V. K. Cherkasov

ESR investigation of copper(I) complexes with o-semiquinolate ligands

Abstract Solutions of o -semiquinolatecopper(I) complexes with neutral ligands, such as PPh 3 , P(OEt) 3 , AsPh 3 , AsEt 3 , cyclooctadiene-1,5, PhCCPh, PhCCH and CO, were investigated by ESR. The spectra of the complexes are characterised by high specificity and sensitivity to configuration of ligand surroundings. The radical character of the o -semiquinolate ligand remains constant over the chemical transformation in the metal coordination sphere. These properties allow the use of o -semiquinolate ligands as a special “spin mark” in the chemistry of coordination compounds.

An EPR investigation of the thermodynamics and kinetics of a reversible intramolecular metal-ligand electron transfer in rhodium complexes

Abstract The temperature dependence of a reversible intramolecular metal-ligand electron transfer for a series of semiquinone-rhodium(I) complexes in equilibrium with their catecholate-rhodium(II) isomers has been investigated by EPR spectroscopy, in a wide range of solvents. Both the thermodynamics and kinetics of this process are reported, along with a discussion of the role of the solvent and of the electronic and molecular structure of the complexes.

ESR investigation of the substitution reactions in rhodium(I) complexes with spin-labeled ligands

Abstract A number of new spin-labelled Rh I complexes containing both the 3,6-ditert-butyl- o -benzosemiquinone (3,6-SQ) fragment and n- and π-donor ligands have been prepared. The tetracoordinate derivatives of the composition L 2 Rh-(3,6-SQ), where L  CO, P(OPh) 3 , L  1/2 1,5-COD and the pentacoordinate complex (PPh 3 ) 2 Rh(3,6-SQ)(CO) were isolated in individual state, the formation of other rhodium compounds was registered by ESR spectroscopy. The presence of an o -benzosemiquinolate ligand in the molecule with the unpaired electron located essentially on this fragment does not significantly influence on the reactivity of the metal ion in most cases; the n- and π-donor ligands exchange reactions studied by ESR confirm this fact. (PPh 3 ) 2 Rh(3,6-SQ) has an abnormal distribution of spin density of the unpaired electron in the molecule, mostly located on the metal atom, this derivative bearing a close analogy to the rhodium(II) ( d 7 ) complexes.

Reaction on the addition of some organometallic compounds to 3,6-di-tert-butyl-o-benzoquinone: new o-quinones

Abstract 3,6-Di- tert -butyl- o -benzosemiquinone is very convenient for the investigation of the interaction between organometallic R 2 M and carbonyl compounds. The reaction of organometallic compounds R 2 M with o-quinone, where R = Ph, Me, Et, Pr, 1 Pr or t Bu and M ≡ Zn, Cd, and Al, proceeds in two ways: (1) the single-electron oxidation of the organometallic compound by o -quinone, resulting in derivatives of alkyl(phenyl)oxyphenols; (2) the polar 1,2 and 1,4 addition of organometallic molecules to o -quinone as to conjugated ketone, which produces hydroxycyclohexadienones after hydrolysis. The relationship between these two is defined by the nature of the organometallic compound. The products of polar addition are rearranged easily in different ways, finally resulting in new o-quinones: 3-(R)-6- tert -butyl- o -benzoquinones and 3,6-di- tert -butyl-4-(R)- o -benzoquinones where R ≡ alkyl.

Oxidation by oxygen and sulfur of Tin(IV) derivatives containing a redox-active o-amidophenolate ligand.

Oxidation of tin(IV) o-amidophenolate complexes [Sn(ap)Ph(2)] (1) and [Sn(ap)Et(2)(thf)] (2) (ap=dianion of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (ImQ)) with molecular oxygen and sulfur in toluene solutions was investigated. The reaction of oxygen with 1 at room temperature forms a paramagnetic derivative [Sn(isq)(2)Ph(2)] (3) (isq=radical anion of ImQ) and diphenyltin(IV) oxide [{Ph(2)SnO}(n)]. Interaction of 1 with sulfur gives another monophenyl-substituted paramagnetic tin(IV) complex, [Sn(ap)(isq)Ph] (4), and the sulfide, [Ph(3)Sn](2)S. The oxidation of 2 with oxygen and with sulfur proceeds through the derivative [Sn(isq)(2)Et(2)] (7), which undergoes alkyl elimination to give two new tin(IV) compounds, [Sn(ap)(isq)Et] (5) and [Sn(ap)(EtImQ)Et] (6) (EtImQ=2,4-di-tert-butyl-6-(2,6-diisopropylphenylimino)-3-ethylcyclohexa-1,4-dienolate ligand), respectively, along with the corresponding alkyltin(IV) oxide and sulfide. Complexes 3-5 and 7 were studied by EPR spectroscopy. The structures of 3, 4 and 6 were investigated by X-ray analysis.

SYNTHESIS AND ESR-CHARACTERIZATION OF RADICAL ANION COMPLEXES OF LANTHANUM. X-RAY CRYSTAL STRUCTURE OF THE MIXED BIPY, BIPY-1 COMPLEX OF LANTHANUM(III ) LAI2(BIPY)(BIPY)(DME) : EVIDENCE FOR AN INTER-LIGAND CHARGE TRANSFER

Abstract The reaction of [LaI2(THF)3]2[C10H8] with excess of 2,2′-bipyridine (bipy) in DME or THF results in the formation of mixed radical anion ligand/neutral ligand complexes [LaI2(bipy(0))(bipy(−1))(L)n (DME)(1) and (THF)2 (2), whereas a reactant reactant ratio of 1:2 generates the mono-bipy complex [LaI2(bipy)(DME)2] (3). ESR and IR spectroscopic data show a fast shuttle electron transfer (SIET) between the neutral and the radical anion of bipy in1 and2. The X-ray structure shows1 to be monoclinic, space group P2/c, Z = 2, with a = 10.0320(12), b = 9.7510(11), c = 16.296(8)A˚, β = 90.43(2)°. The structure was refined toR = 0.0360 for 2562 observed reflections (1 > 2σ(1)). It shows the lanthanum atom eight-coordinated by two iodine, two oxygen and four nitrogen atoms.

o-Semiquinolate complexes of manganese and rhenium formed by interaction of decacarbonyls of these elements with hindered o-quinones

Abstract The influence of different solvents (oxygen-, sulfur-, and nitrogen-containing solvents, alkanes and aromatic hydrocarbons) and some donor ligands (triphenylphosphine, triphenylphosphite, cyclohexyl-isocyanide, triethylamine, cyclooctadiene) on ESR spectral parameters of manganese and rhenium o -semi-quinolate complexes formed in the reactions of Mn 2 (CO) 10 and Re 2 (CO) 10 with hindered o -quinones (3,5- and 3,6-di-tert-butylbenzoquinones-1,2, perchloroxantrenquinone-2,3, tetrachlorobenzoquinone-1,2) have been investigated by the ESR method.

The synthesis and properties of o-semiquinolate copper complexes

Abstract New neutral bis- o -semiquinolate copper(II) complexes with benzosemiquinone-1,2; 3,5- and 3,6-di-tert-butylbenzosemiquinone-1,2 and perchloroxanthrensemiquinone-1,2 were synthesised. The results of physical measurements showed that these complexes were the copper(II) ones with two paramagnetic ligands. Besides chemical properties of these complexes, we also studied, in particular, redox reactions, thermal decomposition, interaction with n- and π-donor compounds, etc. A useful method of synthesis of spin-marked copper(I) complexes by reaction of bis-3,5-di-tert-butylbenzosemiquinolate copper(II) complexes with n- and π-donor ligands is proposed. This method is illustrated by the preparation of new bis-(tert-butylisocyanide)-3,5-di-tert-butylbenzosemiquinolate-1,2 complexes.

Functionalization of sterically hindered o-benzoquinones: amino-substituted 3,6-di(tert-butyl)-o-benzoquinones

New sterically hindered functionalized o-quinones were synthesized by the 1,4-nucleophilic addition of secondary cyclic amines to 3,6-di(tert-butyl)-o-benzoquinone. The ability of these o-quinones to form o-semiquinone complexes with transition and main-group metals was studied by ESR spectroscopy in solution.

Reduction of vanadium(II) to vanadium(O) by naphthaleneytterbium: synthesis and X-ray crystal structure of the two-dimensional multidecker complex [(η5-C5H5)V(μ-η6:η2-C10H8)Yb(THF)-(η5-C5H5)]n

Abstract The reaction of (C 5 H 5 ) 2 V with an excess of (C 10 H 8 )Yb(THF) 2 in tetrahydrofuran at room temperature generated the polymeric two-dimensional multidecker complex [(η 5 -C 5 H 5 )V(μ-η 6 :η 2 -C 10 H 8 )Yb(THF)(η 5 -C 5 H 5 )] n , ( 1 ), which is also obtained from the reaction of YbI 2 (THF) 2 with an equimolar mixture of KC 5 H 5 and K[(C 5 H 5 )V(C 10 H 8 )] in tetrahydrofuran. The new compound was characterized by elemental analyses, magnetic susceptibility, IR and ESR spectra. The X-ray structural analysis of 1 showed the compound to be monoclinic, space group C2/c , Z =8, with a =19.07(5), b =13.61(3), c =17.40(3) A, β=91.9(2)° and D calc =1.84 g cm −3 . The structure was solved from 2482 observed reflections with F o > 4σ(F o ) and refined to a final R value of 0.047. The molecular structure consists of infinite zig-zag chains formed by (η 5 -C 5 H 5 )Yb moieties and with one (η 5 -C 5 H 5 )V(η 6 -C 10 H 8 ) unit coordinated η 2 via the naphthalene to each Yb atom.