Search

A series of iridium and rhodium complexes M(COD)((PNP)-P-Ph-P-H)]Cl {M = Ir (1), Rh (2)}, MH2Cl((PNP)-P-Ph-P-H)] {M = Ir (3), Rh (4)} and IrH3((PNP)-P-Ph-P-H)] (6) supported by pincer ligand HeN(CH2CH2PPh2)(2) {(PNP)-P-Ph-P-H} have been synthesized and characterized. All complexes were isolated in good yields. The iridium trihydride complex IrH3((PNP)-P-Ph-P-H)] (6) was found to be an active catalyst for the hydrogenation of CO2 in 1 M aqueous KOH solution. It also acts as a catalyst for the base-free hydrogenation of carbonyl and imine substrates in MeOH. Under similar hydrogenation conditions, 2-cyclohexen-1-one undergoes solvent assisted tandem Michael addition-reduction mediated by bifunctional Lewis-acid-catalyst IrH3((PNP)-P-Ph-P-H)] in ROH (R = Me, Et) at room temperature. The complexes 1, 3, 4, and 6 were characterized by X-ray crystallography. Extensive hydrogen bonding interactions N-H center dot center dot center dot H-Ir (2.15 angstrom), N-H center dot center dot center dot center dot Cl (2.370 angstrom) were noted in the crystal structures of these complexes. (C) 2018 Elsevier B.V. All rights reserved.

A series of new homobimetallic hydride complexes of ruthenium bearing N-heterocyclic carbene ligand of the type [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4,4’-bpy = 4,4’-bipyridine) (2), [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyen)] (4,4’-dpyen = 1,2-bis(4-pyridyl)ethylene) (4), and [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyan)] (4,4’-dpyan = 1,2-bis(4-pyridyl)ethane) (5) has been synthesized and characterized starting from [RuHCl(IMes)(PPh3)(CO)] (1). The pyridyl-based ligands, (4,4’-bpy), (4,4’-dpyen), and (4,4’-dpyan) in these complexes act as the bridging ligands between the two ruthenium fragments. The bridging ligand in these bimetallic complexes is very labile. Reaction of these complexes with PMe3 led to extensive substitution of not only the bridging ligand but also the PPh3 ligands. Reaction of complexes 2, 4, and 5 with HOTf at low temperatures result in the formation of the corresponding dihydrogen complexes, [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-bpy)][OTf]2 (9), [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyen)][OTf]2 (10), and [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyan)][OTf]2 (11), respectively. These are the first examples of homobimetallic ruthenium dihydrogen complexes bearing NHC ligands. The intact nature of the H–H bond in these derivatives was established by variable temperature 1H (400 MHz) spin-lattice relaxation time (T1, ms) measurements and from the H, D coupling constants of the corresponding HD isotopomers. The H–H distances (dHH) in these complexes fall in the range 0.95–0.98 A. Hydrogen evolution takes place upon warming the dihydrogen complexes generated at low temperatures, indicating the labile nature of the H2 ligand in these complexes. The X-ray crystal structure of [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] complex (2) has been determined.

Ruthenium pincer complex RuHCl(PPh3)(PNP)] (PNP = Me-N(CH2CH2PPh2)(2)) (1) was synthesized by reaction of RuHCl(PPh3)(3) with Me-N(CH2CH2PPh2)(2) and characterized. Abstraction of chloride ligand in complex 1 using NaBA(4)(f) in the presence of small molecules such as N-2, H-2, O-2, and CO resulted in the formation of trans-RuH(L)(PPh3)(PNP)]BAr4f {L = N-2 (2), H-2 (4), O-2 (5), CO (6)} complexes. Complexes 2, 4, 5, and 6 have been characterized by various techniques. The reaction of RuHCl(PPh3)(PNP)] complex with NaBH4 gave a borohydrido complex RuH(eta(1)-BH4)(PPh3)(PNP)] (7) which upon reaction with NEt3 generates a mixture of cis and trans dihydrides RuH2(PPh3)(PNP)] (8). The reaction of dihydride complexes with CO2 leads to the formation of formate complex RuH(eta(1)-HCO2)(PPh3)(PNP)] (9). In addition, dihydrogen complexes Ru(eta(2)-H-2)(L)(PPh3)(PNP)](n+) (L = Cl (10), CO (11)) having different trans donor ligands were synthesized by protonation of trans-RuH(L)(PPh3)(PNP)](n+) {n = 0, L = CI; n = 1, L = CO} complexes with HOTf at low temperature. Complexes I and 6 have been characterized by X-ray crystallography. (C) 2016 Elsevier B.V. All rights reserved.

Two new Ru(II)-complexes [RuH(Tpms)(PPh3)2] 1 (Tpms = (C3H3N2)3CSO3, tris-(pyrazolyl)methane sulfonate) and [Ru(OTf)(Tpms)(PPh3)2] 2 (OTf = CF3SO3) have been synthesized and characterized wherein Ru–H and Ru–OTf are the key reactive centers. Reaction of 1 with HOTf results in the [Ru(η2-H2)(Tpms)(PPh3)2][OTf] complex 3, whereas reaction of 1 with Me3SiOTf affords the dihydrogen complex 3 and complex 1 through an unobserved σ–silane intermediate. In addition, an attempt to characterize the sigma methane complex via reaction of complex 1 with CH3OTf yields complex 2 and free methane. On the other hand, reaction of [Ru(OTf)(Tpms)(PPh3)2] 2 with H2 and PhMe2SiH at low temperature resulted in σ–H2, 3 and a probable σ–silane complexes, respectively. However, no σ–methane complex was observed for the reaction of complex 2 with methane even at low temperature.