金属羰基化合物M(CO)_6(M=Cr,Mo,W)氧原子转移反应动力学与机理

A Study of Kinetics and Mechanism of Oxygen Atom Transfer Reaction of M(CO)_6(M=Cr, Mo, W)

本文研究了PPh_3存在与不存在的情况下,M(CO)_6(M=Cr,Mo,W)与三甲胺氧化物Me_3NO在CH_2Cl_2中的氧原子转移反应动力学。反应速率遵循:r=k[M(CO)_6][Me_3NO],并且,r_W>r_(Mo)>r_(Or)。并根据实验结果提出了反应机理,讨论了溶剂对反应速率的影响。

This paper reports the kinetics for the reactions of M(CO)_6 (M=Cr, Mo, W) with Me_3NO, in the absence and in the presence of triphenylphosphine (PPh_3). The rates of reaction are first-order in concentrations of M(CO)_6 and Me_3NO, but zero order in PPh_3 concentration. The rates of reaction decrease in the order W>Mo≥Cr. The solvent effect shows an increase in rate with increasing dielectric strength of the solvent. A mechanism is proposed which involves attack on a carbonyl carbon with the formation of coordinatively unsaturated intermediates of the type M(CO)_5, which then rapidly react with an entering ligand. Compared with other nucleophiles reported to react by carbonyl attack in M(CO)_6 substrates, Me_3NO is a strong nucleophile. Qualitatively, the nucleophilic strengths decrease in the order: MeLi>Me_3NO≥PhCH_2MgBr》N_3^->NCO^-> NCS^->Cl^->Br^->I^-.