Thermodynamic Studies of [H_(2)Rh(diphosphine)_2]^+ and [HRh(diphosphine)_(2)(CH_(3)CN)]^(2+) Complexes in Acetonitrile

Thermodynamic studies of a series of [H_(2)Rh(PP)_2]^+ and [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes have been carried out in acetonitrile. Seven different diphosphine (PP) ligands were selected to allow variation of the electronic properties of the ligand substituents, the cone angles, and the natural bite angles (NBAs). Oxidative addition of H_2 to [Rh(PP)_2]^+ complexes is favored by diphosphine ligands with large NBAs, small cone angles, and electron donating substituents, with the NBA being the dominant factor. Large pK_a values for [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes are favored by small ligand cone angles, small NBAs, and electron donating substituents with the cone angles playing a major role. The hydride donor abilities of [H_(2)Rh(PP)_2]^+ complexes increase as the NBAs decrease, the cone angles decrease, and the electron donor abilities of the substituents increase. These results indicate that if solvent coordination is involved in hydride transfer or proton transfer reactions, the observed trends can be understood in terms of a combination of two different steric effects, NBAs and cone angles, and electron-donor effects of the ligand substituents

A new xantphos-type ligand and its gold(I) complexes: Synthesis, structure, luminescence

A novel xantphos analog diphosphine ligand, 9,9-dimethyl-4,5-bis(diphenylphosphinomethyl)-9H-xanthene (X(CP)2), with methylene groups inserted between the xanthene skeleton and the two diphenylphosphine units, has been synthesized. A two-coordinate and a three-coordinate gold(I) complex of the ligand, [Au2Cl2(X(CP)2)] and [AuCl(X(CP)2)], have been prepared and studied by X-ray diffraction, NMR and optical spectroscopy. In the solid state, [AuCl(X(CP)2)] adopts a highly ordered structure with a planar xanthene skeleton that faces another plane composed of two phenyl rings and the AuCl moiety. The structure of [Au2Cl2(X(CP)2)] is much less regular, the two P–Au–Cl vectors point to the opposite sides of the folded xanthene backbone. The exchange-broadened resonances in the NMR spectra of [AuCl(X(CP)2))] indicate that this complex exists as a mixture of various chemical species and/or conformers in solution. In contrast, the NMR spectra of [Au2Cl2(X(CP)2)] exclude any medium-range exchange processes. Aurophilic interactions are absent in both X(CP)2 complexes. X(CP)2, as well as its two gold complexes, is phosphorescent in the solid state; the complexes emit at higher wavelengths and with longer lifetimes than the free ligand

P–C and C–H Bond Cleavages of dppm in the Thermal Reaction of [Ru\u3csub\u3e3\u3c/sub\u3e(CO)\u3csub\u3e10\u3c/sub\u3e(μ-dppm)] with Benzothiophene: X-ray structures of [Ru\u3csub\u3e6\u3c/sub\u3e(μ-CO)(CO)\u3csub\u3e13\u3c/sub\u3e{μ\u3csub\u3e4\u3c/sub\u3e-PhP(C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3e)PPh}(μ\u3csub\u3e6\u3c/sub\u3e-C)] and [Ru\u3csub\u3e4\u3c/sub\u3e(CO)\u3csub\u3e9\u3c/sub\u3e(μ\u3csub\u3e3\u3c/sub\u3e-η\u3csup\u3e2\u3c/sup\u3e-PhPCH\u3csub\u3e2\u3c/sub\u3ePPh\u3csub\u3e2\u3c/sub\u3e)(μ\u3csub\u3e4\u3c/sub\u3e-η\u3csup\u3e6\u3c/sup\u3e:η\u3csup\u3e1\u3c/sup\u3e:η\u3csup\u3e1\u3c/sup\u3e-C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3e)(μ-H)]

The thermal reaction of [Ru3(CO)10(μ-dppm)] (1) with benzothiophene in refluxing toluene gives a complex mixture of products. These include the known compounds [Ru2(CO)6{μ-CH2PPh(C6H4)PPh}] (2), [Ru2(CO)6{μ-C6H4PPh(CH2)PPh}] (3), [Ru3(CO)9{μ3-η3-(Ph)PCH2P(Ph)C6H4}] (4) and [Ru3(CO)10{μ-η2-PPh(CH2)(C6H4)PPh}] (6), as well as the new clusters [Ru6(μ-CO)(CO)13{μ3-η2-PhP(C6H4)PPh}(μ6-C)] (5) and [Ru4(CO)9(μ3-η2-PhPCH2PPh2)(μ4-η6:η1:η1-C6H4)(μ-H)] (7). The solid-state molecular structures of 5 and 7 were confirmed by single crystal X-ray analyses. Compound 5 consists of interesting example of a hexaruthenium interstitial carbido cluster having a tetradentate diphosphine ligand derived from the activation of P–C and C–H bonds of the dppm ligand in 1. The tetranuclear compound 7 consists of a unique example of a non-planar spiked triangular metal fragment of ruthenium [Ru(1), Ru(2) and Ru(3)] unit with Ru(4) being bonded to Ru(1). The μ4-η1:η6:η1-benzyne ligand in this compound represents a previously uncharacterized bonding mode for benzyne. Compounds 5 and 7 do not contain any benzothiophene-derived ligand. The reaction of 4 with benzothiophene gives 2, 3, 5 and 6. Thermolysis of 1 in refluxing toluene gives 2, 3 and 4; none of 5 and 7 is detected in reaction mixture

Synthesis and C−C Coupling Reactivity of a Dinuclear Ni^I−Ni^I Complex Supported by a Terphenyl Diphosphine

Mono- and bimetallic complexes of nickel supported by a terphenyl diphosphine have been synthesized. The reported complexes show diverse metal−arene interactions in the solid state. Reactions of an o,o′-biphenyldiyl dinickel complex with CO and dichloroalkanes lead to fluorene derivatives, indicating the formation of carbon−carbon bonds at a bimetallic moiety

Spectral, crystallographic, theoretical and antibacterial studies of palladium(II)/platinum(II) complexes with unsymmetric diphosphine ylides

The reaction of alpha-keto-stabilized diphosphine ylides [Ph2P(CH2)(n)PPh2C(H)C(O)C6H4-p-CN] (n = 1 (Y-1); n = 2 (Y-2)) with dibromo(1,5-cyclooctadiene) palladium(II)/platinum(II) complexes, [Pd/PtBr2(cod)], in equimolar ratio gave the new cyclometalated Pd(II) and Pt(II) complexes [Br2Pd(kappa(2)-Y-1)] (1), [Br2Pt(kappa(2)-Y-1)] (2), [Br2Pd(kappa(2)-Y-2)] (3) and [Br2Pt(kappa(2)-Y-2)] (4). These compounds were screened in a search for novel antibacterial agents and characterized successfully using Fourier transfer infrared and NMR (H-1, C-13 and P-31) spectroscopic methods. Also, the structures of complexes 1 and 2 were characterized using X-ray crystallography. The results showed that the P,C-chelated complexes 1 and 2 have structures consisting of five-membered rings, while 3 and 4 have six-membered rings, formed by coordination of the ligand through the phosphine group and the ylidic carbon atom to the metal centre. Also, a theoretical study of the structures of complexes 1-4 was conducted at the BP86/def2-SVP level of theory. The nature of metal-ligand bonds in the complexes was investigated using energy decomposition analyses (EDA) and extended transition state combined with natural orbitals for chemical valence analyses. The results of EDA confirmed that the main portions of Delta E-int, about 57-58%, in the complexes are allocated to Delta E-elstat

Double Carbon−Hydrogen Activation of 2-Vinylpyridine: Synthesis of Tri- and Pentanuclear Clusters Containing the μ-NC\u3csub\u3e5\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3eCH═C Ligand

Reactions of 2-vinylpyridine with the triruthenium complexes [Ru3(CO)12] and [Ru3(CO)10(μ-dppm)] leads to a previously unknown double carbon−hydrogen bond activation of the β-carbon of the vinyl group to afford the pentaruthenium and triruthenium complexes [Ru5(CO)14(μ4-C5H4CH═C)(μ-H)2] (1) and [Ru3Cl(CO)5(μ-CO)(μ-dppm)(μ3-NC5H4CH═C)(μ-H)] (2), respectively. Crystal structures reveal two different forms of bridging of the dimetalated 2-vinylpyridyl ligand, capping a square face in 1 and a triangular face in 2

Asymmetric Hydrogenation of 1-alkyl and 1-aryl vinyl benzoates: a broad scope procedure for the highly enantioselective synthesis of 1-substituted ethyl benzoates

The enantioselective hydrogenation of enol esters of formula CH2=C(OBz)R with rhodium catalysts based on phosphine-phosphite ligands (P-OP) has been studied. The reaction has a broad scope and it is suitable for the preparation of products possessing a wide variety of R substituents. For the cases where R is a primary alkyl high catalyst activity (S/C = 500) and enantioselectivities (95-99 % ee) were obtained with a catalyst characterized by an ethane backbone and a PPh2 fragment. In contrast, for R = tBu a catalyst possessing a benzene backbone provided the best results (97 % ee). Derivatives with a cycloalkyl R substituent were particularly difficult substrates for this reaction. A broader catalyst screening was required for these substrates, which identified a catalyst possessing a P(m-xylyl)2 fragment as the most appropriate one, affording enantioselectivities between 90 and 95 % ee. Outstanding enantioselectivities (99 % ee) and high catalyst activity (S/C = 500-1000) were also obtained in the case of substrates bearing a Ph or a fluoroaryl R substituent. In addition, the system is also appropriate for the preparation of other synthetically useful esters as those for R = benzyl, 2-phenylethyl or Nphthalimido alkyl chains. Likewise, the hydrogenation of divinyl dibenzoates proceeded with very high diastero- and enantioselectivity, generating rather low amounts of the meso isomer (3-6 %). On the other hand, substrates with Br- and MeO- substituents at the phenyl benzoate ring, suitable for further functionalization, have also been examined. The results obtained indicate no detrimental effect of these substituents in the hydrogenation. Alternatively, the methodology has been applied to the highly enantioselective synthesis of deuterium isotopomers of 1-octyl benzoate bearing CDH2, CD2H or CD3 fragments. Finally, as a practical advantage of the present system, it has been observed that the high performance of the catalysts is retained in high concentrated solutions or even in the neat substrate, then minimizing both the amount of solvent added and the volume of the reactionJunta de Andalucía 2009/FQM-4832CSIC 201480E03 1Ministerio de Ciencia e Innovación CTQ2010- 14796/BQ

Energy Conversion and Utilization Technologies Program (ECUT) electrocatalysis research

The general field of electrocatalysis, from both the technical and business standpoints is accessed and research areas and approaches most likely to lead to substantial energy/cost savings are identified. The overall approach was to compile and evaluate available information, relying heavily on inputs/recommendations of research managers and technical personnel in responsible positions in industry and at universities. Some promising approaches identified to date include the use of transition metal compounds as electrocatalysts and the use of the new electrochemical photocapacitance spectroscopy (EPS) technique for electrocatalyst characterization/development. For the first time, an oxygen electrocatalyst based on the K2NiF4 structure was synthesized, investigated and compared with a perovskite analog. Results show that this class of materials, based on Ni(3+), forms very efficient and stable O2 anodes in basic solution and suggest that other structure-types be examined in this regard. The very difficult problem of dinitrogen and carbon dioxide electroreductions is addressed through the use of biological model systems which can mimic the enzyme processes in nature