Electron transfer versus nucleophilic pathways in the ion-pair annihilation of organoborate anions by carbonylmanganese(I) cations

Substituted carbonylmanganese cations [Mn(CO)(5)L](+), where L = py, PPh3 a nd PPh2Me, readily react with various organoborate anions (tetramethylborat e, methyltriphenylborate and tetraphenylborate) in THF solution to afford a mixture of dimanganese carbonyls, hydridomanganese carbonyls and alkylmang anese carbonyls. The formation of the dimanganese carbonyl dimers as well a s the hydridomanganese carbonyls suggests the involvement of 19-electron ca rbonylmanganese radicals that stem from an initial electron transfer. On th e other hand, the acetonitrile-substituted analogue [Mn(CO)(5)(CH3CN)](+) r eacts with the same berate anions to afford the alkylated RMn(CO)(5), where R = CH3 and C6H5, as the sole carbonylmanganese product. As such, this alk ylative annihilation is best formulated as a direct attack on the carbonyl carbon by the berate nucleophile. The two different pathways can be underst ood in terms of the balance between the electrophilicity of the carbonyl li gand and the electron affinity of the carbonylmanganese cation. (C) 1999 El sevier Science S.A. All rights reserved.