Alkali metal complexes as efficient catalysts for hydroboration and cyanosilylation of carbonyl compounds

摘要

We report here reactions between the N-adamantyliminopyrolyl ligand 2-(AdN=CH)-C4H3NH (L-H) and alkali metal hexamethyldisilazides [MN(SiMe3)(2)] (M = Li, Na and K) to afford the dimeric [{2-(AdN=CH)-C4H3NLi(THF)}(2)] (1), [{2-(AdN=CH)-C4H3N){Na(THF)(1.5)}(2)] (2) and polymeric [{2-(AdN=CH)-C4H3NK(THF)}(n)] (3) complexes at ambient temperature. A one-pot reaction between L-H, [KN(SiMe3)(2)] and alkaline earth metal diiodide (Ael(2)) in a 2 : 2 :1 molar ratio, which resulted in the formation of a heteroleptic Ae metal complex [kappa(2)-{2-(AdN=CH)-C4H3N}(2)Ae(THF)(2)] [Ae = Mg (4), Ca (5)], is also reported. The solid-state structures of complexes 1, 3 and 4 were established through single-crystal X-ray diffraction analysis. The alkali and alkaline earth metal complexes 1-5 were utilised as precatalysts for the catalytic hydroboration of pinacolborane (HBpin) with aldehydes and ketones, and potassium complex 3 was identified as a competent catalyst under mild conditions. Additionally, cyanosilylation of carbonyl compounds was explored with trimethylsilyl cyanide and aldehydes/ketones, using the alkali metal precatalyst 3 under mild conditions. In both catalytic processes, the potassium catalyst 3 exhibited high tolerance towards a number of functional groups.