Search

A manganese catalyst of a facially coordinating P,N,N ligand catalyses the hydrogenation of imines derived from indanone derivatives with high enantioselectivity. There is no requirement for an activating group and imines can be generated in situ. The selectivity can be rationalised by DFT calculations. [ABSTRACT FROM AUTHOR]

Manganese catalysed ester reduction using ethanol as a hydrogen transfer agent in place of dihydrogen is reported. High yields can be achieved for a range of substrates using 1 mol% of a Mn(I) catalyst, with an alkoxide promoter. The catalyst is derived from a tridentate P,N,N ligand. [ABSTRACT FROM AUTHOR]

High diastereoselectivity was observed in the Rh-catalysed reductive amination of 3-arylcyclohexanones to form tertiary amines. This was incorporated into a one-pot enantioselective conjugate addition and diastereoselective reductive amination, including an example of assisted tandem catalysis. [ABSTRACT FROM AUTHOR]

A porous scandium MOF denoted STA-27 (St Andrews Porous Material-27) has been synthesised solvothermally using the 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine anion (TCPP4−) as the tetratopic carboxylate linker. STA-27 possesses a unique scandium-based 1D rod secondary building unit (SBU) comprising corner-sharing scandium Sc2O11 dimers connected via carboxylate groups from the linker. After activation under mild conditions STA-27 is an active Lewis acidic catalyst, while heating at elevated temperatures results in rupturing of the Sc–O–Sc linkages and a phase transition to a different topological type. Under similar synthesis conditions the smaller Al3+ and Ga3+ cations give isostructural MOFs with a different, previously reported, topology type based on chains of corner-sharing MO4(OH)2 octahedra: the Al-form possesses attractive properties for CO2 adsorption. [ABSTRACT FROM AUTHOR]

As part of a programme aimed at exploiting lignin as a chemical feedstock for less oxygenated fine chemicals, several catalytic C-C bond forming reactions utilising guaiacol imidazole sulfonate are demonstrated. These include the cross-coupling of a Grignard, a non-toxic cyanide source, a benzoxazole, and nitromethane. A modified Meyers reaction is used to accomplish a second constructive deoxygenation on a benzoxazole functionalised anisole. [ABSTRACT FROM AUTHOR]

Using the phospholane-phosphite ligand, BOBPHOS, almost perfect regioselectivities and high enantioselectivities (up to 92% ee) are observed in Rh catalysed enantioselective hydroformylation of vinyl arenes. This can be achieved under solvent-free conditions. [ABSTRACT FROM AUTHOR]

Ir complexes of chiral phosphine-diamine ligands catalyse the hydrogenation and transfer hydrogenation of aryl-piperidin-4-yl methanones, and ketones bearing both an aryl group and secondary alkyl substituent with up to 98% e.e., and with substrate to catalyst ratios of up to 4000. [ABSTRACT FROM AUTHOR]

Using a family of novel mononuclear and dinuclear palladium complexes of phanephos ligands, the simultaneous control of regioselectivity and enantioselectivity in the hydroxycarbonylation and alkoxycarbonylation of styrene derivatives has been realised for the first time. [ABSTRACT FROM AUTHOR]

An improved protocol where a pre-cursor, [Ru(Cl)(2)(NBD)(Py)(2)], is treated with ligands to form [RuCl(2)(bidentate ligand)(diamine)] pre-catalysts for ester hydrogenation is reported. This family of catalysts, as well as a range of ruthenium complexes of tridentate P^N^X (X = NR(2), OH) ligands have been investigated in the hydrogenation of aromatic esters. A range of aromatic esters can be hydrogenated in high yields at temperatures between 30 °C and 100 °C.

Phosphine modified rhodium complexes are currently the topic of considerable research as methanol carbonylation catalysts, but often suffer from poor stability. This paper reports on an investigation into how coordination mode affects the elimination of phosphonium salts from rhodium complexes, namely [trans-RhCl(CO)(PPh3)2] 1, [RhCl(CO)(dppe)] 2, [RhCl(CO)(dppb)]2 3, [Rh(TRIPHOS)(CO)2]Cl 4. These complexes are all potential pre-catalysts for methanol carbonylation. The reaction of these complexes with methyl iodide at 140 degrees C under both N2 and CO atmospheres has been studied and has revealed clear differences in the stability of the corresponding Rh(III) complexes. In contrast to both monomeric 2 and dimeric 3 that react cleanly with CH3I to give stable Rh(III) acetyl complexes, 4 forms a novel bidentate complex after the elimination of the one arm of the ligand as a quaternised phosphonium salt. The structure of this complex has been determined spectroscopically and using X-ray crystallography. The mechanism of formation of this novel complex has been investigated using 13CH3I and strong evidence that supports a dissociative mechanism as the means of phosphine loss from the rhodium centre is provided.

Some new bulky fluorinated diphosphines have been prepared and converted to palladium dichloride complexes that have been found to give increased regioselectivity and activity over other Pd-diphosphine systems when used as catalysts for hydroxycarbonylation of styrene.

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate and compare the chemical structures of poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) in air, in water, and in a non-polar solvent, FC-75. SFG spectra from both polymer surfaces in air are dominated by vibrational modes from the ester ethyl side groups. The average orientation of these ester ethyl groups on the two polymer surfaces is slightly different. In water, the two polymers show markedly different restructuring behavior. The ester ethyl side chains on the PEMA surface in water reorient to tilt more toward the surface, yet remain ordered. Such a restructuring of the PEMA surface in water is reversible. However, no SFG signal was detected from the PEA/water interface, showing that the surface of PEA becomes disordered upon contacting water, and this process is irreversible. SFG results collected from the C=O range indicate that hydrogen bonding is observed for both polymer/water interfaces, but the order of C=O at the PEA/water interface is much lower than that at the PEMA/water interface. Supplemental experiments support our hypothesis that the PEA surface becomes rough and loses order gradually as it interacts with water. We have demonstrated, for the first time, that the loss of surface structural order is due to the interaction between soft PEA chains with water molecules followed by reorganization of the polymer backbone. This causes the polymer surface to become rough and disordered. However, the surface structures of PEMA and PEA in FC-75 are similar and are also similar to those in air. This indicates that not only T(g), but also the contacting medium plays an important role in determining the surface restructuring behavior of polymer materials.

The fluoroaryl phosphines P{C6H3(CF3)2-3,5}3 (La) and P(C6F5)3 (Lb) form the complexes trans-[MCl2(La)2] and trans-[MCl2(Lb)2](M = Pd or Pt) which have been isolated and fully characterised. 31P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = Lb< La

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.