ONE-ELECTRON TRANSFORMATIONS OF PARAMAGNETIC COBALT COMPLEXES - SYNTHESIS AND STRUCTURE OF COBALT(II) AMIDODIPHOSPHINE HALIDE AND ALKYL COMPLEXES AND THEIR REACTION WITH ALKYL-HALIDES

Complexes of the type CoX[N(SiMe2CH2PPh2)(2)], where X = Cl, Br, or I, can be prepared via reaction of CoX2 with LiN(SiMe2CH2PPh2)(2); these derivatives are tetrahedral high-spin d(7) systems. Reaction of these halide complexes with organolithium, sodium, or potassium reagents ge nerates square-planar, low-spin hydrocarbyl complexes of the formula C oR[N(SiMe2CH2PPh2)(2)] (R = Me, CH2Ph, CH2SiMe3, C5H5). One-electron o xidations have been carried out; only the product of halide abstractio n is observed. For example, addition of PhCH2X to the halide derivativ es CoX[N(SiMe2CH2PPh2)(2)] generates trivalent, paramagnetic complexes , CoX2[N(SiMe2CH2PPh2)(2)]; these derivatives show variable-temperatur e magnetic susceptibility data that are consistent with zero-field spl itting of the S = 1 state. Addition of methyl bromide or methyl iodide to low-spin CoMe[N(SiMe2CH2PPh2)(2)] results in the formation of the Co(II) halide derivatives CoX[N(SiMe2CH2PPh2)(2)] along with methane a nd bibenzyl. It is proposed that the Co(III) methyl halide complex CoM e(X) [N(SiMe2CH2PPh2)(2)] is unstable and loses methyl radical homolyt ically to generate the Co(II) halide derivative; the methyl subsequent ly reacts with the toluene solvent to produce methane and bibenzyl. Ad dition of excess benzyl halides has also been found to generate the Co (II) halide complexes initially, followed by a one-electron oxidation to the Co(II) dihalide derivatives. In much of the one-electron chemis try of the Co(II) derivatives incorporating the amidodiphosphine ligan d, the decomposition of the putative but unstable Cs(III) alkyl halide derivative CoRX[N(SiMe2CH2PPh2)(2)] is proposed as a recurring event.