Generation of Mono- and Bimetallic Palladium Complexes and Mechanistic Insight into an Operative Metal Ring-Walking Process

Abstract

This combined experimental and computational study demonstrates how a metal center can drastically influence the reactivity of a coordinated ligand. We found that the consecutive formation of zerovalent bimetallic complexes proceeds by fast η2-C═C coordination of only one Pd(PEt3)2 moiety, which then significantly slows down the subsequent reaction. Electronic effects induced by complexation of the first metal center have a major effect on the subsequent formation of the bimetallic complexes. These effects are reduced by partial fluorination of the bis(vinylpyridine)-arene ligand. The monometallic complexes display migration of the Pd(PEt3)2 moiety between the two olefinic bonds of the corresponding ligand, as indicated by various solution NMR experiments, including variable-temperature NMR spectroscopy, 2D 1H–1H exchange spectroscopy, and spin saturation transfer. Density functional theory studies were performed at the SMD(toluene)–PBE0+d(v3)/B2//B97D/B1 level of theory.