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
posted on 2022-12-29, 21:07authored byYu-Ting Tseng, Vladimir Pelmenschikov, Linda Iffland-Mühlhaus, Donato Calabrese, Yu-Che Chang, Konstantin Laun, Chih-Wen Pao, Ilya Sergueev, Yoshitaka Yoda, Wen-Feng Liaw, Chien-Hong Chen, I-Jui Hsu, Ulf-Peter Apfel, Giorgio Caserta, Lars Lauterbach, Tsai-Te Lu
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 H2(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 H2(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
H2(g).