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

The dimers [{(eta(n)-ring)MCl}(2)(mu-Cl)(2)] ((eta(n)-ring)M = (eta(5)-C5Me5)Ir, (eta(6)-p-MeC(6)H(4)iPr) Ru) react with the modified cysteines S-benzyl-(L)-cysteine (HL1) or S-benzyl-alpha-methyl-(L)-cysteine (HL2) affording cationic complexes of the formula [(eta(n)-ring)MCl(kappa N-2,S-HL)]Cl (1, 2) in good yield. Addition of NaHCO3 to complexes 1 and 2 gave equilibrium mixtures of neutral [(eta(n)-ring)MCl(kappa N-2,O-L)] (3, 4) and cationic [(eta(n)-ring)M(kappa N-2,O,S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO3 to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-L-cysteine (HL3) and NaHCO3 to the dimers [{(eta(n)-ring)MCl}(2)(mu-Cl)(2)] affords the neutral compounds [(eta(n)-ring)MCl(kappa O-2,S-L3)] ((eta(n)-ring)M = (eta(5)-C5Me5)Ir (5a), (eta(6)-p-MeC(6)H(4)iPr)Ru (5b)). Complexes of the formula [(eta(n)-ring)MCl(kappa N-3,O,S-L)][SbF6] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF6 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 NaHCO3 affording the neutral complexes [(eta(n)-ring)M(kappa N-3,O,S-L3(-H))] ((eta(n)-ring)M = (eta(5)-C5Me5)Ir (9a), (eta(6)-p-MeC(6)H(4)iPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers [{(eta(n)-ring)MCl}(2)(mu-Cl)(2)] with HL3 and two equivalents of NaHCO3. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (R-Ir,R-C,R-S)-[(eta(C5Me5)-C-5)Ir(kappa N-3,O,S-L1)][SbF6] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound [(eta(5)-C5Me5)Ir(kappa N-3,O,S-L3(-H))] (9a) undergoes have been determined through variable temperature H-1 NMR studies.