, 27.59; H,

3.24; N, 11.38. Found; C, 26.72; H, 3.26; N, 11.22.

Mo(O)2(t-butyl-bipy)(NCS)2 � 8

To a 15 mL CH3CN solution containing 134 mg (0.5 mmole)

of 4,40-di-t-butyl-2,20-bipyridine was added 103 mg

(0.5 mmole) of anhydrous Na2MoO4. The resulting suspen-

sion was stirred at room temperature for 30 min and to it was

added 263 mg (282 lL, 2 mmole) of Me3SiNCS. The mix-

ture became quickly yellow. It was refluxed for 4 h, turning

reddish. After evaporation to dryness, the resulting red solid

was extracted with CH2Cl2 (2 9 50 mL). Evaporation of the

solvent yielded nearly pure product. Yield 0.24 g, 95%. IR

(KBr): m(Mo=O) 935(s), 905(s), m(SCN) 2,014(vs) cm-1.1H-NMR (CDCl3) d 7.77 [dd, J(H–H) = 6 Hz, 1.6 Hz], 8.22

[d, J(H–H) = 6 Hz], 9.35 [d, J(H–H) = 6 Hz]. Anal. Calcd.

for C20H24N4S2O2Mo; C, 46.87; H, 4.72; N, 10.93; S, 12.51.

Found; C, 46.62; H, 4.69; N, 11.00; S, 12.46.

[Mo(O)2(t-butyl-bipy)(NCS)]2O � 9

A 25 mL CH3CN suspension containing 103 mg (0.5 mmole)

of anhydrous Na2MoO4 and 134 mg (0.5 mmole) of 4,40-di-t-

butyl-2,20-bipyridine was stirred overnight at room tempera-

ture. To the white milky suspension obtained was added

196 mg (210 mL, 1.5 mmole) of Me3SiNCS. The mixture

became quickly yellow, it was kept at room temperature for

1 h and then refluxed for 3 h. The yellow suspension was

evaporated under vacuum and the solid extracted with CH2Cl2(2 9 30 mL). Evaporation of the solvent afforded 220 mg of

pure product (94%). IR (KBr): m (Mo=O) 937(s), 907(s), m(Mo–O–Mo), 776(s). 1H-NMR identical with an authentic

sample [14]. 1H-NMR (CDCl3) d 1.36(s); 1.41(s); 1.43(s);

1.48(s); 7.45 [d, J(H–H) = 6 Hz], 7.57 [d, d, J(H–H) =

6 Hz, 1.6 Hz], 7.69 [t, J(H–H) = 6 Hz]; 7.98 [d, J(H–H) =

6 Hz]; 8.14 [d, J(H–H) = 1.6 Hz], 8.24 [d, J(H–H) = 6 Hz];

8.51 [d, J(H–H) = 6 Hz]; 8.78 [d, J(H–H) = 6 Hz]; 8.89

[d, J(H–H) = 6 Hz]; 9.36 [d, J(H–H) = 6 Hz], 9.406 [d,

J(H–H) = 6 Hz].

W(O)2(t-butyl-bipy)(NCS)2 � 11

To a 20 mL CH3CN solution containing 134 mg

(0.5 mmole) of 4,40-di-t-butyl-2,20-bipyridine was added

147 mg (0.5 mmole) of anhydrous Na2WO4. The suspen-

sion was stirred 30 min at room temperature and to it was

added 263 mg (282 lL, 2 mmole) of Me3SiNCS. The

mixture was refluxed for 4 h and the resulting suspension

evaporated to dryness. Extraction of the resulting solid with

CH2Cl2 (2 9 30 mL) followed by evaporation gave a

white solid. Yield 0.26 g, 87%. IR (KBr) m(W=O): 952(s),

912(s), m(SCN): 2,016 cm-1. 1H-NMR (CDCl3) d 1.50(s),

7.80 [dd, J(H–H) = 6 Hz, 1.6 Hz]; 8.20 [d, J(H–

H) = 6 Hz], 9.12 [d, J(H–H) = 6 Hz]. Anal. Calcd. for

C20H24N4S2O2W: C, 40.01; H, 4.03; N, 9.32; S, 10.68;

Found: C, 40.50; H, 4.15; N, 9.05; S, 10.65.

ReO3[bis-(3,5-Me2-pyrazolylmethane)]Cl � 12

A 40 mL CH3CN suspension containing 289 mg

(1 mmole) of KReO4 and 204 mg (1 mmole) of bis-(3,5-

dimethyl-pyrazol-1-yl)methane was stirred at room tem-

perature for 24 h. To the milky mixture obtained was added

217 mg (186 lL, 2 mmole) of trimethylchlorosilane and

refluxed for an additional 24 h. The resulting white sus-

pension was filtered. Evaporation of the filtrate under

vacuum yielded a low melting solid free of any unreacted


123

ligand. Yield 0.37 g, 78%. IR (KBr) m(Re=O): 912 (s), 840

(m). 1H-NMR (CDCl3) d 6.39(s), 5.98(s), 2.47(s), 2.20(s).

Results and discussion

The one-pot procedure consists of reacting sodium

molybdate with the halosilane, in the appropriate stoichi-

ometry, in the presence of a bidentate ligand in acetonitrile.

Simple evaporation of the solvent at the end of the reaction

and separation from the sodium halide by-product, gives

the desired complex in high yield. The success of the

method is plausibly linked to the coordinating properties of

acetonitrile, since no other media allows the reaction to

work.

Siloxylation of Na2MoO4 with Ph3SiCl proceeds

in a manner analogous to the reported reaction

with K2WO4 [9]

With 4,40-di-t-butyl-2,20-bipyridine � 1

The acetonitrile solution containing bipyridine and triphe-

nylchlorosilane reacts readily with the molybdate salt in

suspension, to yield the colourless crystalline dioxo com-

plex upon straightforward work up. It shows two intense

Mo=O infrared bands at 956 and 905 cm-1 and one Si–O

stretch at 1,113 cm-1. The 1H-NMR spectrum is typical of

a species with a C2 symmetry with one single pattern for a

pyridyl ring (d 8.9, 7.6, 7.3) as well as a unique tert-butyl

resonance peak (d 1.34). As expected the complex exhibits

high stability towards moisture or air. Its structure was

confirmed by an X-ray spectroscopic analysis (Fig. 1).

With bis(3,5-dimethylpyrazol-1-yl)methane � 2

As in the case of the reaction with 4,40-t-butylbipyridine,

the reaction mixture in acetonitrile is a suspension and

yields the expected dioxo complex upon work up. The

yield is very much dependent on the dryness of the starting

molybdate salt. The infrared spectrum shows two intense

bands at 929 and 907 cm-1 for m Mo=O and one for m Si–O

at 1,118 cm-1. The 1H-NMR indicates again clearly a C2

symmetry with only one pyrazolyl pattern. Following an

identical procedure with both ligands is a good indication

of the general character of this method.

The simple one-pot procedure used for the silyloxylation

reaction with Na2MoO4 brought us to consider its exten-

sion to chlorination by the use of trimethylchlorosilane.

This would render easily accessible the synthesis of dioxo-

dichloro complexes and add a real versatile character to

this synthetic method. We tried, at first, the reaction with

molybdate ion in the presence of four different bidendate

ligands.

Chlorination of Na2MoO4 with Me3SiCl


The procedure followed was analogous to the silylation

reaction with triphenylchlorosilane, except that four

equivalents of Me3SiCl were used instead of two. The

Fig. 1 Mo(O)2(4,40-t-butyl-

2,20-bipy)(OSiPh3)2. 1 The

displacement parameters are

drawn at 30% probability


123

heterogeneous reaction mixture in acetonitrile after reflux

and work up yielded a colourless crystalline solid. It

showed in infrared spectroscopy two strong absorption

bands at 908 and 939 cm-1 attributed to m Mo=O, as well

as those corresponding to the bipyridyl moiety. No

absorption corresponding to m Si–O were observed. The1H-NMR spectrum displays one single set of signals for the

bipyridyl ligand at d 9.47, 8.16 and 7.70 well in accord

with a C2 symmetry. All these values are identical with

those obtained for the same dichloro-dioxoMo(VI) com-

plex prepared by another synthetic route [13]. Its X-ray

structure has been reported previously [13].

With 4,40-dimethoxy-2,20-bipyridine [15] � 4

The reaction was run with four equivalents of Me3SiCl

following an analogous procedure as for the 4,40-t-butyl-

2,20-bipyridine ligand. The white solid exhibited in IR

spectroscopy two absorption bands characteristic of mMo=O at 937 and 906 cm-1. The 1H-NMR in CD2Cl2,

showed a typical set of signals for a bipyridyl entity in

accord with a C2 symmetry at d 9.32, 7.67 and 7.20 for the

aromatic hydrogen and at d 4.05 for the methoxy group. It

should be noted that the synthesis of this same complex

was attempted with the multistep reported procedure [13],

yielding a mixture of the desired product contaminated

with a dimeric species, and thus, was not reported.

With 4,40-dichloro-2,20-bipyridine � 5

Under analogous reaction conditions and upon work up, a

white solid was obtained. The extraction with CH2Cl2 was

unsatisfactory, it was repeated with hot acetone which upon

evaporation gave a white solid. The infrared spectroscopy

(m Mo=O, 944,950 cm-1) as well as the 1H-NMR (d6

acetone) (d 9.50, 8.21, 7.77) were in accord with the pure

desired complex.


As in the case of the 4,40-di-t-butyl-2,20-bipyridine ligand

the reaction proceeded as a heterogeneous suspension and

yielded upon work up a white crystalline product exhibit-

ing in infrared spectroscopy two sharp absorption bands at

943 and 910 cm-1 (m Mo=O). The 1H-NMR analysis

showed a pattern for the pyrazolyl ring corresponding to a

complex having a C2 symmetry at d 6.56, 6.01, 2.75 and

2.45. Interestingly, the downshift expected upon com-

plexation is less with this ligand than the downshift

observed for 4,40-di-t-butyl-2,20-bipyridine; this is in

agreement with the slight difference observed in infrared

spectroscopy. Its structure was confirmed by an X-ray

spectroscopic analysis (Fig. 2).

Bromination of Na2MoO4 with Me3SiBr


The use of trimethylbromosilane as a brominating agent for

metal-oxo compounds is less common, it was of great

interest to compare this halogenation method and extend it

to the bromination of sodium molybdate. The reaction

proceeds as a heterogeneous mixture in a manner analo-

gous to the chlorination reaction and yields upon work up a

light green solid exhibiting in infrared spectroscopy two

strong absorption bands at 907 and 941 cm-1 attributed to

m Mo=O. The 1H-NMR analysis showed resonance peaks

for the pyrazolyl ligand at 6.53, 6.06, 2.73 and 2.43 ppm.

The IR and NMR values are quite close to the chloro

analogue showing very little difference when varying the

halogen. This was already observed with the bidentate

ligand 4,40-t-butyl-2,20-bipyridine [13]. Its structure was

confirmed by an X-ray spectroscopic analysis (Fig. 3).

Thiocyanation of Na2MoO4 with Me3SiNCS


Dithiocyanato-dioxo-4,40-di-t-butyl-2,20-bipyridine

Mo(VI) has been previously reported [15] and its synthesis

and reactivity as an oxo transfer agent largely studied. It

was of interest to check if it could be prepared by the

present more direct and easier method. Under analogous

reaction conditions as in the case of halogenation, the

Fig. 2 Mo(O)2 [bis(3,5-Me2-pyrazolylmethane)]Cl2. 6 The displace-

ment parameters are drawn at 30% probability


123

heterogeneous mixture yielded upon work up the desired

complex in nearly quantitative yield exhibiting the IR and

NMR properties previously reported [15].

In the above halogenation or thiocyanation reactions,

two plausible pathways can be considered as shown

below.

When depicted stepwise, the first two moles of halosi-

lane give (1) which upon loss of hexamethyldisiloxane,

yield the trioxo intermediate (2). With the third mole of

halosilane the formation of (3) is most likely. Intermediate

(3) can now possibly follow two different routes.

Either the fourth mole of halosilane adds to (3) to give

(4) which upon loss of hexamethyldisiloxane yields the end

product (5), or two moles of (3) can spontaneously rear-

range to form the l-oxo-dimer (6) accompanied by the loss

of one mole of hexamethyldisiloxane. Complex (6), in turn

can undergo the addition of the fourth mole of halosilane,

before being transformed to the end product (5).

If the second route is operative, it is conceivable to stop

the reaction when (6) is formed simply by changing the

overall stoichiometry Na2MoO4/Me3SiX from 1/4 to 1 /3.

This is indeed what was observed. When sodium molyb-

date was treated with three equivalent mole of Me3SiNCS

in the presence of 4,40-di-t-butyl-2,20-bipyridine, one

obtains as sole product the previously reported [14] and

well-characterized l-oxo-dioxo-thiocyanatoMo(VI) com-

plex 9 with a high degree of purity.

This pathway was further corroborated by reacting the

isolated pure l-oxo dimer complex with two equivalents of

Me3SiNCS to give the expected dithiocyanato-dioxo-

Mo(VI) compound 8 in quantitative yield.

Fig 3 Mo(O)2 [bis-(3,5-Me2-pyrazolylmethane)]Br2. 7 The displace-

ment parameters are drawn at 30% probability

Mo

OO

O

Mo

MoMoMo

Mo

(6) (5)

(5)(4)

(3)

(3)

(3)(2)(1)

(1)

2

X

X

L

O

O

{(CH 3 ) 3Si] 2 O

2 (CH 3) 3 SiX

{(CH 3) 3Si] 2O

L

L

Mo-XO

O

X-Mo2

X

(CH 3) 3SiO

L

O

O

X

X

L

O

O

{(CH 3) 3 Si] 2O

OSi(CH3) 3(CH 3) 3SiO

L

XX

O

(CH 3) 3SiX

X

(CH 3) 3SiO

L

O

O

X

(CH 3) 3SiO

L

O

O

(CH 3) 3SiX

(CH 3) 3SiX

L

O

O

O Mo

{(CH 3) 3Si] 2O

O

O

L

[(CH 3) 3SiO] 2Mo

+ 2 X -O

O

L

[(CH 3) 3SiO] 2Mo+ L + 2 -2

MoO4


123

Although this last reaction, as such, is somewhat limited

from a practical point of view, it suggests, nevertheless, a

possible new synthetic route in which two different halo-

gens or pseudo halogens could be bonded to the dioxo-

Mo(VI) centre. Indeed, reacting a given l-oxo-dioxo

molybdenum(VI) dimer bearing one type of halogen with

trimethylsilane of another halogen, should plausibly lead to

a ‘‘mixed’’ dihalo-dioxo-Mo(VI) entity.

When [Mo(O)2(t-butyl-bipy)(NCS)]2O was reacted with

two equivalents of trimethylchlosilane, the product

obtained upon workup, showed in infrared spectroscopy

the absence of absorption band at 760 cm-1 indicating that

no l-oxo dimeric species remained. The rest of the spec-

trum was in accord with a typical molybdenum(VI) dioxo

complex with a C2 symmetry. The 1H-NMR analysis, on

the other hand, showed a pattern corresponding to three

distinct bipyridyl moieties integrating to approximately

0.5/1/0.5. The chemical shifts of the two minor species

correspond, respectively, to values for the dichloro and

dithiocyanato dioxo complexes, whereas the third bipydyl

set resonates at values just intermediate as is shown in

Fig. 4. This observation might be interpreted in terms of

the ‘‘mixed’’ complex 10 being indeed formed as the major

product but, unfortunately, accompanied by a scrambling

phenomenon via a probable equilibrium step [2], leading to

a mixture of dioxo-dichloro 3 and dioxo-dithiocyanato 8

species.

Chlorination of Na2WO4 with Me3SiNCS


This one-pot halogenation and thiocyanation of molyb-

date ion has been extended to tungstate ions. We

reported recently [16] the chlorination of sodium tung-

state in the presence of 4,40-di-t-butyl-2,20-bipyridine.

The thiocyanation of sodium tungstate was shown also to

be effective by this simpler route using trimethylthiocy-

anatosilane to give as for the molybdate ion the

corresponding dithiocyanatodioxotungstate(VI) recently

reported [16].

ButBut

NNOO

NNOO

OCH3CN

+ 6 (CH3) 3SiNCS2 Na2MoO42+ Mo-NCSSCN-Mo

NN

O

OO

NNOO

2CH3CN

2 (CH3)3SiNCS+ (SCN)2Mo=O

NN

O Mo-NCSSCN-Mo

NN

O

OO

NNO

Mo=OY

X2

NN

+ 2 (CH3)3Si-YCH3CN

X-Mo Mo-XO

O

NN


123

Chlorination of KReO4 with Me3SiCl


Chlorination of the rhenium-oxo function with trimethyl-

chlorosilane is a well known reaction [1, 17–20]. It is

mainly encountered as an intermediate step in the synthesis

of alkyl rhenium-oxo species or halo rhenium-oxo com-

plexes bearing bidentate N-ligands. The most common

rhenium(VII) oxide used is Re2O7, although more recently

HReO4 was reported [20] as the source of rhenium-oxo for

the synthesis of a chloro rhenium trioxo complex stabilized

by two molecules of THF. It was of interest to test the

present simple, one-pot synthetic procedure with potassium

perrhenate. The reaction was performed in the presence of

the N-bidentate ligand bis(3,5-dimethylpyrazol-1-yl)meth-

ane, and shown to be as effective as with molybdate or

tungstate salts.

X-ray analysis

Figures 1–3 show an ORTEP representation of the

molecular structure of compounds 1, 6 and 7 in the solid

Fig. 4 1H-NMR spectrum:

3 = Cl2Mo(O)2-t-butyl-bipy,

10 = Cl(NCS)Mo(O)2-t-butyl-

bipy, 8 = (NCS)2Mo(O)2-t-

butyl-bipy

N

N

N

N

L =

L-ReO 3Cl + Me3SiOSiMe3 + KCl

CH3CNKReO4 + 2 Me3SiCl + L

ButBut

NNNCS

OOCH3CN

+ 4 (CH3) 3SiNCSNa2WO4 + SCN-W

NN


123

state as determined by single-crystal X-ray diffraction

studies. The crystallographic data for the complexes are

given in Table 1 and selected bond lengths and angles are

in Table 2.

The molecular structure of 1 consists of a discrete

molecule where the central molybdenum atom binds to two

O atoms of the siloxy ligands, two nitrogen atoms of the

chelate substituted bipy and two oxygen atoms of oxo-type

and exhibits a distorted octahedral geometry. Thus, the

bond angles around the metal vary from 68� for the donor

atoms of bipy, 107� for the oxo ligands and 79� for the

siloxy groups. Meanwhile, in the distorted octahedral

geometry for the complexes 6 and 7, the bond angles vary

from 79� for the nitrogen atoms of the pyrazolyl chelate,

104� for the oxo ligands and 96� for the halogen ligands.

The bond lengths and angles of the MoO2(4,40-tBu-2,20-bipy)(OSiPh3)2 moiety do not vary significantly and are

comparable to those found in other molybdenum com-

pounds with the same units and geometry [21].

The two pyrazolyl rings have good planarity, with

maximum deviations from the mean planes of less than

0.009 A. The metallacycle C–N1–N2–N3–N4–Mo usually

has boat conformation, for the complex 6 and 7 we found

the boat conformation are very asymmetric, with the

dihedral angle: N1–N2–N3–N4 and N2–C6–N3 of 71.4�and N1–N2–N3–N4 with N1–Mo1–N4 of 16.2� for the

complex 6. For the complex 7 we have dihedral angle of

14.9� and 73.1�, respectively. Both complexes have a

quasi-sofa conformation [22]. For these compounds in

general, the values of bond lengths and angles are within

the expected values [23, 24].

Acknowledgements This work was done under the auspices of the

project ECOS-Nord France-Venezuela and Fundayacucho. Financial

support is kindly acknowledged.

References

1. Hermann WA (1988) Angew Chem Int Ed Engl 27:1297

2. Parkin G, Bercaw JE (1989) J Am Chem Soc 111:391

3. Nugent WA, Mayer JM (1983) Metal-ligand multiple bonds.

Wiley-Interscience, New York

4. Arzoumanian H, Krentzien H, Corao C, Lopez R, Agrifoglio G

(1995) Polyhedron 14:2887

5. Lorber C, Donahue JP, Goddard CA, Nordlander E, Holm RH

(1998) J Am Chem Soc 120:8102

6. Teruel H, Gorrin YC, Falvello LR (2001) Inorg Chim Acta 316:1

7. Huang M, DeKock CW (1993) Inorg Chem 32:2287

8. Thapper A, Donahue JP, Musgrave KB, Willer MW, Nordlander

E, Hedman B, Hodgson KO, Holm RH (1999) Inorg Chem

38:4104

9. Miao M, Willer MW, Holm RH (2000) Inorg Chem 39:2843

10. Molecular Structure Corporation (1999) TEXSAN. Single crystal

structure analysis software, version 1.10. MSC, 9009 New Trails

Drive, The Woodlands, TX 77381-5209, USA

11. Rigaku/MSC, Inc. (2000) CRYSTALCLEAR, Software users

guide, version 1.3.6, The Woodlands, TX, USA

12. Bruker (1998) SHELXTL-NT, version 5.1 Bruker AXS Inc.,

Madison, WI, USA

13. Arzoumanian H, Bakhtchadjian R, Agrifoglio G, Atencio R,

Briceno A (2006) Trans Met Chem 31:681

14. Arzoumanian H, Bakhtchadjian R, Agrifoglio G, Krentzien H,

Daran JC (1999) Eur Inorg Chem 2255

15. Arzoumanian H, Maurino L, Agrifoglio G (1997) J Mol Catal A

Chem 117:471

16. Arzoumanian H, Agrifoglio G, Capparelli M, Atencio R, Briceno

A, Alvarez-Larena A (2006) Inorg Chim Acta 359:81

17. Herrmann WA, Thiel WR, Herdtweck E (1990) Chem Ber

123:271

Table 2 Selected bond lengths

(A´

) and angles (�)Compound 1 Compound 6 Compound 7

Mo1–O1 1.695 (4) Mo1–O2 1.683 (2) Mo1–O2 1.684 (3)

Mo1–O2 1.696 (4) Mo1–O1 1.684 (2) Mo1–O1 1.686 (3)

Mo1–O3 1.921 (4) Mo1–Cl2 2.351 (8) Mo1–Br2 2.5067 (7)

Mo1–O4 1.927 (4) Mo1–Cl1 2.3773 (7) Mo1–Br1 2.5399 (8)

Mo1–N2 2.345 (5) Mo1–N1 2.356 (2) Mo1–N1 2.363 (3)

Mo1–N1 2.348 (5) N1–C1 1.337 (3) Mo1–N4 2.355 (3)

Si1–O4 1.600 (4) N2–C6 1.442 (3) Mo1–N1 2.363 (3)

Si2–O3 1.604 (4)

O1–Mo1–O2 107.2 (2) O2–Mo1–O1 103.72 (11) O2–Mo1–O1 103.61 (16)

O1–Mo1–O3 97.3 (2) O2–Mo1–N1 168.14 (10) O1–Mo1–N4 167.83 (14)

O2–Mo1–O3 97.3 (2) N1–Mo1–N4 78.99 (7) N4–Mo1–N1 79.32 (11)

O3–Mo1–O4 154.28 (18) Cl2–Mo1–Cl1 162.07 (3) Br2–Mo1–Br1 162.73 (2)

O1–Mo1–N2 92.5 (2) N2–N1–Mo1 125.32 (15) N2–N1–Mo1 126.0 (2)

O2–Mo1–N2 160.3 (2) O2–Mo1–Cl1 94.19 (9) O2–Mo1–Br2 96.84 (10)

Si1–O4–Mo1 179.7 (3) C1–N1–N2 105.5 (2) O2–Mo1–N4 88.51 (13)

Si2–O3–Mo1 175.3 (3)


123

18. Herrmann WA, Kuhn FE, Romao CC, Kleine M, Mink J (1994)

Chem Ber 127:47

19. Kuhn FE, Haider JJ, Herdtweck E, Herrmann WA, Lopes AD,

Pillinger M, Romao CC (1998) Inorg Chim Acta 279:44

20. Noh W, Girolami GS (2007) J Chem Soc Dalton Trans 674

21. Thapper A, Donahue JP, Musgrave KB, Miller MW, Nordlander E,

Hedman B, Hodgson KO, Holm RH (1999) Inorg Chem 38:4104

22. Agrifoglio G, Capparelli M (2005) J Chem Crystallogr 35:95

23. Pettinari C, Pettinari R (2005) Coord Chem Rev 249:663

24. Santos AM, Kuhn FE, Bruns-Jensen K, Lucas I, Romao CC,

Herdtweck E (2001) Dalton Trans 1332


123

A one-pot synthesis of disiloxy, dihalo and dithiocyanato dioxo complexes bearing a bidentate...

Documents

Transcript of A one-pot synthesis of disiloxy, dihalo and dithiocyanato dioxo complexes bearing a bidentate...