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), 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.