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

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posted on 2014-05-27, 00:00 authored by Om Prakash, Kamal Nayan Sharma, Hemant Joshi, Pancham L. Gupta, Ajai K. Singh
The reactions of 1,2-bis­(phenylthiomethyl)­benzene­(L1) and 1,2-bis­(phenylselenomethyl)­benzene­(L2) with [(η5-Cp*)­MCl­(μ-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 [(η5-Cp*)­M­(L)­Cl]­[PF6] (Rh, 12; Ir, 34; L = L1 or L2). Their HR-MS, 1H, 13C­{1H}, and 77Se­{1H} NMR spectra were found to be characteristic. The single crystal structures of 14 have been established by X-ray crystallography. The complexes 14 have been found efficient for catalytic transfer hydrogenation (TH) of aldehydes and ketones in glycerol, which acts as a solvent and hydrogen source. Complexes 12 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.

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