PdII and PtII complexes bearing acetamide and thioacetamide functionalized heteroscorpionates and their application in the hydrosilylation of terminal alkynes

Abstract

Reaction of ligand N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide (pbptamH) with MCl₂ (M = Pd, Pt) in acetonitrile results in the formation of cationic complexes 1a-b with the general formula [(pbptamH)₂M]Cl₂. If the former reaction is modified by the addition of K₂CO₃, neutral complexes 2a-b with the formula [(pbptam)₂M] are obtained in excellent yields. Both types of complexes, neutral and cationic complexes 1 and 2, display coordination to the metal centers via the thioacetamide sulfur atom and one pyrazole moiety. Additionally, the stoichiometric treatment of ligand N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide (pbpamH) with MCl₂ (M = Pd, Pt) results in the generation of monoligated complexes 3a-b with the general formula [(pbpamH)MCl₂] in which the metal center is stabilized via coordination of two pyrazolyl fragments in a chelating fashion. If ligand pbpamH is treated with half an equivalent of MCl₂ (M = Pd, Pt) in the presence of excess NaBF₄, cationic complexes 5a-b of the type [(pbpamH)₂M](BF₄)₂ are generated. The reaction conditions, isolation, and characterization of the products are discussed in detail. The palladium and platinum complexes were tested in the hydrosilylation of terminal alkynes, unveiling complex 3b as the best of the series with excellent conversions under low catalyst loadings and good selectivity toward the E isomer.