Electron Exchange Along the Tercyclopentadienyltrimetallic Scaffold: Kinetics, Equilibria, and Bond Strengths

摘要

Electron transfer is fundamental to chemical reactivity. A prototype example in organometallic chemistry is the attack of an anionic metal center on a metal-metal bond (M'- + M'-M'), which by nucleophilic substitution should lead to M-M' + M~-. Such a result is not cleanly found, however, as the outcome of this mechanistically complex transformation is usually controlled by thermodynamic factors through electron redistribution to provide M-M + M'~-. We report the first direct observation of such equilibria for cyclopentadienyl (Cp) metal complexes using NMR spectroscopy, mechanistic studies, and the use of the data for the estimation of CpM-M'Cp bond strengths. Key to these results is the employment of the tercyclopentadienyl (terCp) ligand as a frame on which to render the desired transformations intramolecular and regiospecific (Scheme 1).