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 n²-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.