Ligand Influence on Carbonyl Hydroboration Catalysis by Alkali Metal Hydridotriphenylborates [(L)M][HBPh3] (M=Li, Na, K)

Alkali metal hydridotriphenylborates [(L1)M][HBPh3] (L1 = Me6TREN; M = Li, Na, K) chemoselectively catalyze the hydroboration of carbonyls and CO2, with lithium being the most active system. A new series of complexes [(L2)M][HBPh3] [M = Li (1), Na (2), K (3)] with the cyclen-derived macrocyclic polyamine Me4TACD (L2) were synthesized in a 'one-pot' fashion and fully characterized including X-ray crystallography. In the crystal, 1-3 exhibit wide variation in metal coordination of the [HBPh3] anion from lithium to potassium. The structures differ from those in [(L1)M][HBPh3]. Effects of coordination of L1, L2, and other N- and O-donor multidentate ligands on [Li(HBPh3)] were used to rationalize the catalytic activity in carbonyl hydroboration.