The mechanisms of protonation of [M(η5-C5H5)2H2](M = Mo or W)

Abstract

The reaction between [M(η⁵-C₅H₅)₂H₂](M = Mo or W) and an excess of anhydrous HCl occurs by essentially the same mechanism for the two complexes. Protonation of the tungsten complex involves initial attack at a hydride ligand to generate the spectroscopically detected [W(η⁵-C₅H₅)₂H(η²H₂)]⁺, which subsequently undergoes an intramolecular oxidative cleavage of the dihydrogen ligand to give the trihydride, [W(η⁵-C₅H₅)₂H₃]⁺. The kinetic and thermodynamic isotope effects associated with these elementary reactions have been determined. Protonation of the analogous molybdenum complex also involves initial attack at a hydride ligand. However, in this system kinetic and spectroscopic studies indicate that the subsequent cleavage of the dihydrogen ligand to form [Mo(η⁵-C₅H₅)₂H₃]⁺. occurs via the rapid formation of a detectable binuclear species which is probabaly [{Mo(η⁵-C₅H₅)₂H₂}₂(µ-H)]⁺.