Synthesis, characterization and crystal structures of half-sandwich ruthenium complexes with bidentate chiral Schiff-base ligands

Abstract

Condensation of salicylaldehyde or 5-nitrosalicylaldehyde with (S)-(+)-2-amino-3-methyl-1-butanol in refluxing ethanol afforded the chiral Schiff-base ligands (S)-N-(1-hydroxymethylisobutyl)salicylidene (HL1*) and (S)-N-1-hydroxymethylisobutyl-5-nitrosalicylidene (HL2*), respectively. Similarly, reaction of 3,5-di-tert-butylsalicylaldehyde or 3,5-dibromosalicylaldehyde with (R)-(+)-α-methylbenzylamine gave the chiral Schiff base ligands (R)-N-(1-phenylethyl)-3,5-di-tert-butylsalicylidene (HL3*) and (R)-N-(1-phenylethyl)-3,5-dibromosalicylidene (HL4*), respectively. Treatment of 3,5-dibromosalicylaldehyde with (S)-(+)-2-amino-1-propanol, (S)-(+)-2-amino-3-methyl-1-butanol or (S)-(−)-2-amino-3-phenyl-1-propanol in refluxing ethanol afforded (S)-N-(1-hydroxymethylethyl)-3,5-dibromosalicylidene (HL5*), (S)-N-(1-hydroxymethylisobutyl)-3,5-dibromosalicylidene (HL6*), and (S)-N-(1-hydroxymethylphenylethyl)-3,5-dibromosalicylidene (HL7*), respectively. Interaction of [(η6-p-cymene)RuCl2]2 with two euivalents of the chiral Schiff-bases HL1*‒HL7* gave the corresponding half-sandwich ruthenium(II) complexes [(η6-p-cymene)Ru(κ2-N,O-L*)Cl] (1–7). The molecular structures of HL1*‒HL7* and the complex 3 have been determined by single-crystal X-ray crystallography.