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

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.