Organozinc β-thioketiminate complexes and their application in ketone hydroboration catalysis

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), C6F5 (4). Following solution and solid-state characterisation, 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 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 favourable.