Molecular hydrogen and water activation by transition metal frustrated Lewis pairs containing ruthenium or osmium components: catalytic hydrogenation assays.

The transition metal frustrated Lewis pair compounds [(Cym)M(κ 3 S,P,N-HL1)][SbF 6 ] (Cym = η 6 - p -MeC 6 H 4 iPr; H2L1 = N -( p -tolyl)- N '-(2-diphenylphosphanoethyl)thiourea; M = Ru (5), Os (6)) have been prepared from the corresponding dimer [{(Cym)MCl} 2 (μ-Cl) 2 ] and H2L1 by successive chloride abstraction with NaSbF 6 and AgSbF 6 and NH deprotonation with NaHCO 3 . Complexes 5 and 6 and the previously reported phosphano-guanidino compounds [(Cym)M(κ 3 P,N,N'-HL2)][SbF 6 ] [H2L2 = N , N '-bis( p -tolyl)- N ''-(2-diphenylphosphanoethyl) guanidine; M = Ru (7), Os (8)] and pyridinyl-guanidino compounds [(Cym)M(κ 3 N,N',N''-HL3)][SbF 6 ] [H2L3 = N , N '-bis( p -tolyl)- N ''-(2-pyridinylmethyl) guanidine; M = Ru (9), Os (10)] heterolytically activate H 2 in a reversible manner affording the hydrido complexes [(Cym)MH(H2L)][SbF 6 ] (H2L = H2L1; M = Ru (11), Os (12); H2L = H2L2; M = Ru (13), Os (14); H2L = H2L3; M = Ru (15), Os (16)). DFT calculations carried out on the hydrogenation of complex 7 support an FLP mechanism for the process. Heating 9 and 10 in methanol yields the orthometalated complexes [(Cym)M(κ 3 N,N',C-H2L3-H)][SbF 6 ] (M = Ru (17), Os (18)). The phosphano-guanidino complex 7 activates deuterated water in a reversible fashion, resulting in the gradual deuteration of the three cymene methyl protons through sequential C(sp 3 )-H bond activation. From DFT calculations, a metal-ligand cooperative reversible mechanism that involves the O-H bond activation and the formation of an intermediate methylene cyclohexenyl complex has been proposed. Complexes 5-10 catalyse the hydrogenation of the CC double bond of styrene and a range of acrylates, the CO bond of acetophenone and the CN bond of N -benzylideneaniline and quinoline. The CC double bond of methyl acrylate adds to catalyst 9, affording complex 19 in which a new ligand exhibiting a fac κ 3 N,N',C coordination mode has been incorporated.