Bimetallic Aluminum Hydride s-Block (Li, Na, K) Compounds in Catalytic Hydroboration

Hydroboration is an important transformation for preparing synthetic intermediates that participate in numerous reactions. While traditionally catalyzed by transition metals, the pursuit of more sustainable methodologies has prompted the development of catalysts based on earth-abundant elements. Aluminum hydrides have been employed as (pre)catalysts for the hydroboration of unsaturated functional groups, exhibiting enhanced activity in their ate complexes through alkali-metal cooperativity, yet the identity of the active species, particularly in carbonyl hydroboration, remains under debate. Herein, we report the isolation and full characterization of a series of alkali metal (Li, Na, and K) aluminate hydride complexes with bis(aminophosphino-borane)naphthalene as a supporting ligand. We explore and benchmark their catalytic activity in the hydroboration of benzophenone and phenylacetylene using pinacolborane (HBpin). The role of the aluminates, the origin of synergistic effects, and the proposed reaction mechanisms are examined through stoichiometric studies, the isolation of intermediates, and DFT calculations.