Russian Chemical Bulletin, International Edition, Vol. 62, No. 1, pp. 147—156, January, 2013 147

Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0149—0158, January, 2013.

1066�5285/13/6201�147 © 2013 Springer Science+Business Media, Inc.

Stable organomercury compounds containingan o�iminosemiquinone radical ligand

A. V. Piskunov,a I. N. Meshcheryakova,a I. V. Smolyaninov,b G. K. Fukin,a V. K. Cherkasov,a and G. A. Abakumova

aG. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.

Fax: +7 (831) 462 7497. E�mail: pial@iomc.ras.rubSouthern Scientific Center, Russian Academy of Sciences,16 ul. Tatishcheva, 414025 Astrakhan, Russian Federation.

Fax: +7 (851 2) 25 0923. E�mail: thiophen@mail.ru

A series of stable paramagnetic organomercury compounds containing the 4,6�di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzosemiquinone ligand (imSQ) with the generalformula imSQHgR (R = Ph, Et, Prn, Bun, Pri, Hexc, CH2SiMe3, p�FPh, Fc, p�Me2NPh) weresynthesized. The molecular and electronic structures of the synthesized compounds were inves�tigated by EPR spectroscopy and X�ray diffraction. The o�iminosemiquinone ligand shows theunusual amidophenoxy�type coordination mode. In the EPR spectra of the compoundsimSQHgR, the hyperfine coupling constant of magnetic mercury isotopes (199,201Hg) dependson the nature of the substituent R, the temperature, and the nature of the solvent. Voltammetricinvestigations showed that the complex imSQHgFc undergoes three reversible one�electronredox steps related to the redox transformations of both the o�iminoquinone ligand and themetallocene moiety of the molecule.

Key words: paramagnetic organic ligand, organomercury compounds, EPR, X�ray dif�fraction.

It is known that o�semiquinone radical ligands canserve as spin labels in the coordination sphere of a metalatom.1 Any changes in the coordination environment ofthe metal center are reflected in the EPR spectra, thusallowing one to rapidly obtain reliable information onstructural features of complexes in solution, e.g., investi�gate the dissociation or exchange of neutral ligands, thesolvation, and the expansion or dynamics of the coordina�tion sphere.2—9 The stability of compounds containingo�semiquinone�type ligands, including their resistance tochanges in the external conditions (temperature, solvent,and so on), is of importance. Many known main�groupmetal mono�o�semiquinone complexes are unstable, whichhinders their isolation and investigation. In particular,most of the studied mercury(II) o�semiquinolate com�pounds decompose in solution already at –20 C (the moststable ones remain unchanged overnight), and they werecharacterized mainly by EPR.10—14 An interesting featureof these complexes is that the hyperfine coupling con�stants of magnetic mercury isotopes (199,201Hg) depend onthe steric properties of alkyl substituents bound to the metalatom.12 However, the structures of these paramagneticderivatives have not been studied in more detail because oftheir low stability, and the nature of this dependence re�mains unclear.

There are a few stable mercury(II) radical complexescontaining nitronyl nitroxide and nitroxide radicals, inwhich the paramagnetic ligand is linked to the metal atomby either a covalent15—17 or a donor�acceptor bond.18 Re�cently, it has been shown that the replacement of theo�benzoquinone ligand by its nitrogen�substituted analog,viz., 4,6�di�tert�butyl�N�(2,6�diisopropylphenyl)�o�imino�benzoquinone (imQ), made it possible to synthesize thestable paramagnetic phenylmercury(II) complex (1), whichwas isolated in the individual state and characterized byEPR spectroscopy and X�ray diffraction.19

It was found that compound 1 has a spin density di�stribution uncommon for this type of complexes, is cha�racterized by the unusual geometry of the ligand env�ironment of the metal center, and exhibits a dependence

Piskunov et al.148 Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013

of the hyperfine coupling constants ai(199,201Hg) on the

solvent.The present study is a continuation of the research on

the structural features of new stable mercury(II) o�imino�benzosemiquinolate complexes containing different alkyland aryl substituents at the metal atom.

Results and Discussion

Compounds 1—10 were synthesized by the metathesisreaction of the monosodium salt of o�iminobenzoquinone(imSQNa) with the organomercury reagent RHgX in tetra�hydrofuran in the absence of atmospheric oxygen andmoisture (Scheme 1). The reaction is completed in a fewminutes and is accompanied by a change in the color fromblue, which is typical of imSQNa, to emerald�green (inthe case of compound 10, to violet). Mercury(II) com�plexes (imSQHgR) 1—10 were isolated as intensely co�lored crystalline compounds.

Scheme 1

X = Cl, OAc; R = Ph (1), Et (2), Prn (3), Bun (4), Pri (5), Hexc (6),CH2SiMe3 (7), p�FPh (8), Fc (9), p�Me2NPh (10)

Like compound 1,19 all the newly synthesized com�plexes yield well�resolved EPR signals (Fig. 1) as a triplet(1 : 1 : 1) of doublets (1 : 1) attributed to the coupling ofan unpaired electron with the nitrogen atom 14N (99.63%,I = 1, N = 0.4037)20 and the proton 1H (99.98%, I = 1/2,N = 2.7928)20 at position 5 of the o�iminoquinone ring.The EPR spectra of all complexes also show a satel�lite splitting on the magnetic mercury isotopes 199Hg(17.0%, I = 1/2, N = 0.5059) and 201Hg (13.2%, I = 3/2,N = –0.5602).20

The parameters of the EPR spectra of compounds 1—10are given in Table 1. It should be noted that the distin�

guishing feature of the EPR signals for the whole series ofthe synthesized mercury o�iminosemiquinone complexesis a small value of the hyperfine coupling constant ai(

1H).This constant is, on average, 0.25 mT, whereas main�group metal o�iminobenzosemiquinone complexes arecharacterized by larger constants (~0.35 mT).21 The valueof ai(

1H) in the range of 0.18—0.20 mT is typical ofmeta�protons in phenoxyl radicals.22 This indicates that

Fig. 1. Isotropic EPR spectrum of complex 10 in hexane (1),THF (2), and pyridine (3) at T = 298 K.

1

2

3

343 344 345 346 347 H/mT

Table 1. EPR parameters of complexes 1—10 (hexane, 298 K)

Complex ai(1H) ai(

14N) ai(199Hg, 201Hg) g

mT

imSQHgPh (1) 0.23 0.51 1.30; 0.48 1.9964imSQHgEt (2) 0.25 0.52 0.68; 0.25 1.9969imSQHgPrn (3) 0.25 0.52 0.67; 0.25 1.9970imSQHgBu (4) 0.25 0.53 0.68; 0.25 1.9970imSQHgPri (5) 0.25 0.53 0.32; 0.12 1.9968imSQHgHexc (6) 0.26 0.54 0.32; 0.12 1.9968imSQHgCH2SiMe3 (7) 0.25 0.53 1.18; 0.44 1.9974imSQHg(p�FPh) (8) 0.25 0.51 1.42; 0.52 1.9964imSQHgFc (9) 0.24 0.51 1.72; 0.63 1.9971imSQHg� 0.24 0.52 1.42; 0.52 1.9970 (p�Me2NPh) (10)

Stable paramagnetic organomercury compounds Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013 149

an excess spin density in complexes 1—10 is concentratedat the oxygen atom, i.e., the o�iminobenzosemiquinoneligand shows the coordination mode similar to that of theamidophenoxy ligand.

The above�described structural features of the com�plexes were confirmed by X�ray diffraction data for com�pounds 3, 7, and 9. The molecular structures of the com�plexes are shown in Fig. 2. Selected bond lengths andbond angles in the complexes are given in Table 2.

According to the X�ray diffraction data, the coordina�tion units in complexes 1,19 3, 7, and 9 have similar struc�tures. The mercury atom in compounds 3, 7, and 9 is ina trigonal T�shaped environment and is located close to theplane formed by the O(1), N(1), and C(27) atoms (thedeviations from the plane are 0.018, 0.011, and 0.012 Å for3, 7, and 9, respectively; the corresponding value for 1 is0.071 Å19). The N(1)—Hg(1)—C(27) angle is close to 180and is in the range of 167.2(3)—174.05(15). The O(1)—C(2)bond lengths in compounds 1, 3, 7, and 9 are in the rangeof 1.261(4)—1.2681(19) Å and are slightly smaller thanthe corresponding lengths in most of the structurally cha�racterized metal complexes containing the monoreducedform of the o�iminobenzoquinone ligand.23 On the con�trary, the N(1)—C(1) bond length (1.337(9)—1.344(2) Å)is typical of metal o�iminosemiquinolate complexes.23 TheHg—N and Hg—O bond lengths are unusual for the radicalanion�type coordination of imQ. As a rule, the metal—oxy�gen and metal—nitrogen bond lengths in metal complexeswith o�iminosemiquinone radical anions are slightlylarger than the sums of the covalent radii of the cor�responding elements.21,23,24 In the mercury radicalcomplexes under consideration, the Hg(1)—N(1) bond(2.080(6)—2.1067(14) Å) is slightly shorter, whereas theHg(1)—O(1) bond (2.485(2)—2.500(5) Å) is substantiallylonger than the corresponding sum of the covalent radii ofthe elements (Hg—N, 2.11 Å; Hg—O, 2.10 Å).25 Thisindicates that the former bond is strong covalent, whereasthe latter bond is weak donor�acceptor.

These characteristics provide evidence that the coordi�nation of the radical ligand in the synthesized paramag�netic mercury(II) complexes is much more similar to theamidophenoxy�type mode than to the typical o�imino�semiquinone mode. The six�membered ring C(1)—C(6)displays an ortho�quinoid�type distortion characteristicof o�iminosemiquinones21,23,24 and it is manifested inthe alternation of the C—C bond lengths. Thus, theC(1)—C(2), C(1)—C(6), C(2)—C(3), and C(4)—C(5)distances are in the range of 1.417(11)—1.475(10) Å andthey are much longer than the C(3)—C(4) and C(5)—C(6)bonds (1.348(5)—1.375(2) Å). This patterns differs fromthe alternation of the bond lengths in phenoxyl radicals,where the short bonds are separated by two long bonds26

(the so�called para�quinoid�type distortion). Therefore,a weak coordination of the oxygen center to the mercuryatom in amidophenoxyl leads to a change in the type

of distortion of the radical ligand from para�quinoid toortho�quinoid.

A method was proposed23 for the analysis of the C—C,C—O, and C—N bond length distribution in metalo�iminoquinone complexes to estimate the formal oxida�

Fig. 2. Molecular structures of complexes 3 (a), 7 (b), and 9 (c).The thermal ellipsoids are drawn at the 50% probability level.Hydrogen atoms are omitted.

C(1)

C(2)

C(3)C(4)

C(5)

C(6)

O(1)

C(27)

N(1)

Hg(1)

C(1)

C(2)

C(3)

C(4)

C(5)

C(6)

O(1)Si(1)

N(1)

Hg(1)

C(1)

C(2)

C(3)

C(4)

C(5)

C(6)

O(1) Fe(1)

N(1)Hg(1)

a

b

C(27)

C(27)

c

Piskunov et al.150 Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013

tion state of the redox�active ligand. The formal oxidationstates of the o�iminosemiquinone ligands in complexes 1,3, 7, and 9 calculated according to this method are –0.61,–0.58, –0.69, and –0.44, respectively. It was noted23 thatsuch considerable deviations from an integer value arecharacteristic of complexes with a substantial degree of�donation from the ligand to the metal. This intramole�cular donor�acceptor interaction can account for theT�shaped coordination environment of the mercury atom.The fact that the N(1)—Hg(1)—C(27) angle is close to180 attests to the nearly sp hybridization of the metalorbitals. Due to two sp�hybridized orbitals, the mercuryatom forms two covalent bonds with the nitrogen atom ofthe redox�active ligand and the carbon atom of the alkyl(aryl) substituent. This hybridization state can be stabi�lized by an additional interaction between the free unhy�bridized p orbital of the metal atom and the �system ofthe o�iminoquinone ligand. Another orthogonal unhybrid�ized p orbital is involved in the coordination bonding ofthe phenoxyl oxygen atom.

As can be seen from Table 1, the hyperfine couplingconstant of the magnetic mercury isotopes in the EPRspectra is very sensitive to the nature of the hydrocarbonsubstituent at the metal atom. Its value increases by al�most a factor of three in going from the isopropyl substitu�ent to the ferrocenyl substituent (from 0.67 (R = Pri) to1.72 mT (R = Fc) in hexane). The proton and nitrogenhyperfine coupling constants remain unchanged withinexperimental error. An analysis of the structural parame�ters for complexes 1, 3, 7, and 9 shows that the increase in

the hyperfine coupling constant ai(199Hg) in the series

3 < 7 < 1 < 9 is accompanied by a shortening of theN(1)—Hg(1) and C(27)—Hg(1) bonds. It should be notedthat the changes in the EPR parameters do not correlatewith the changes in the O(1)—Hg(1) distance or theN(1)—Hg(1)—C(27) angle. The spin density from the ra�dical ligand can be delocalized on the mercury atom throughtwo channels: via the direct involvement of the vacantp�orbital of mercury in the molecular orbital of the ligandoccupied by an unpaired electron and via the spin polar�ization of the atomic orbitals of mercury involved in theHg—N and Hg—O bond formation. It is difficult to esti�mate the contribution of each particular channel withoutperforming special calculations. However, it is evident thata shortening of the mercury—nitrogen bond will facilitatean increase in the degree of spin density transfer to themetal atom through both mechanisms.

It was shown19 that the EPR parameters for solutionsof complex 1 substantially depend on the nature of thesolvent. The largest changes are observed for the hyperfinecoupling constants of the magnetic mercury isotopes. Thesimilar tendency was found in all complexes 2—10 (seeFig. 1). In the present study, we performed additionalinvestigations of the solvent effect on the EPR parametersof complexes 1—10. The results of these investigations arepresented in Table 3.

Regardless of the nature of the substituent R in com�plexes 1—10, the smallest hyperfine coupling constantai(

199Hg) is observed in hexane and the largest one is ob�served in pyridine. An analysis of the EPR parameters for1—10 in relation to the changes in different properties ofthe solvents (the donor number, the acceptor number, andthe polarity) showed that the best correlation is observedin the ai(

199Hg) — ET coordinates, where ET is the empir�ical polarity parameter27 (Fig. 3). The correlation coeffi�

Table 2. Selected bond lengths and bond angles in complexes 1,3, 7, and 9

Parameter 1 3 7 9

Bond d/Å

Hg(1)—O(1) 2.452(3) 2.4927(13) 2.485(2) 2.500(5) Hg(1)—N(1) 2.082(3) 2.1067(14) 2.093(3) 2.080(6) Hg(1)—C(27) 2.042(4) 2.076(2) 2.068(5) 2.028(8) N(1)—C(1) 1.346(4) 1.344(2) 1.342(4) 1.337(9) O(1)—C(2) 1.261(4) 1.2681(19) 1.266(5) 1.264(9) C(1)—C(2) 1.465(5) 1.475(2) 1.461(6) 1.475(10) C(2)—C(3) 1.445(5) 1.451(2) 1.447(5) 1.462(11) C(3)—C(4) 1.355(5) 1.373(2) 1.373(6) 1.368(11) C(4)—C(5) 1.421(5) 1.431(2) 1.437(6) 1.462(11) C(5)—C(6) 1.363(5) 1.375(2) 1.348(5) 1.367(12) C(1)—C(6) 1.410(5) 1.419(2) 1.423(6) 1.417(11)

Angle /deg

O(1)—Hg(1)— 172.32(10) 171.49(5) 171.38(10) 171.7(2) —N(1) O(1)—Hg(1)— 116.77(13) 116.96(7) 114.53(14) 121.0(3) —C(27) N(1)—Hg(1)— 169.95(14) 171.39(7) 174.05(15) 167.2(3) —C(27)

Fig. 3. Effect of the polarity of the solvent on the hyperfinecoupling constant ai(

199Hg) for complexes 1, 3, 5, 7, 9, and 10.Solvents: 1, hexane; 2, triethylamine; 3, toluene; 4, diethyl ether;5, 1,4�dioxane; 6, THF; 7, ethyl acetate; 8, CH2Cl2; 9, aceto�nitrile; 10, pyridine.

0.5

0.4

0.3

0.2

0.1

9 9 9 9

10 8 1010

88

6 7

6

7

676 6

4

3

1

54

32

43

43

43

1 12

121

4

3

1

0.7 1.2 1.7 ai(199Hg))/ mT

ET

1357910

10 10 10

Stable paramagnetic organomercury compounds Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013 151

cients are in the range of 0.77—0.97 (the constantsai(

199Hg) in pyridine are not included in the correlation).The hyperfine coupling constant of the magnetic mercuryisotopes increases with increasing polarity of the solvent.

It is noteworthy that the hyperfine coupling constantsfound in pyridine do not fit the nearly linear ai(

199Hg) — ETplots. This indicates that the polarity of the solvent is notthe only parameter that has an effect on the spectroscopiccharacteristics of the resulting radical complexes. Takinginto account that pyridine is a strongly coordinating sol�vent capable of forming strong donor�acceptor bonds with

metal cations, the solvation mechanism of the solvent ef�fect on the constant ai(

199Hg), which has been describedearlier for o�semiquinone and o�iminosemiquinone deri�vatives of thallium(I)6,28 and lead(II),8 cannot be ruled outas well. The solvation mechanism is additionally confirmedby the temperature dependence of the EPR spectra of com�plexes 1—10 (Figs 4—6).

As the temperature decreases, the equilibrium shifts tothe right (Scheme 2), resulting in an increase in the hyper�fine coupling constant of the magnetic metal isotopes.6,8,28

An increase in the donor number of the solvent27 shouldlead to an increase in the heat of solvation, which deter�mines the sensitivity of the equilibrium reaction (seeScheme 2) to changes in the temperature. Actually, thechange in the donor properties of the solvent affects theslope of the linear dependence ai(

199Hg)—f(T) (see Fig. 6).The latter is more than two times larger in pyridine thanin hexane.

In the series of compounds 1—10, complex 9 contain�ing two redox�active centers, viz., the o�iminosemiquino�

Table 3. Hyperfine coupling constants ai(199Hg) (mT) for complexes 1—10 in different solvents at 298 K

Complex Hexane NEt3 Toluene Et2O 1,4�Dioxane THF Ethyl acetate CH2Cl2 MeCN Py

1 1.30 1.38 1.44 1.42 — 1.60 1.57 1.60 1.80 2.082 0.68 — 0.72 0.71 — 0.83 0.82 — — 1.083 0.67 0.72 0.76 0.72 0.84 0.86 0.83 0.86 0.94 1.074 0.68 — 0.75 0.72 — 0.83 — — 0.92 1.075 0.32 — 0.36 0.34 — 0.45 — — — 0.76 0.32 — 0.35 0.32 — 0.47 — — — 0.687 1.18 — 1.18 1.22 — 1.34 1.32 — 1.37 1.548 1.42 1.55 1.53 1.52 — 1.78 1.72 — — 2.289 1.72 — 1.86 1.83 — 1.96 — — — 2.3410 1.42 1.42 1.50 1.46 — 1.58 1.56 1.66 1.76 2.00

Fig. 4. Isotropic EPR spectrum of complex 7 in THF at 300 (1),260 (2), and 220 K (3).

1

2

3

336 337 338 339 340 H/mT Fig. 5. Effect of the temperature on the hyperfine coupling con�stant ai(

199Hg) for complexes 1 (3), 3 (5), 6 (6), 8 (2), 7 (4), and10 (1) in THF.

2.2

1.9

1.6

1.3

1.0

0.7

ai(199Hg)/mT

1

2

3

4

5

6

220 240 260 280 300 T/K

Piskunov et al.152 Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013

late ligand and the ferrocenyl substituent, is of particularinterest. Hence, the redox properties of complex 9 werestudied by cyclic voltammetry (CV). According to the CVdata, compound 9 undergoes three reversible one�electronredox steps in the potential range under study (Fig. 7).

The reversible reduction of the o�iminobenzosemi�quinone ligand is observed during a cathodic potentialscan at ERed

1/2 = –0.55 V. The oxidation of complex 9involves two consecutive one�electron steps (ЕOx1

1/2 == 0.27 V; ЕOx2

1/2 = 0.48 V). In the potential range underconsideration, both the ferrocenyl and o�iminobenzosemi�quinone moieties can be equally involved in electroche�mical transformations. To reveal the sequence of redox trans�formations, we performed the electrolysis of complex 9 forthree hours at a controlled potential of 0.39 V. In the rangefrom 650 to 900 nm, the absorption spectrum of the start�ing compound 9 shows a broad band corresponding to thecharge transfer in the imSQ moiety. Similar low�intensityabsorption bands have been observed earlier and are cha�racteristic of metal o�iminosemiquinolate complexes.29 Theelectrolysis is accompanied by the disappearance of theabsorption band in the long�wavelength region of the spec�

trum and the appearance of a new band with a maximumat 393 nm characteristic of free o�iminobenzoquinone.30

The changes in the electronic absorption spectrumare consistent with the results of the electrochemicalexperiment. Thus, the first redox transition is absent inthe cyclic voltammetry curve, and the potential of thesecond anodic step shifts to 0.39 V. The cathodicbranch shows the reduction peak of the o�iminobenzo�quinone ligand at –0.78 V.31 These data suggest the mech�anism of redox transformations of complex 9 presented inScheme 3.

The monocationic complex generated during the elec�trolysis at a controlled potential is unstable and under�goes decomposition accompanied by the release of freeo�iminobenzoquinone from the coordination sphere.The formation of the latter is evidenced by the electro�chemical and spectroscopic data. Consequently, ofthe two potential redox centers in complex 9, the o�imino�semiquinone ligand is involved in the first electrochemi�cal step followed by the oxidation of the ferrocenylmoiety.aaa

To summarize, we synthesized for the first time a seriesof stable organomercury compounds based on the o�imino�semiquinone ligand. In these derivatives, the amido�phenoxy�type coordination mode of the radical ligandprevails. It was shown that the hyperfine coupling con�stant of the magnetic mercury isotopes in the paramag�netic complexes depends not only on the nature of thehydrocarbon substituent at the metal atom but also on theproperties of the solvent, in which the EPR spectrum isrecorded. Not only the increase in the polarity of the me�dium but also the ability of the solvent molecules to beinvolved in specific solvation cause an increase in the con�stant ai(

199,201Hg).

Fig. 6. Effect of the temperature on the hyperfine coupling con�stant ai(

199Hg) for complex 1 in hexane (1), toluene (2), ethylacetate (3), THF (4), and pyridine (5).

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

ai(199Hg)/mT

1

2

3

4

5

220 240 260 280 300 320 T/K

Scheme 2

Fig. 7. Cyclic voltammetry for complex 9: the solid line indicatesthe starting complex; the dashed line indicates the electrolysisproduct at +0.39 V (CH2Cl2—CH3CN, 1 : 1); V = 0.2 V s–1,Ag/AgCl/KCl, C = 2•10–3 mol L–1, glassy carbon electrode, Ar,0.1 M Bu4NClO4.

0.04

0.03

0.02

0.01

0

–0.01

–0.02

I/mA

–0.6 –0.4 –0.2 0 0.2 0.4 0.6 0.8 E/V

Stable paramagnetic organomercury compounds Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013 153

Experimental

Experiments on the synthesis and investigations of mer�cury(II) o�iminobenzosemiquinolate complexes were carried outunder reduced pressure in the absence of traces of oxygenand water.

The IR spectra were recorded on a FSM�1201 Fourier trans�form infrared spectrometer in Nujol in KBr cells. The electronicabsorption spectra were measured on a Perkin�Elmer Lambda25 spectrometer. The EPR spectra were recorded on a Bru�ker EMX spectrometer using 2,2�diphenyl�1�picrylhydrazyl(g = 2.0037) as the reference for the determination of the g factor.The precise parameters were determined by simulating the EPRspectra with the use of the Bruker WinEPR SimFonia software.The oxidation potentials were measured under an argon atmo�sphere by cyclic voltammetry in a three�electrode electroche�mical cell using an IPC�pro potentiostat. A stationary glassy carbonelectrode (d = 2 mm) was used as the working electrode, a plati�num plate (S = 18 mm2) served as the auxiliary electrode, anda silver chloride electrode (Ag/AgCl/KCl) with a water�imper�meable membrane was used as the reference electrode. The po�tential scan rate was 0.2 V s–1; 0.1 M Bu4NClO4 (99%, Acros),which was twice recrystallized from aqueous EtOH and driedin vacuo at 50 C for 48 h, served as the supporting electro�lyte. The microelectrolysis of complex 9 was performed usinga PI�50�1.1 potentiostat and stationary platinum electrodes(S = 30 mm2) in an undivided three�electrode cell (V = 2 mL) ata potential of 0.39 V. The electrolysis time was 3 h. The conver�sion of complex 9 was 98 %. An (Ag/AgCl/KCl) electrode withan electroconductive water�impermeable membrane was usedas the reference electrode.

The solvents were purified and dehydrated accordingto recommendations.32 Organomercury compounds RHgCl

(R = Et, Prn, Bun, Pri, Hexc, CH2SiMe3, Ph, p�F�Ph, Fc),33

RHgOAc (p�Me2N�Ph),33 and sodium o�iminobenzosemiquino�late imSQNa21 were synthesized according to known procedures.The compound imSQNa was used in the in situ synthesis. Thecomplex imSQHgPh (1) was synthesized according to a proce�dure described earlier.19

Synthesis of complexes 2—10 (general procedure). A solutionof sodium o�iminobenzosemiquinolate (0.8 mmol) in THF(20 mL) was slowly added to a solution of the organomercurycompound RHgCl (0.8 mmol) in the same solvent (10 mL),which was accompanied by a change in the color of the reactionmixture from bright�blue to emerald�green (in the case of com�plex 10, to violet). Then the solution was kept at ~20 C for20 min, the solvent was removed under reduced pressure, the dryresidue was treated with hexane (25 mL), and a precipitate ofNaCl or NaOAc was filtered off on a Schott glass filter (porosity 4).Hexane was removed under reduced pressure, and the residuewas dissolved in ethanol. The solution was kept at –18 C over�night. Crystals of mercury o�iminobenzosemiquinolate complex�es were separated from the mother liquor by decantation anddried under reduced pressure. Complex 10 was crystallized fromhexane at –18 C. In the case of compound 9, the dry residueobtained after the removal of hexane was dissolved in pentane.Then the solvent was kept at –18 C to obtain a crystallineproduct.

In the crystalline state, all mercury(II) o�iminobenzosemi�quinolate complexes are stable to atmospheric moisture and ox�ygen. Solid samples decompose without melting upon heatingabove 130 C. The compounds are readily soluble in most oforganic solvents.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]ethylmercury(II) (2). Yield 0.360 g (74 %). Found (%):C, 55.36; H, 7.07; Hg, 32.84. C28H42HgNO. Calculated (%):C, 55.20; H, 6.95; Hg, 32.93. IR, /cm–1: 1585 s, 1527 s, 1499 m,

Scheme 3

Piskunov et al.154 Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013

Table 4. Crystallographic characteristics and the X�ray data collection and structure refinement statistics forcomplexes 3, 7, and 9

Parameter 3 7 9

Molecular formula C29H44HgNO C30H48HgNOSi C36H46FeHgNOMolecular weight 623.24 667.37 765.18Temperature/K 100(2) 100(2) 150(2)Crystal system Monoclinic Monoclinic Monoclinic Space group P2(1)/n C2/c P2(1)/ca/Å 13.5652(3) 25.758(3) 20.023(3)b/Å 12.7584(2) 14.8399(14) 14.710(3)c/Å 17.5357(3) 20.801(2) 11.2383(19)/deg 90 90 90/deg 112.7028(19) 128.0320(10) 101.557(4)/deg 90 90 90V/Å 2799.77(9) 6262.9(10) 3243.0(10)Z 4 8 4calc/g cm–3 1.479 1.416 1.567/mm–1 5.517 4.974 5.203F(000) 1252 2696 1532Crystal dimension/mm 0.20×0.10×0.10 0.20×0.08×0.05 0.14×0.13×0.05�Scan range/deg 3.19—30.00 2.02—26.00 1.73—26.00hkl ranges –19 h 19 –31 h 31 –24 h 22

–17 k 17 –18 k 18 –18 k 17–24 l 24 –25 l 25 –8 l 13

Number of reflections 54185 26530 18598Number of unique reflections 8119 6158 6345Rint 0.0375 0.0815 0.0872GOOF (F2) 1.046 0.990 1.042R1/wR2 (I > 2(I)) 0.0213/0.0481 0.0417/0.0798 0.0603/0.1265R1/wR2 (based on all reflections) 0.0287/0.0504 0.0753/0.0872 0.1092/0.1395Residual electron density density max/min/e Å–3 1.261/–1.068 1.760/–0.638 3.842/–1.766

1481 s, 1452 s, 1440 s, 1357 s, 1339 s, 1336 m, 1320 m, 1302 m,1267 w, 1253 s, 1196 s, 1181 m, 1165 s, 1113 m, 1100 m, 1080 w,1055 m, 1042 m, 1028 m, 991 m, 967 w, 935 w, 912 m, 888 w,876 m, 857 m, 825 w, 797 s, 784 w, 765 m, 742 w, 708 w, 685 w,659 w, 648 w, 627 w, 601 w, 580 w, 567 w, 538 w, 529 w, 523 w,495 w, 469 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]�n�propylmercury(II) (3). Yield 0.410 g (82.5%).Found (%): C, 55.96; H, 7.21; Hg, 32.09. C29H44HgNO. Calcu�lated (%): C, 55.89; H, 7.12; Hg, 32.18. IR, /cm–1: 1586 s, 1530m, 1524 s, 1500 m, 1483 s, 1452 s, 1438 s, 1418 m, 1363 s, 1354 s,1338 m, 1331 m, 1317 m, 1297 w, 1275 w, 1269 w, 1252 s, 1207 w,1198 m, 1181 m, 1162 m, 1111 m, 1097 w, 1051 m, 1040 w, 1025 m,1004 w, 990 m, 966 w, 934 w, 909 m, 882 w, 874 w, 854 m, 825 w,796 s, 784 w, 765 w, 730 w, 707 w, 659 w, 650 w, 626 w, 603 w,581 w, 570 w, 540 w, 528 w, 495 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]�n�butylmercury(II) (4). Yield 0.403 g (79.1%).Found (%): C, 56.66; H, 7.31; Hg, 32.42. C30H46HgNO. Calcu�lated (%): C, 56.54; H, 7.28; Hg, 32.48. IR, /cm–1: 1587 s, 1531 m,1526 m, 1503 m, 1482 s, 1453 s, 1438 s, 1381 s, 1360 s, 1356 s,1340 m, 1320 m, 1311 m, 1304 m, 1293 w, 1266 w, 1252 s, 1207 w,1198 m, 1189 w, 1179 m, 1163 m, 1113 m, 1107 w, 1097 w,1053 w, 1039 w, 1026 m, 991 m, 972 w, 950 w, 934 w, 911 m,

887 w, 878 m, 854 m, 825 w, 798 s, 784 w, 765 m, 743 w, 710 w,687 w, 658 w, 650 w, 628 w, 602 w, 580 w, 569 w, 539 w, 529 w,494 w, 466 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]isopropylmercury(II) (5). Yield 0.364 g (73%).Found (%): C, 55.94; H, 7.19; Hg, 32.10. C29H44HgNO. Calcu�lated (%): C, 55.89; H, 7.12; Hg, 32.18. IR, /cm–1: 1583 s, 1524 m,1501 m, 1483 s, 1451 s, 1438 s, 1360 s, 1354 s, 1337 m, 1320 m,1304 m, 1265 w, 1252 s, 1198 s, 1179 w, 1165 m, 1153 m, 1111 m,1099 m, 1055 m, 1042 w, 1026 m, 1007 w, 990 m, 934 w, 911 m,887 w, 878 w, 855 m, 799 s, 784 w, 765 m, 742 w, 658 w, 649 w,628 w, 601 w, 577 w, 568 w, 538 w, 529 w, 495 w, 466 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]�c�hexylmercury(II) (6). Yield 0.426 g (80.2%).Found (%): C, 58.04; H, 7.33; Hg, 30.19. C32H48HgNO. Calcu�lated (%): C, 57.94; H, 7.29; Hg, 30.24. IR, /cm–1: 1584 s, 1529 s,1524 s, 1503 m, 1482 s, 1453 s, 1437 s, 1382 s, 1360 s, 1354 s,1338 m, 1321 m, 1310 m, 1300 m, 1265 m, 1253 s, 1209 w, 1198 m,1174 m, 1165 s, 1110 m, 1098 m, 1082 m, 1051 m, 1039 m,1024 m, 991 s, 934 w, 933 m, 912 m, 898 w, 887 m, 876 m, 855 m,840 w, 823 w, 797 s, 785 m, 764 m, 742 w, 670 w, 660 w, 651 w,625 m, 603 w, 581 w, 569 w, 539 w, 529 w, 495 w, 466 w, 460 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato](trimethylsilylmethyl)mercury(II) (7). Yield 0.369 g

Stable paramagnetic organomercury compounds Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013 155

(69.1%). Found (%): C, 54.06; H, 7.30; Hg, 30.01; Si, 4.17.C30H48HgNOSi. Calculated (%): C, 53.99; H, 7.25; Hg, 30.06;Si, 4.21. IR, /cm–1: 1584 s, 1530 m, 1524 s, 1500 m, 1483 s,1454 s, 1447 s, 1434 s, 1410 m, 1357 s, 1340 m, 1320 m, 1303 m,1261 m, 1250 s, 1211 w, 1200 m, 1177 w, 1166 m, 1112 m, 1097 m,1080 m, 1054 m, 1038 m, 1027 m, 1007 m, 993 m, 963 w, 933 w,914 m, 887 w, 878 m, 853 s, 834 s, 802 m, 785 w, 770 m, 754 w,744 w, 712 m, 694 w, 658 w, 649 w, 630 w, 613 w, 601 w, 579 w,568 w, 546 w, 537 w, 531 w, 523 w, 496 w, 470 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato](p�fluorophenyl)mercury(II) (8). Yield 0.414 g(76.7%). Found (%): C, 56.98; H, 6.21; Hg, 29.67; F, 2.74.C32H41FHgNO. Calculated (%): C, 56.92; H, 6.12; Hg, 29.71;F, 2.81. IR, /cm–1: 1583 s, 1531 m, 1523 m, 1504 m, 1488 s,1480 s, 1452 s, 1443 s, 1418 w, 1384 m, 1362 m, 1356 s, 1337 m,1321 m, 1310 w, 1305 m, 1254 m, 1228 m, 1217 s, 1198 m, 1179 w,1167 s, 1110 m, 1098 m, 1088 w, 1053 m, 1037 w, 1026 m,1021 m, 992 m, 936 w, 912 m, 887 w, 880 m, 856 m, 825 m, 816 s,800 s, 786 m, 765 m, 758 w, 743 w, 705 w, 689 w, 659 w, 650 w, 630 w,603 w, 579 w, 571 w, 541 w, 529 w, 507 m, 496 w, 469 w, 461 w.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato]ferrocenylmercury(II) (9). Yield 0.417 g (68.1%).Found (%): C, 56.58; H, 6.11; Hg, 26.12; Fe, 7.24.C36H46FeHgNO. Calculated (%): C, 56.51; H, 6.06; Hg, 26.21;Fe, 7.30. IR, /cm–1: 1586 s, 1529 m, 1523 m, 1478 s, 1447 s,1413 m, 1356 m, 1339 m, 1320 m, 1302 m, 1253 m, 1197 m, 1180 m,1163 m, 1143 m, 1114 w, 1105 m, 1055 m, 1022 m, 1000 m, 992 m,972 w, 935 w, 929 w, 911 m, 876 m, 859 m, 825 m, 811 m, 799 m,785 m, 764 w, 659 w, 648 w, 630 w, 604 w, 566 w, 488 m, 480 m.

[4,6�Di�tert�butyl�N�(2,6�diisopropylphenyl)�o�iminobenzo�semiquinolato](p�N,N�dimethylaminophenyl)mercury(II) (10).Yield 0.412 g (73.6%). Found (%): C, 58.48; H, 6.81; Hg, 28.58.C34H47HgN2O. Calculated (%): C, 58.31; H, 6.76; Hg, 28.64.IR, /cm–1: 1592 s, 1546 w, 1525 w, 1505 s, 1480 s, 1455 s, 1449 s,1357 s, 1344 m, 1322 m, 1285 w, 1253 m, 1233 m, 1202 m, 1165 m,1113 w, 1098 w, 1087 m, 1058 m, 1043 w, 992 m, 948 w, 934 w,910 m, 878 w, 857 m, 801 s, 784 w, 766 w, 754 w, 704 w, 658 w,648 w, 630 w, 603 w, 567 w, 538 w, 526 w, 521 w, 514 w, 495 w.

X�ray diffraction study. Crystals suitable for X�ray diffractionstudy were obtained by crystallization from ethanol (for com�pounds 3 and 7) or from pentane (for compound 9). The X�raydiffraction data sets for complexes 3, 7, and 9 were collected ona Smart Apex diffractometer (Mo�K radiation, graphite mono�chromator). The structures were solved by direct methods andrefined by the full�matrix least�squares method based on F 2 withthe use of the SHELXTL program package.34 The absorptioncorrection was applied using the SADABS program.35 The non�hydrogen atoms were refined with anisotropic displacement para�meters. The hydrogen atoms were positioned geometrically andrefined using a riding model. Selected bond lengths and bondangles in molecules 3, 7, and 9 are listed in Table 2. Crystallo�graphic characteristics and the X�ray data collection and struc�ture refinement statistics are given in Table 4.

The crystallographic data for complexes 3 (CCDC 910782),7 (CCDC 910781), and 9 (CCDC 910780) were deposited withthe Cambridge Crystallographic Data Centre (Cambridge Crys�tallographic Date Centre).*

This study was financially supported by the RussianFoundation for Basic Research (Project Nos 13�03�01022�a, 12�03�31026, and 11�03�00389) and the Council onGrants at the President of the Russian Federation (Pro�gram for State Support of Leading Scientific Schools ofthe Russian Federation, Grant NSh�1113.2012.3).

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