Hydrolysis and Methanolysis of Silanes Catalyzed by Iridium(III) Bis-N-Heterocyclic Carbene Complexes: Influence of the Wingtip Groups

New
[Ir­(CH3CN)2(I)2{κC,C′-bis­(NHC)}]­BF4 complexes
featuring bis-NHC ligands with a methylene bridge and different N
substitution (−CH2CH2CH2CH3 and −CH2CH2OPh) were synthesized.
NMR studies and X-ray diffraction structures evidenced that the wingtip
group −CH2CH2OPh 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(NHCOMe)}]­BF4 (bis­(NHCOMe) = 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.