New [Ir(CH 3 CN) 2 (I) 2 {κC,C′-bis(NHC)}]BF 4 complexes featuring bis-NHC ligands with a methylene bridge and different N substitution (−CH 2 CH 2 CH 2 CH 3 and −CH 2 CH 2 OPh) were synthesized. NMR studies and X-ray diffraction structures evidenced that the wingtip group −CH 2 CH 2 OPh presents a hemilabile behavior in solution, with the oxygen atom coordinating and dissociating at room temperature, which contrasts with the strong coordination of the ether functions in the complex [Ir-(I) 2 {κC,C′,O,O′-bis(NHC OMe )}]BF 4 (bis(NHC OMe ) = methylenebis(N,N′-bis(2-methoxyethyl)imidazol-2-ylidene)), previously reported by us. These complexes proved to be efficient catalysts for the hydrolysis and methanolysis of silanes, affording molecular hydrogen and silyl alcohols or silyl ethers as the main reaction products in excellent yields. The hydrogen generation rates were very much dependent on the nature of the hydrosilane and the coordination ability of the wingtip group. The latter also played a key role in the recyclability of the catalytic system.

Complex [OsH(η2-H2)(η2-CH2CH-o-C5H4 N)(PiPr3)2]BF4 (1) reacts with methyl vinyl ketone in the absence of solvent to give [OsH{CHCHC(O)CH3}2(P i Pr3)2]BF4 (2), which can be described as two osmafurans joined by a common [OsH(P i Pr3)2]+ fragment. The hydride ligand of 2 is fairly acidic. Thus, its treatment with sodium methoxide produces the deprotonation of the metal center to give Os{CHCHC(O)CH3}2(P i Pr3)2 (3). The reaction is not reversible; the protonation of 3 with HBF4·OEt2 leads to [ Os{CHCHC(O)CH3}{CHCH2C(O)CH3}(P i Pr3)2]BF4 (4), which in dichloromethane is unstable and evolves into [Os{CHCHC(O)CH3}Cl{CCHC(CH3)OH}(P i Pr3)2]BF4 (5), containing an enolcarbyne ligand. In the solid state the anion of 5 is associated with the OH-hydrogen of the enol, by means of an H···F hydrogen bond. In dichloromethane the H···F hydrogen bond is broken and DFT calculations suggest that the OH-hydrogen atom forms an H···Cl hydrogen bond with the chlorine ligand. In the absence of solvent, complex 1 reacts with benzylideneacetophenone and benzylideneacetone to give [Os{C(Ph)CHC(O)R}(η2-H2){κ-C-[HNC5H3Et]}(P i Pr3)2]BF4 (R = Ph (6), CH3 (10)), containing a NH-tautomerized 2-ethylpyridine ligand. Complexes [Os{C(Ph)CHC(O)R}(η2-H2){(CH3CN)}(P i Pr3)2]BF4 (R = Ph (8), CH3 (11)) and [Os{C6H4C(O)CHCHPh}(η2-H2){(CH3CN)}(P i Pr3)2]BF4 (9) have been also isolated and characterized. The X-ray structures of 2, 5, and 6 are reported.

The iridium(III) complex [Ir(H)(CF3SO3)(NSiN)(coe)] (NSiN = bis(pyridine-2-yloxy)methylsilyl fac-coordinated) has proven to be an effective catalyst precursor for hydrogen production from the hydrolysis of hydrosilanes at room temperature. The reaction performance depends both on the silane nature and the solvent. Interestingly, high TOF values of around 10 5 h-1 were obtained using Et2SiH2 or (Me2HSi)2O as hydrogen sources and THF as solvent. Moreover a mechanistic insight of this iridium-catalyzed hydrogen generation process, based on both theoretical calculations and NMR studies, is reported. The overall catalytic cycle can be view as a two stages process involving i) the water promoted Si-H bond activation which is followed by ii) the water splitting via a proton transfer.