Alkali Metal Complexes as Efficient Catalysts for Hydroboration and Cyanosilylation of Carbonyl Compounds

Panda, Tarun K and A, Harinath and Bhattacharjee, J and Nayek, Hari Pada (2018) Alkali Metal Complexes as Efficient Catalysts for Hydroboration and Cyanosilylation of Carbonyl Compounds. Dalton Transactions. ISSN 1477-9226

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Abstract

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 (AeI2) in a 2:2:1 molar ratio, which resulted in the formation of a heteroleptic Ae metal complex [2-{2-(AdN=CH)-C4H3N}2Ae(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 aldehyde/ketones, using the alkali metal precatalyst 3 under mild conditions. In both catalytic processes, the potassium catalyst 3 exhibited a high tolerance towards a number of functional groups. First-order kinetics with respect to catalyst 3 and each of the substrates was observed for the hydroboration reaction of carbonyl compounds catalysed by alkali metals.

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