- Mono- and bi-nuclear molybdenum complexes of 2,6-bis(diphenylphosphino)-N-methylaniline
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The new ligand 2,6-bis(diphenylphosphino)-N-methylaniline (LH) has been prepared via repeated o-lithiation of lithium N-methyl-N-phenylcarbamate.Reaction of LH with Mo(CO)6 gives Mo(CO)4 (1) and (with an excess of Mo(CO)6) (μ-P,N:P'-LH)M
- Oort, A. Bart van,Budzelaar, Peter H.M.,Frijns, John H.G.,Orpen, A. Guy
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- Application of supramolecular bidentate hybrid ligands in asymmetric hydroformylation
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In this study we report a novel class of supramolecular bidentate hybrid ligands in which the two inequivalent phosphorus units and pyridine moieties are covalently attached to a chiral scaffold and the supramolecular interactions are used as a second handle to control the coordination sphere around the transition-metal centre. The coordination chemistry of these ligands was investigated under hydroformylation conditions by high-pressure NMR and IR spectroscopy, revealing the formation of a single active species in which the phosphane ligand is in the axial position and the phosphoramidite adopts the equatorial position. These ligands were applied in the asymmetric Rh-catalysed hydroformylation of styrene and para-substituted analogues. In these hydroformylation reactions, modification of the electronic and steric properties of the zinc(II)-templates appear to have a significant influence on the activity and selectivity of the catalysis. In particular, zinc(II)-templates bearing more electron-withdrawing substituents led to an increase in enantioselectivity.
- Bellini, Rosalba,Reek, Joost N. H.
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p. 13510 - 13519,10
(2012)
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- Preparation of phosphine-amido hafnium and zirconium complexes for olefin polymerization
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Aniline (N-R-C6H5NH) and 1,2,3,4-tetrahydroquinoline (2-R-C9H9NH) derivatives were ortho-lithiated via conversion of the respective -NH groups to -N(COOLi), followed by treatment with tBuLi. The resulting ortho-lithiated compounds were transformed to ortho-Ph2P-substituted derivatives on treatment with Ph 2P(OPh). Further reaction of the resulting compounds with M(CH 2Ph)4 (M = Zr, Hf) afforded a series of Hf and Zr complexes: (2-R-8-Ph2PC9H9N)Hf(CH 2Ph)3 (8, R = H; 9, R = Me; 10, R = iPr; 11, R = nBu), (N-R-2-Ph2PC6H4N)Hf(CH2Ph) 3 (12, R = Me; 13, R = Et; 14, R = iPr), (2-R-8-Ph2PC 9H9N)Zr(CH2Ph)3 (15, R = H; 16, R = Me; 17, R = iPr; 18, R = nBu), and (N-R-2-Ph2PC6H 4N)Zr(CH2Ph)3 (19, R = Me; 20, R = Et)]. X-ray crystallographic studies of 9, 14, 16, and 19 revealed a distorted trigonal-bipyramidal structure with two benzyl moieties in equatorial positions and the remaining benzyl ligand occupying an apical position; in solution, however, three benzyl ligands became scrambled, as evidenced by a single set of benzyl signals in the corresponding 1H NMR spectra. The complexes showed comparable activities (17-48 × 106 g/mol-M·h) to the Ti-based constrained geometry catalyst (CGC) (36 × 106 g/mol-Ti·h) in ethylene/1-octene copolymerization, despite their inferior 1-octene incorporation capabilities (3-8 mol % versus 17 mol %). Compound 15 showed a moderate 1-octene incorporation capability (7.7 mol %), whereas the others showed low 1-octene incorporations (2-4 mol %). Compounds 9 and 16 provided high-molecular-weight polymers with Mw > 200 000 even at high reaction temperatures of 100-130 C.
- Jun, Sung Hae,Park, Ji Hae,Lee, Chun Sun,Park, Seong Yeon,Go, Min Jeong,Lee, Junseong,Lee, Bun Yeoul
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p. 7357 - 7365
(2014/04/03)
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- Supramolecular hybrid bidentate ligands in asymmetric hydrogenation
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In this study we introduce a novel class of supramolecular bidentate hybrid ligands and their application in the rhodium-catalysed asymmetric hydrogenation of prochiral olefins. A new supramolecular strategy is reported in which the two nonequivalent phosphorus atoms are linked covalently to a chiral scaffold, and the supramolecular interactions are used to control the second coordination sphere of the transition-metal catalyst. The supramolecular assembly is formed in situ by selective interaction between the nitrogen-donor atoms and the zinc(II) template, which is essential for obtaining high activity and selectivity. The investigations of the different zinc(II) and ruthenium(II) templates on the reaction parameters revealed a dependence of the activity and selectivity on the association constant between the supramolecular template and the pyridyl ligands. The scope of the supramolecular assemblies was explored in the Rh-catalysed asymmetric hydrogenation of α-dehydroamino acid esters and Roche ester derivatives. High activities and good to excellent enantioselectivities up to 99 % ee were obtained with the supramolecular ligands. Application of the supramolecular strategy on the basis of variations of the steric and electronic properties of zinc(II) templates demonstrate that these changes can influence key reaction parameters such as activity and selectivity. Copyright
- Bellini, Rosalba,Reek, Joost N. H.
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p. 4684 - 4693
(2013/01/15)
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- Catalytic scaffolding ligands: An efficient strategy for directing reactions
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The design and application of a scaffolding ligand that promotes branch and diastereoselective hydroformylation of terminal olefins as well as the regio- and diastereoselective hydroformylation of disubstituted olefins is reported. It is shown that the ligand covalently and reversibly bonds to the substrate, allowing for directed hydroformylation. As the substrate ligand interaction is dynamic, hydroformylations are catalytic in ligand and do not require any additional synthetic steps to add or remove the directing group. Using a catalytic quantity of a scaffolding ligand (20-25 mol %), excellent regioselectivity for disubstituted olefins (up to 98:2) and high branch selectivity (up to 88:12) for terminal olefins were obtained. Copyright
- Lightburn, Thomas E.,Dombrowski, Michael T.,Tan, Kian L.
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supporting information; experimental part
p. 9210 - 9211
(2009/02/03)
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- Preparation of Hybrid Bidentate Phosphine Ligands by Reduction of Their Benzyl- or Phenyl-phosphonium Salts. X-Ray Crystal Structure of 2-Aminophenyltriphenylphosphonium Tetrachloronickelate(II)
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The 2-substituted phenylphosphine bidentate hybrid ligands, 2-aminophenyl-, 2-methylaminophenyl-, 2-hydroxyphenyl- and (2-amino-3-methylphenyl)-diphenylphosphine, (1a-d), respectively, and 2-aminophenylmethylphenylphosphine, (1e), were synthesized by reduction of their phenylphosphonium halides, (2a-e)X (X = Cl or Br), with sodium naphthalenide in tetrahydrofuran at -68 deg, or electrochemically at a mercury cathode.The phosphonium salts were prepared by reaction of triphenylphosphine with aryl halide and anhydrous nickel halide at 200 deg.X-Ray diffraction of (2a)2 showed it to have monoclinic space group P21/n, a 10.657(4), b 20.966(3), c 20.422(6) Angstroem, β 101.33(2) deg and Z 4.The structure was refined by a full-matrix least-squares procedure to a final R 0.050 for 3534 reflections with I > 2.5?(I).
- Cooper, Mervyn K.,Downes, J. Michael,Duckworth, Paul A.,Tiekink, Edward R. T.
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p. 595 - 609
(2007/10/02)
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