Half Sandwich Complexes of Chalcogenated Pyridine Based bi-(N, S/Se) and Terdentate (N, S/Se, N) Lig

Dalton Trans. 2013, 42, 8736-8747

The half sandwich complexes [(η6-C6H6)Ru(L)Cl][PF6] (1–5) have been synthesized by the reactions of (2-arylchalcogenomethyl)pyridine [L = L1–L3] and bis(2-pyridylmethyl)chalcogenide [L = L4–L5] (chalcogen = S, Se; Ar = Ph/2-pyridyl for S, Ph for Se) with [(η6-C6H6)RuCl2]2, at room temperature followed by treatment with NH4PF6. Their HR-MS, 1H, 13C{1H} and 77Se{1H} NMR spectra have been found characteristic. The single crystal structures of 1–5 have been established by X-ray crystallography. The Ru has pseudo-octahedral half sandwich “piano-stool” geometry. The complexes 1–5 have been found efficient for catalytic oxidation of alcohols with N-methyl morpholine-N-oxide (NMO) and transfer hydrogenation of ketones with 2-propanol (at moderate temperature 80 °C) as TON values are up to 9.9 × 103 and 9.8 × 103 respectively for the two catalytic reactions. On comparing the required catalyst loading for good conversions and reaction time for the present complexes with those reported in literature for other transfer hydrogenation/oxidation catalysts, it becomes apparent that 1–5 have good promise. The complexes of Se ligands have been found more efficient than their sulphur analogues. The complexes of bidentate ligands are more efficient than those of terdentate, due to difficult bond cleavage in the case of latter. These orders of efficiency are supported by DFT calculations. The calculated bond lengths/angles by DFT are generally consistent with the experimental ones.