Catalytic amine-borane dehydrogenation by a PCP-pincer palladium complex: A combined experimental and DFT analysis of the reaction mechanism

摘要

Catalytic dehydrogenation of ammonia-borane (NH_3·BH _3, AB) and dimethylamine borane (NHMe_2·BH _3, DMAB) by the Pd~(II) complex [(~(tBu)PCP)Pd(H _2O)]PF_6 [~(tBu)PCP = 2,6-C_6H _3(CH_2P~tBu_2)_2] leads to oligomerization and formation of spent fuels of general formula cyclo-[BH _2-NR_2]_n (n = 2,3; R = H, Me) as reaction byproducts, while one equivalent of H_2 is released per amine-borane equivalent. The processes were followed through multinuclear (~(31)P, ~1H, ~(11)B) variable temperature NMR spectroscopy; kinetic measurements on the hydrogen production rate and the relative rate constants were also carried out. One non-hydridic intermediate could be detected at low temperature, whose chemical nature was explored through a DFT modeling of the reaction mechanism, at the M06//6-31+G(d,p) computational level. The computational output was of help to propose a reliable mechanistic picture of the process.