Selective Synthesis of Various Photofunctional Multinuclear Complexes Using a Combination of the Mizoroki–Heck Reaction and the Homo-coupling Reaction

Abstract

As described in Chap. 2, the Mizoroki–Heck reaction between metal complexes with bromo groups and those with vinyl groups in the diimine ligand did not proceed using Pd(OAc)₂ and a tertiary phosphine ligand under an Ar atmosphere. However, it proceeded selectively after the injection of air into the reaction vessel. In this chapter, I report the effect of the air injection on the Pd compounds for the coupling reactions in detail. Interestingly, the Mizoroki–Heck reaction took place even in the absence of the phosphine ligand. However, a homo-coupling reaction between the metal complexes with bromo groups proceeded at the same time. Mechanistic investigation showed that nanoparticles of Pd species were produced in the absence of the phosphine ligand and functioned as catalysts for both the Mizoroki–Heck and homo-coupling reactions. In contrast, larger Pd particles, which were produced in the presence of the phosphine ligands but after the addition of air for oxidizing the phosphine ligands, catalyzed the Mizoroki–Heck reaction with high selectivity. Based on these results, reaction conditions were established for the selective progress of the Mizoroki–Heck and the homo-coupling reactions.