Ruthenium and Rhodium Complexes with Thiolate-Containing Pincer Ligands Produced by C−S Bond Cleavage of Pyridyl-Substituted Dibenzothiophenes

Treatment of 4-(2′-pyridyl)dibenzothiophene (PyDBT) with the ruthenium carbonyl cluster [Ru3(CO)12] gave the diruthenium(II) complex [Ru(μ-PyBPT-κ3N,C,S)(CO)2]2 (1), where PyBPT denotes a dianion of 3′-(2′′-pyridyl)-1,1′-biphenyl-2-thiol. The tridentate-N,C,S PyBPT ligand provides a pincer structure consisting of a six-membered thiaruthenacycle and a five-membered azaruthenacycle. The thiolate-containing NCS pincer ligand in 1 is produced by cleavage of a carbon−sulfur bond adjacent to a pyridyl group in PyDBT. The corresponding reactions using 4-(4′-methyl-2′-pyridyl)dibenzothiophene (4-MePyDBT) and 4-(6′-methyl-2′-pyridyl)dibenzothiophene (6-MePyDBT) afforded the diruthenium(II) complexes with the same pincer framework [Ru(μ-4-MePyBPT-κ3N,C,S)(CO)2]2 (2) and [Ru(μ-6-MePyBPT-κ3N,C,S)(CO)2]2 (3), respectively. The much slower formation of 3 certifies the reaction path through the initial coordination of the pyridyl group to Ru or the formation of an N,S-chelate structure. Indeed, PyDBT showed the chelating ability in the ruthenium(II) complex [Ru(η6-C6H6)(PyDBT-κ2N,S)Cl]CF3SO3 (4). Complex 1 contains Ci and C2 symmetrical isomers, 1a and 1b, respectively, which were separated. The latter isomerized to 1a in DMSO-d6 at 80 °C. The stepwise formation of the same NCS pincer ligand was established in the reaction of [Rh(μ-Cl)(CO)2]2 with PyDBT. The facile reaction at room temperature produced the mononuclear rhodium(I) complex cis-[RhCl(CO)2(η1-N-PyDBT)] (5). The isolated complex 5 was converted to the tetranuclear rhodium(I/III/III/I) complex [{Rh(μ-PyBPT-κ3N,C,S)}(μ-Cl)2{Rh(CO)2}]2 (6) at 100 °C for 3 days.