Amido-hydrido Complexes of Ruthenium and Osmium PDF Download

Author: Sean Clapham
Publisher:
ISBN: 9780494397831
Category :
Languages : en
Pages : 404

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Book Description
The new air-sensitive ruthenium and osmium amido-hydrido complexes RuH(NHCMe 2CMe2NH2)(PPh3)2 and OsH(NHCMe 2CMe2NH2)(PPh3)2 have been synthesized and characterized. The hydrogenation of ketones to alcohols using these catalysts was explored. This included exploring the reactivity of these complexes toward hydrogen gas, ketones and alcohols, as well as performing kinetic experiments. The behaviour of the ruthenium and osmium systems were compared and mechanisms were proposed. Density functional calculations were carried out to model the proposed mechanisms and these were compared with experimental results. RuH(NHCMe2CMe2NH2)(PPh 3)2 was reacted with formic acid to generate RuH(OCHO)(NH 2CMe2CMe2NH2)(PPh3) 2, a model compound for the transfer of hydrogen from ruthenium to a ketone. The reactivity of the amido complexes towards weakly acidic compounds, HX, to generate new diamino complexes of the type MHX(NH2CMe 2CMe2NH2)(PPh3)2 (M = Ru or Os, X = H, OPh, NCCHCN, CH(COOMe)2, CCPh, OPPh2, OP(OEt)2, p-SC6H4OMe) was explored. Useful correlations were drawn relating the effect that the ligand trans to hydride has on the NMR and infrared spectra of these compounds. The complex RuH(OPh)(NH 2CMe2CMe2NH2)(PPh3) 2 hydrogen bonds with an equivalent of phenol to generate RuH(OPh···HOPh)(NH 2CMe2CMe2NH2)(PPh3) 2, which contains an interesting 6-membered ring as a result. This structure is similar to the proposed transition state for the alcohol-assisted splitting of dihydrogen by OsH(NHCMe2CMe2NH2)(PPh 3)2. The novel ruthenium complexes RuHX(1,2-NH2C 6H10NH2)(PPh3)2 (X = OPh, NCCHCN, CCPh, OPPh2, OP(OEt)2, p-SC6H 4OMe) were generated from the reaction of RuHCl(1,2-NH2C 6H10NH2)(PPh3)2 with HX and base. The complexes RuH(CCPh)(diamine)(PPh3)2 (diamine = NH2CMe2CMe2NH2 or 1,2-NH 2C6H10NH2) catalyze the hydrogenation of acetophenone to 1-phenylethanol, but less efficiently than the amido complexes. The complexes MH(CH(COOMe)2)(NH2CMe2CMe 2NH2)(PPh3)2 (M = Ru or Os) and the amido complexes also catalyze the Michael addition of dimethylmalonate to 2-cyclohexen-1-one. The reaction of RuH(NCCHCN)(NH2CMe2CMe 2NH2)(PPh3)2 with 2-cyclohexen-1-one leads to the formation of the trapped Michael adduct RuH(NCC(C6H 9O)CN)(NH2CMe2CMe2NH2)(PPh 3)2. The structure of this complex was used in proposing a mechanism for Michael addition reactions catalyzed by the amido complexes. The relative reactivity and strength of the osmium and ruthenium amido bonds were investigated through a series of competition experiments where HX (X = Cl, OPh, NCCHCN, p-SC6H4OMe) was transferred from OsHX(NH2CMe2CMe2NH2)(PPh 3)2 to RuH(NHCMe2CMe2NH2)(PPh 3)2 leading to RuHX(NH2CMe2CMe 2NH2)(PPh3)2 and OsH(NHCMe2CMe 2NH2)(PPh3)2.