Reversible, Metal-Free Hydrogen Activation

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Abstract
Although reversible covalent activation of molecular hydrogen (H 2 ) is a common reaction at transition metal centers, it has proven elusive in compounds of the lighter elements. We report that the compound (C 6 H 2 Me 3 ) 2 PH(C 6 F 4 )BH(C 6 F 5 ) 2 (Me, methyl), which we derived through an unusual reaction involving dimesitylphosphine substitution at a para carbon of tris(pentafluorophenyl) borane, cleanly loses H 2 at temperatures above 100°C. Preliminary kinetic studies reveal this process to be first order. Remarkably, the dehydrogenated product (C 6 H 2 Me 3 ) 2 P(C 6 F 4 )B(C 6 F 5 ) 2 is stable and reacts with 1 atmosphere of H 2 at 25°C to reform the starting complex. Deuteration studies were also carried out to probe the mechanism.