Bis(1,4-di-tert-butyl-1,4-diazabutadiene)copper(i) [(3,6-di-tert-butyl-o-benzosemiquinono)(3,6-di-tert-butyl-catecholato)cuprate(ii)]. The molecular structure and intramolecular electron transfer

Bis(1,4-di-tert-butyl-1,4-diazabutadiene)copper(i) [(3,6-di-tert-butyl-o-benzosemiquinono)(3,6-di-tert-butylcatecholato)cuprate(ii)] (1) was synthesized. Complex 1 contains the 1,4-di-tert-butyl-1,4-diazabutadiene and 3,6-di-tert-butyl-o-benzoquinone ligands in the reduced form. The structure of 1 was established by X-ray diffraction analysis. The ESR spectra indicate that dissolution of complex 1 in organic solvents (toluene, THF, CH₂Cl₂, etc.) leads to its symmetrization to give neutral complex 2, which occurs in solutions as an equilibrium mixture of two redox isomers, viz., catecholate (Cat) complex 2c and semiquinone (SQ) complex 2s. In the coordination sphere of the copper atom, the reversible intramolecular metal—ligand electron transfer can proceed as successive steps as exemplified by the reactions of 2 with CO and 2,6-dimethylphenylisonitrile. Copper(i) o-semiquinone complex 2s can be reversibly transformed into copper(ii) catecholate complex 2c through electron transfer from the copper(i) atom to the SQ ligand. The subsequent addition of the neutral ligand (CO or CNAr) to 2c induces, in turn, electron transfer from the Cat ligand to the copper(ii) atom accompanied by the transformation of the catecholate complex into the o-semiquinone complex. In the case of CO, this transformation is also reversible and is efficiently controlled by the temperature.     

Ligand effects on the ferro- to antiferromagnetic exchange ratio in bis(o-semiquinonato)copper(II)

Heterospin complexes [Cu(SQ)2Py].C7H8, Cu(SQ)2DABCO, and [Cu(SQ)2NIT-mPy].C6H6, where Cu(SQ)2 is bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper(II), DABCO is 1,4-diazabicyclo(2,2,2)octane, and NIT-mPy is the nitronyl nitroxide 2-(pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, have been synthesized. The molecules of these complexes have a specific combination of the intramolecular ferro- and antiferromagnetic exchange interactions between the odd electrons of Cu(II) and SQ ligands, characterized by large exchange coupling parameters |J| approximately 100-300 cm(-1). X-ray and magnetochemical studies of a series of mixed-ligand compounds revealed that an extra ligand (Py, NIT-mPy, or DABCO) coordinated to the metal atom produces a dramatic effect on the magnetic properties of the complex, changing the multiplicity of the ground state. Quantum chemical analysis of magnetostructural correlations showed that the energy of the antiferromagnetic exchange interaction between the odd electrons of the SQ ligands in the Cu(SQ)2 bischelate is extremely sensitive to both the nature of the extra ligand and structural distortions of the coordination unit, arising from extra ligand coordination.     

Study of electrochemical oxidation of nickel catecholate complexes with bis(diphenylphosphino)ethane by cyclic voltammetry and ESR

One-and two-electron electrochemical oxidation of the (dppe)Ni(Cat) complexes (dppe is bis(diphenylphosphino)ethane, Cat is the sterically hindered catechol dianion) was studied. The transfer of the first electron proceeds reversibly to give paramagnetic species; parameters of their EPR spectra attest to a square planar geometry of one-electron oxidation products. The transfer of the second electron is irreversible because of co-proportionation of radical cations involving the initial complexes and the generated dications. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 99–102, January, 2007.     

3,6-Di-tert-butyl-o-benzosemiquinone complexes of copper(1) with bidentate bis(diphenylphosphine) ligands. Synthesis, structures, and properties

New mononuclear 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(1) with bis(diphenylphosphine) ligands were synthesized: (DBSQ)Cu(dppe) (1) (DBSQ=3,6-di-tert-butyl-o-benzosemiquinone and dppe=1,2-bis(diphenylphosphino)ethane), (DBSQ)Cu(dppp) (2) (dppp=1,3-bis(diphenylphosphino)propane), (DBSQ)Cu(dppn) (3) (dppn=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl), and (DBSQ)Cu(dppfc) (4) (dppfc=1,1′-bis(diphenylphosphino)ferrocene). The compositions and structures of complexes1–4 were characterized by elemental analysis and electronic absorption, IR, and ESR spectroscopy. The molecular structures of complexes3 and4 were established by X-ray diffraction analysis. The reactions of elimination and replacement of neutral ligands in the coordination sphere of the complexes were studied by ESR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2333–2340, November, 1998.     

Synthesis, structures, and properties of 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(i) with 1,5-diaza-3,7-diphosphacyclooctanes

Two new 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(i) (2a and2b) with 1,3,5,7-tetraphenyl-1,5-diaza-3,5-diphosphacyclooctane (1a) and 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (1b), respectively, were synthesized. Their structures in solution and in the crystalline state were studied. According to the results of X-ray diffraction analysis, the copper(i) atom in molecules2a and2b is in a pseudotetrahedral environment and is directly coordinated to two P atoms of the diazadiphosphacyclooctane ligand and two O atoms of the benzosemiquinone ligand. In complex2a, ligand1a adopts a chair-boat conformation typical of all complexes with eight-membered cyclic 1,5-donors studied previously. Unlike ligand1a, the ligand in complex2b adopts a chair-chair (crown) conformation identical with that of the free ligand. Both complexes are paramagnetic in the solid state and in solutions. The parameters of the isotropic ESR spectra of complexes2a and2b are typical of four-coordinateo-semiquinone copper(i) complexes with bidentate bisphosphine ligands. Based on analysis of the isotropic ESR spectra, it was suggested that compound2b in solutions exists as two isomers, which differ in the conformation of the eight-membered heterocycle (chair-boat or chair-chair). Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1806–1812, October, 2000.