Bidentate bis(NHC-carboxylate) palladium and nickel complexes for the hydrosilylative reduction of carbonyl compounds.

A family of 16 e- Pd(ii) and Ni(ii) biscarbenes bearing NHC ligands decorated with different amino acids in the side chain has been synthesized. The Pd complexes were accessible through transmetalation with silver carbenes generated in situ, while the Ni species were obtained by deprotonation of the imidazolium salt with LDA, followed by complete ligand substitution in [NiBr2(dme)]. The new complexes have been studied as catalysts in the reductive hydrosilylation of aldehydes and ketones with phenylsilane, followed by a hydrolysis step to form the corresponding alcohol. One of the nickel biscarbene complexes proved to be a competent catalyst, in which the presence of the carboxylate moieties appears to be beneficial. A DFT study of the electronic and steric properties of NHC-carboxylate ligands has been carried out to identify the key features of the complex that exhibits the highest catalytic activity.