A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine–phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1–4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)2I2(P∩S)] (1a) {P∩S = η2-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)2I2(P∼S)] (1b–d) {P∼S = η1-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)2I2]n with equimolar quantity of the ligands Ph2P(CH2)nP(S)Ph2 {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)2I2(P∼S)2] (2a–d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028–2103 cm−1. The ν(PS) band of complex 1a occurs 23 cm−1 lower region compared to the corresponding free ligand suggesting chelation via metal–sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, 1H, 13C and 31P NMR spectroscopy.