Syntheses, structures and immobilization of ruthenium complexes bearing N,O-Schiff-base or N,N′-diamine ligands functionalized with alkoxysilyl groups

Abstract

Condensation of γ-aminopropyltriethoxysilane and substituted salicylaldehydes in ethanol afforded three new Schiff-base compounds [(EtO)3Si(CH2)3N=CHArOH] (Ar = C6H4, L1H; C6H3(4-Cl), L2H; C6H2(2,4-tBu2), L3H). Treatment of [Ru(NO)Cl3⋅xH2O] with L1H in the presence of Et3N in THF gave a ruthenium nitrosyl complex [RuCl2(NO)(κ2-O,N-L1)(OEt2)] (1) with a linear N≡O moiety. Reactions of [(η6-p-cymene)RuCl(μ-Cl)]2 with L1H or L2H in the presence of AgNO3 and Et3N afforded complexes [(η6-p-cymene)RuCl(κ2-O,N-L)] (L = L1, 2; L2, 3). While reaction of [Ru(CO)2Cl2]n and L3H in the presence of Et3N afforded an anionic ruthenium complex (Et3NH)[RuCl2(CO)2(κ2-O,N-L3)] (4). Treatment of alkoxysilyl functionalized N,N′-diamine compound N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine (L4) with [Ru(PPh3)3Cl2] or [Ru(DMSO)4Cl2] (DMSO = dimethyl sulfoxide) or [Ru(COD)Cl2]x (COD = 1,5-cyclooctadiene) led to formation of complexes [Ru(PPh3)2Cl2(κ2N-L4)] (5), [Ru(DMSO)2Cl2(κ2N-L4)] (6), and [Ru(COD)Cl2(κ2N-L4)] (7), respectively. Complexes 1–7 were characterized by microanalyses, IR and NMR spectroscopies, and their structures were also confirmed by single-crystal X-ray diffraction. Immobilization of complexes 2 and 5 on SBA-15, and characterization of these hybrid heterogeneous catalysts were studied by transmission electron microscopy (TEM), IR and low pressure N2 adsorption/desorption measurement. The heterogeneous catalysts were also briefly tested for oxidation of benzyl alcohol to benzaldehyde.