(PYRIDINE)BIS(8-QUINOLINATO)OXOVANADIUM(IV) - FREE-RADICAL-LIKE METAL CENTER IN REACTIONS WITH DIOXYGEN, PARA-BENZOQUINONE, AND AROMATIC NITROSO-COMPOUNDS

A novel synthesis of bis(8-quinolinato)oxovanadium(IV), VOQ2 (Q = 8-quinolinato anion), and the corresponding pyridine adduct, pyVOQ2, is reported. Although both have been found to be reactive in one-electron redox processes, pyVOQ2,which is soluble in organic solvents, was used as a model compound. pyVOQ2 reacts very easily at room temperature and atmospheric pressure with O2 producing the diamagnetic dinuclear M-OXO complex [Q2OV-O-VOQ2]. When O2 is replaced by p-benzoquinone in the same reaction, the dinuclear diamagnetic vanadium(V) complex [Q2OVO-C6H4-OVOQ2] is obtained. The high affinity for oxygen along with the tendency to achieve both the +5 oxidation state and hexacoordination by vanadium in these complexes could be the driving force for the observed vanadium-promoted deoxygenation of aromatic nitroso compounds. pyVOQ2 reacts with nitrosobenzene and 2-nitrosobiphenyl (ArNO) in a tetrahydrofuran (THF) solution giving [Q20V-0-V0Q2] and the corresponding azoxy derivatives (ArN(0)=NAr). The deoxygenation of 2-nitrosobiphenyl with P(OR)3 produces only carbazole, which is supposed to be originated by a singlet nitrene, while the deoxygenation by pyVOQ2 gives azoxybiphenyl without traces of carbazole. © 1979, American Chemical Society. All rights reserved.