Synthesis of novel POCN pincer complexes of Nickel (II) and their use as hydrosilylation and hydroboration catalysts

The chemistry of unsymmetrical pincer complexes with different side-arm donors, such as PXN, is known but little studied. Such an unsymmetrical substitution in the sidearm
positions of pincer ligands allows for fine-tuning of stability vs. catalytic activity of pincer complexes, often affecting the selectivity of catalytic transformations.
A series of unsymmetrical iminophosphinite POCN pincer Ni(II) complexes, (POCN)NiMe and (POCN)NiLn(BX4) (L = CH3CN, n = 0, 1; X = F, Ph, C6F5), have been developed and subjected to catalytic hydrosilylation of alkenes, aldehydes and ketones and catalytic hydroboration of carbonyl compounds. The stoichiometric reactivity of (POCN)NiMe and (POCN)Ni(BF4) with PhSiH3 and HBPin suggests that catalytic reactions proceed via the hydride intermediate (POCN)NiH. With regard to reactions with HBPin, efficient and mild hydroboration of a variety of carbonyl compounds,
including the highly chemoselective hydroboration of benzaldehyde in the presence of other common potent reductive functional groups, such as alkenes, alkynes, esters, amides, nitriles, nitro compounds and even ketones, were demonstrated for (POCN)NiMe. We also report the first example of base metal catalyzed hydroboration of amides, including mild direct hydroborative reduction of primary and
secondary amides to borylated amines.