Electrophilic Addition vs Electron Transfer for the Interaction of Ag+ with Molybdenum(II) Hydrides. 1. Reaction with CpMoH(PMe3)3 and the Mechanism of Decomposition of [CpMoH(PMe3)3]+

The compound CpMoH(PMe 3 ) 3, 1, is oxidized by Ag + in acetonitrile to the 17-electron complex [CpMoH(PMe 3 ) 3 ] +, [ 1 ] +, which is indefinitely stable at low temperature. The oxidation takes place without the observation of a silver adduct intermediate. Complex [ 1 ] + has also been generated by ferrocenium oxidation or by anodic oxidation and characterized by EPR spectroscopy. Complex [ 1 ] + slowly decomposes at room temperature by a second-order rate law ( v = k disp [ 1 + ] 2 ), consistent with a disproportionation mechanism. In the presence of unoxidized 1, on the other hand, the decomposition of [ 1 ] + is faster and proceeds via a deprotonation mechanism ( v = k deprot [ 1 + ][ 1 ]) with compound 1 acting as a catalyst. The ratio of the two second-order rate constants is k deprot / k disp = 5.8(7)). Intermediates of the disproportionation pathway, the solvent-stabilized double-oxidation products [CpMoH(S)(PMe 3 ) 3 ] 2+ (S = THF, MeCN), have been isolated as stable salts with the PF 6 - and BF 4 - counterions, respectively. The acetonitrile adduct has also been characterized by X-ray crystallography. The complex [CpMoH(MeCN)(PMe 3 ) 3 ] 2+ slowly transfers a proton to complex 1 to afford a 1:1 mixture of [CpMo(PMe 3 ) 3 (MeCN)] + and [CpMo(PMe 3 ) 3 H 2 ] + and is also slowly deprotonated by NEt 3 .