Half-sandwich complexes of iridium and ruthenium containing cysteine-derived ligands

Abstract

The dimers [{(η-ring)MCl}(μ-Cl)] ((η-ring)M = (η-CMe)Ir, (η-p-MeCHiPr)Ru) react with the modified cysteines S-benzyl-l-cysteine (HL1) or S-benzyl-α-methyl-l-cysteine (HL2) affording cationic complexes of the formula [(η-ring)MCl(κN,S-HL)]Cl (1, 2) in good yield. Addition of NaHCO to complexes 1 and 2 gave equilibrium mixtures of neutral [(η-ring)MCl(κN,O-L)] (3, 4) and cationic [(η-ring)M(κN,O,S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-l-cysteine (HL3) and NaHCO to the dimers [{(η-ring)MCl}(μ-Cl)] affords the neutral compounds [(η-ring)MCl(κO,S-L3)] ((η-ring)M = (η-CMe)Ir (5a), (η-p-MeCHiPr)Ru (5b)). Complexes of the formula [(η-ring)MCl(κN,O,S-L)][SbF] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF to the solutions of compounds 5 or to the mixtures of complexes 3/6Cl and 4/7Cl. The amide proton of compounds 8aSb and 8bSb can be removed by addition of NaHCO affording the neutral complexes [(η-ring)M(κN,O,S-L3)] ((η-ring)M = (η-CMe)Ir (9a), (η-p-MeCHiPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers [{(η-ring)MCl}(μ-Cl)] with HL3 and two equivalents of NaHCO. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (R,R,R)-[(η-CMe)Ir(κN,O,S-L1)][SbF] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound [(η-CMe)Ir(κN,O,S-L3)] (9a) undergoes have been determined through variable temperature H NMR studies.