Cobalt sandwich-stabilized rhodium nanocatalysts for ammonia borane and tetrahydroxydiboron hydrolysis

Abstract

Evolution of H₂ upon catalytic hydrolysis of inorganic hydrides is a key method for clean energy production. Here, a new organocobalt precursor is used to generate nanocatalysts that are efficient, stable and recyclable. The cobalt complexes [Co(η⁵-C₅H₅)(η⁴-C₅H₆)], 1, and [Co(η⁵-C₅Me₅)(η⁴-C₅H₆)], 2, are used to reduce late transition metal chlorides to a series of late transition metal nanoparticles, abbreviated TMNP and TMNP*, respectively, that catalyse hydrolysis of B₂(OH)₄ and ammonia borane (AB). Among the prepared TMNP and TMNP*, the latter are found to be the most efficient and recyclable catalysts, showing, with RhNP*, TOFs of 1364 mol_H2 mol_cat⁻¹ min⁻¹ in B₂(OH)₄ hydrolysis and 125 mol_H2 mol_cat⁻¹ min⁻¹ in AB hydrolysis at a low catalyst loading of 0.2 mol%. The kinetic study including kinetic isotope effect leads to a proposed mechanism of the RhNP*-catalysed AB hydrolysis involving water O–H bond oxidative addition on the catalyst surface as the rate-limiting step for H₂ generation.