Substrate-Gated Transformation of a Pre-Catalyst into an Iron-Hydride Intermediate [(NO) 2 (CO)Fe(μ-H)Fe(CO)(NO) 2 ] - for Catalytic Dehydrogenation of Dimethylamine Borane.

Continued efforts are made on the development of earth-abundant metal catalysts for dehydrogenation/hydrolysis of amine boranes. In this study, complex [K-18-crown-6-ether][(NO) 2 Fe(μ- Me Pyr)(μ-CO)Fe(NO) 2 ] ( 3-K-crown , Me Pyr = 3-methylpyrazolate) was explored as a pre-catalyst for the dehydrogenation of dimethylamine borane (DMAB). Upon evolution of H 2(g) from DMAB triggered by 3-K-crown , parallel conversion of 3-K-crown into [(NO) 2 Fe( N , N '- Me PyrBH 2 NMe 2 )] - ( 5 ) and an iron-hydride intermediate [(NO) 2 (CO)Fe(μ-H)Fe(CO)(NO) 2 ] - ( A ) was evidenced by X-ray diffraction/nuclear magnetic resonance/infrared/nuclear resonance vibrational spectroscopy experiments and supported by density functional theory calculations. Subsequent transformation of A into complex [(NO) 2 Fe(μ-CO) 2 Fe(NO) 2 ] - ( 6 ) is synchronized with the deactivated generation of H 2(g) . Through reaction of complex [Na-18-crown-6-ether][(NO) 2 Fe(η 2 -BH 4 )] ( 4-Na-crown ) with CO (g) as an alternative synthetic route, isolated intermediate [Na-18-crown-6-ether][(NO) 2 (CO)Fe(μ-H)Fe(CO)(NO) 2 ] ( A-Na-crown ) featuring catalytic reactivity toward dehydrogenation of DMAB supports a substrate-gated transformation of a pre-catalyst [(NO) 2 Fe(μ- Me Pyr)(μ-CO)Fe(NO) 2 ] - ( 3 ) into the iron-hydride species A as an intermediate during the generation of H 2(g) .