Fe(II) Hydride Complexes for the Homogeneous Dehydrocouplingof Hydrazine Borane: Catalytic Mechanism via DFT Calculations andDetailed Spectroscopic Characterization

The catalytic dehydrocoupling of hydrazine borane (N2H4·BH3, HB) using two molecularly defined PNP Fe(II) hydride complexes [(PNHP)Fe(HBH3)(H)(CO)] (PNHP = HN[CH2CH2P(i-Pr)2], 1-BH3) and [(PNP)Fe(H)(CO)] (PNP = N[CH2CH2P(i-Pr)2], 2) is reported. Both catalysts are highly active and recyclable, and they can potentially release up to 2.56 equiv of hydrogen from HB, giving a thermally unstable solid dehydrocoupling product. For the stable dehydrogenation of HB of up to 1.0 equiv of hydrogen, we have analyzed the resulting insoluble BxNyHz polymeric residue using 11B solid-state NMR spectroscopy techniques combined with density functional theory (DFT) calculations of 11B NMR parameters for a comprehensive library of molecular BxNyHz fragments compatible with the polymeric BxNyHz structure. These studies were further supported by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. On this basis, we propose a detailed mechanism for the stable dehydrogenation of HB of up to 1.0 equiv of hydro...