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; H 2 L1 = 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 H 2 L1 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 ] [ H 2 L2 = 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 ] [ H 2 L3 = 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( H 2 L )][SbF 6 ] ( H 2 L = H 2 L1 ; M = Ru ( 11 ), Os ( 12 ); H 2 L = H 2 L2 ; M = Ru ( 13 ), Os ( 14 ); H 2 L = H 2 L3 ; 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- H 2 L3 -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&z.dbd;C double bond of styrene and a range of acrylates, the C&z.dbd;O bond of acetophenone and the C&z.dbd;N bond of N -benzylideneaniline and quinoline. The C&z.dbd;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. Masked transition metal frustrated Lewis pairs containing ruthenium and osmium components activate a variety of bonds of small molecules.