Ruthenium Complexes Containing Pyridinyl-Derived Ligands as FLP Catalysts

We report the synthesis of ruthenium-based frustrated Lewis pair (FLP) complexes of the general formula [(Mes)Ru(κ3N,N′,N″-L)][SbF6], where Mes denotes η6-1,3,5-C6H3Me3 and L corresponds to two different ligands: L1 (N,N′-bis(2,6-diisopropylphenyl)-N″-(2-pyridinylmethyl)guanidinate) in complex 1 and L2 (N-2-pyridinyl-N-(2-pyridinylmethyl)amidate) in complex 4. These complexes are obtained from the dimer [{(Mes)RuCl}2(μ-Cl)2] in combination with HL1 or HL2 under chloride abstraction and deprotonation conditions. Complexes 1 and 4 undergo reversible heterolytic activation of H2 to form the corresponding hydrido species [(Mes)RuH(κ2N,N′-HL)][SbF6] (HL = HL1 for complex 6; HL2 for complex 7). The formation of these hydrido complexes is observed in both the hydrodechlorination of chlorinated substrates under H2 and the base-free dehydrogenation of formic acid, highlighting the reversibility of hydrogen activation within this TMFLP framework. Finally, complexes 1 and 4 act as transition-metal frustrated Lewis pair (TMFLP) hydrogenation catalysts and catalyze the hydrogenation reaction of C═C bonds in acrylates (even in water for 1), as well as the C═O bond of 2,2,2-trifluoroacetophenone, and the C═N bond of N-benzylideneaniline.