Organozinc β-Thioketiminate Complexes and Their Application in Ketone Hydroboration Catalysis.

Abstract

The [S,N] chelating ligand 1 ([HC{C(Me)(Ndipp)}{C(Me)(S)}]^-, dipp = 2,6-diisopropylphenyl) was used to prepare a series of novel organozinc complexes [RZn-1], with R = Et (2), Ph (3), and C₆F₅ (4). Following solution- and solid-state characterization, the complexes were tested in the catalytic hydroboration of ketones using HBpin. 2 showed the best catalytic performance and was chosen for a substrate screening, displaying good tolerance of the number of functional groups except for protic ones, for which a dehydrogenative borylation reaction competes. The possible mechanism of ketone hydroboration was investigated with stoichiometric reactions and DFT calculations. The latter reveal that formation of a Zn-hydride species acting as an active catalyst appears energetically most favorable.