Half-Sandwich Rhodium/Iridium(III) Complexes Designed with Cp* and 1,2-Bis(phenylchalcogenomethyl)benzene as Catalysts for Transfer Hydrogenation in Glycerol

The reactions of 1,2-bis(phenylthiomethyl)benzene(L1) and 1,2-bis(phenylselenomethyl)benzene(L2) with [(eta(5)-Cp*)MCl(mu-Cl)](2) (M = Rh or Ir) at room temperature, followed by treatment with NH4PF6 have resulted in air and moisture insensitive half-sandwich complexes of composition [(eta(5)-Cp*)M(L)Cl]-[PF6] (Rh, 1-2; Ir, 3-4; L = L1 or L2). Their HR-MS, H-1, C-13{H-1}, and (77)Ser{H-1} NMR spectra were found to be characteristic. The single crystal structures of 1-4 have been established by X-ray crystallography. The complexes 1-4 have been found efficient for catalytic transfer hydrogenation (TH) of aldehydes and ketones in glycerol, which acts as a solvent and hydrogen source. Complexes 1-2 are the first examples of Rh species explored for TH in glycerol. The catalysis appears to be homogeneous. The complexes of the (Se, Se) ligand are marginally efficient than the corresponding complexes of the (S, S) ligand. The reactivity of Rh complexes in comparison to those of Ir also appears to be somewhat more. The results of DFT calculations appear to be generally consistent with experimental catalytic efficiencies and bond lengths/angles.