SYNTHESIS OF PARAMAGNETIC TETRAKIS(BENZYLISOCYANIDE)BIS(TRI-P-TOLYLARSINE OXIDE)COBALT(III) TETRAFLUOROBORATE - AN EXAMPLE OF OXIDATION OF LIGAND AND METAL IN REACTION OF PENTAKIS(ARYLISOCYANIDE)COBALT(II) WITH TRIARYLARSINE

Golden yellow, paramagnetic [Co(CNCH2Ph)4{OAs(C6H4Me-p)3}2](BF4)3 is synthesized by reaction of [Co(CNCH2Ph)5](BF4)2 with excess As(C6H4Me-P)3 in CH2Cl2 solution. Both AsR3 and Co(II) are apparently rapidly oxidized in this novel reaction, although Co(II) disproportionation has not been excluded. The microcrystalline salt is characterized by IR, electronic spectra, magnetic susceptibility and molar conductivity; stability in solution is limited. Effective magnetic moment of 3.58 BM indicates the intermediate spin state of two unpaired electrons, previously unobserved for Co(III). Simple crystal field rationalization suggests a B-3(2g)[(e(g))4 (b2g)1(a1g)1] ground state, based on tetragonally elongated octahedral coordination. [Co2(CNCH2Ph)10](BF4)4. H2O is synthesized as starting material and characterized; data are consistent with Co-Co bonded dimeric structure in the solid state and [Co(CNCH2Ph)5](BF4)2 monomeric structure in solution.