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(mu-PyBPT-kappa N-3,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 using4-(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(mu-4-MePyBPT-kappa N-3, CS)(CO)(2)](2) (2) and [Ru(mu-6-MePyBPT-kappa(3) N,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(eta(6)-C6H6)(PyDBT-kappa N-2,S)Cl]CF3SO3 (4). Complex 1 contains C-i and C-2 symmetrical isomers, 1a and 1b, respectively, which were separated. The latter isomerized to 1a in DMSO-d(6) at 80 degrees C. The stepwise formation of the same NCS pincer ligand was established in the reaction of [Rh(mu-Cl)(CO)(2)](2) with PyDBT. The facile reaction at room temperature produced the mononuclear rhodium(I) complex cis-[RhCI(CO)(2)(eta(1)-N-PyDBT)] (5). The isolated complex 5 was converted to the tetranuclear rhodium(I/III/III/I) complex [{Rh(mu-PyBPT-kappa(3) N,C,S)}(mu-Cl)(2) {Rh(CO)(2)}](2)(6)at 100 degrees C for 3 days.