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)₂Fe­(μ-^MePyr)­(μ-CO)­Fe­(NO)₂] (3-K-crown, ^MePyr = 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)₂Fe­(N,N′-^MePyrBH₂NMe₂)]⁻ (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)₂Fe­(μ-CO)₂Fe­(NO)₂]⁻ (6) is synchronized with the deactivated generation of H_2(g). Through reaction of complex [Na-18-crown-6-ether]­[(NO)₂Fe­(η²-BH₄)] (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)₂Fe­(μ-^MePyr)­(μ-CO)­Fe­(NO)₂]⁻ (3) into the iron-hydride species A as an intermediate during the generation of H_2(g).