title: POP-pincer ruthenium complexes: d(6) counterparts of osmium d(4) species.
abstract: A wide range of ruthenium complexes stabilized by the POP-pincer ligand xant(P(i)Pr2)2 (9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) were prepared starting from cis-RuCl2{κ-S-(DMSO)4} (1; DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this adduct with the diphosphine under reflux leads to RuCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (2), which reacts with H2 in the presence of a Brønsted base. The reaction in the presence of Et3N affords RuHCl{xant(P(i)Pr2)2}(κ-S-DMSO) (3), whereas NaH removes both chloride ligands to give RuH2{xant(P(i)Pr2)2}(κ-S-DMSO) (4). The stirring of 3 in 2-propanol under 3 atm of H2 for a long time produces the elimination of DMSO and the coordination of H2 to yield the dihydrogen derivative, RuHCl(η(2)-H2){xant(P(i)Pr2)2} (5). In contrast to H2, PPh3 easily displaces DMSO from the metal center of 3 to afford RuHCl{xant(P(i)Pr2)2}(PPh3) (6), which can be also obtained starting from RuHCl(PPh3)3 (7) and xant(P(i)Pr2)2. In contrast to 3, complex 4 does not undergo DMSO elimination to give RuH2(η(2)-H2){xant(P(i)Pr2)2} (8) under a H2 atmosphere. However, the latter can be prepared by hydrogenation of Ru(COD)(COT) (9; COD = 1,5-cyclooctadiene and COT = 1,3,5-cyclooctatriene) in the presence of xant(P(i)Pr2)2. A more efficient procedure to obtain 8 involves the sequential hydrogenation with ammonia borane of the allenylidene derivative RuCl2(═C═C═CPh2){xant(P(i)Pr2)2} (10), which is formed from the reaction of 2 with 1,1-diphenyl-2-propyn-1-ol. The hydrogenation initially gives RuCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (11), which undergoes the subsequent reduction of the Ru-C double bond to yield the hydride-tetrahydroborate complex, RuH(η(2)-H2BH2){xant(P(i)Pr2)2} (12). The osmium complex, OsCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (13), reacts with 1,1-diphenyl-2-propyn-1-ol in a similar manner to its ruthenium counterpart 2 to yield the allenylidene derivative, OsCl2(═C═C═CPh2){xant(P(i)Pr2)2} (14). Ammonia borane also reduces the Cβ-Cγ double bond of the allenylidene of 14. However, the resulting vinylidene species, OsCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (15), is inert. Complex 12 is an efficient catalyst precursor for the hydrogen transfer from 2-propanol to ketones, the α-alkylations of phenylacetonitrile and acetophenone with alcohols, and the regio- and stereoselective head-to-head (Z) dimerization of terminal alkynes.
authors.affiliation: Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Joaquín
authors.initials: J
authors.lastname: Alós
authors.forename: Tamara
authors.initials: T
authors.lastname: Bolaño
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Esteruelas
authors.forename: Montserrat
authors.initials: M
authors.lastname: Oliván
authors.forename: Enrique
authors.initials: E
authors.lastname: Oñate
authors.forename: Marta
authors.initials: M
authors.lastname: Valencia