Spectroscopic, structural and theoretical investigation of alkenyl ruthenium complexes supported by sulfur-nitrogen mixed-donor ligands

A series of molecules bearing both sulfur and nitrogen donors has been investigated as ligands for sigma-alkenyl ruthenium complexes. On deprotonation, the ligands, 4-amino-2-mercaptopyrimidine (HL1), 2-amino-5-mercapto-1,3,4-thiadiazole (HL2), 2-mercaptothiazoline (HL3), 4-hydroxy-2-mercaptopyrimidine (HL4) and 2-mercaptoquinoline (HL5) all react with alkenyl complexes of the form [RuRCl(CO)(BTD)(PPh3)(2)] [R = CH=CHC6H5, CH=CHC6H4Me-4, C(C CPh)= CHPh; BTD = 2,1,3-benzothiadiazole] through loss of chloride and BTD ligands to yield [RuR(L)(CO)(PPh3)(2)]. Four of these ligands have alternative potential coordination modes and donor groups. In all cases complexation occurs to form four-membered nitrogen-sulfur chelates with the pendant amino or hydroxy functionality playing no role in coordination. In the case of the 4-aminopyrimidine-2-thiolate (L-1) ligand, this was confirmed by a single-crystal X-ray study. 2-Mercaptothiazoline (L-3) has the ability to coordinate through two sulfur donors, however, chelation to nitrogen and sulfur donors is preferred as demonstrated by a structural study. This observation is supported by theoretical calculations, which show that a complex displaying the nitrogen-sulfur chelate is of significantly lower energy than one bonded to the ligand through two sulfur donors, despite lone pairs being available in both cases. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).