Cyanosilylation of carbonyl compounds catalyzed by half-sandwich (η6-p-cymene) Ruthenium(II) complexes bearing heterocyclic hydrazone derivatives

Abstract

A new class of half-sandwich (ƞ6-p-cymene) ruthenium(II) complexes supported by heterocyclic hydrazone derivatives of general formula [Ru(ƞ6-p-cymene)(Cl)(L)] where L represents N’-((1H-pyrrol-2-yl)methylene)furan-2-carbohydrazide (L1), N’-((1H-pyrrol-2-yl)methylene)thiophene-2-carbohydrazide (L2) or N’-((1H-pyrrol-2-yl)methylene)isonicotinohydrazide (L3) were synthesized. Both ligand precursors and complexes were characterized by elemental and spectral analysis (IR, UV–Vis, NMR and mass spectrometry). The molecular structures of all Ru complexes [Ru(ƞ6-p-cymene)(Cl)(L)] were determined by single-crystal X-ray diffraction as three-legged piano-stool. The Ru(II) complexes were used as catalysts for the cyanosilylation of aldehydes (aliphatic, aromatic, α,β-unsaturated and heterocyclic aldehydes) with trimethylsilyl cyanide (TMSCN). All reactions were performed at room temperature and catalytic conditions as solvents, catalyst and catalyst loading were experimentally optimized. Using 0.5 mol% of Ru catalyst 3 in Et2O it was possible to prepare cyanosilylethers in good-to-excellent isolated yields.