PREPARATION OF ARSENOCOBALOXIMES AND THE CRYSTAL-STRUCTURE OF [(CH3)(C6H5)AS(O)COIII(DMGH)(DMG)]2COII

The Co(I) cobaloxime (C4H9)3PCo(dmgH)2 [dmg H = dimethylglyoximato monoanion] reacts with (CH3)2AsCl, (CH3)2AsI, C6H5AsCl2, (C6H5)(CH3)AsCl, and (C6H5)2AsCl to give solutions of the air-sensitive species R''R"AsCo(dmgH)2P(C4H9)3. When R'' = R" = CH3 and R'' = C6H5, R" = Cl, the ultimate product is {[(C4H9)3P]2Co(dmgH)2}+ X- (X = Cl, I). When R'' = C6H5 and R" = C6H5, CH3, a red solid can be isolated of formula [R''R" As (O)Co(dmg2H)P(C4H9)3]2Co which is hydrated (2H2O) in the case R'' = C6H5, R" = CH3. The crystal structure of a hydrated complex (final R1 = 0.102) consists of 2 (C6H5)(CH3)AsOCo(dmg2H)P(C4H9)3 units which are bonded in a fac configuration to a central Co(II) atom through the arsenyl O and 2 adjacent dmg O atoms. The average Co(II)-O bond length (6 bonds) is 2.08 .ANG.. The 2 Co(III) atoms are axially bound to (C4H9)3P and (C6H5)(CH3)As(O) units. The molecule has approximate (noncrystallographic) 2-fold symmetry and is dissymmetric. Solutions of (CH3)2AsCo(dmgH)2P(C4H9)3 react with CH3I and CH3Co(dmgH)2C5H5N to give (CH3)3As and methyl-cobalt complexes. The CH3 group of CH3Co(dmgH)2C5H5N is not transferred to arsenic on reaction with AsH3 (CH4 is evolved) or AsX3 ([CH3Co(dmgH2)2C5H5N]2+2X-, X = Cl or I, is proposed). The relevance of these reactions to models for the biological methylation of As is discussed.