Preparation and Reactivity of Sigma-Complexes

Abstract

Ligation of molecular hydrogen to transition metal complexes was first observed by Kubas and co-workers in 1984. In this work, three-coordinate pincer ligands were employed in the preparation of square-planar d8 nickel and palladium dihydrogen complexes. The synthesis, isolation, characterization, and reactivity of these hydrogen-ligated group 10 complexes is reported. Solution nuclear magnetic resonance (NMR) spectroscopy was used to accurately determine the H-H distance in the ligand based on measurements of both T1 and 1JHD. Relevant to understanding the degree of bond activation occurring at a transition metal, these dihydrogen complexes can be models for important intermediates in homogeneous catalytic processes. Additionally, silylium (silyl arenium) cations were synthesized, characterized, and employed in the synthesis of the dihydrogen complexes. A crystal structure of the triethylsilane- bound triethylsilylium ion, [(Et3Si)2H]+ is included.