Yanping Ma

Elastomeric polyethylenes accessible via ethylene homo-polymerization using an unsymmetrical α-diimino-nickel catalyst

Five types of unsymmetrical bis(arylimino)acenaphthenes, 1-[2,4,6-(CHPh2)3C6H2N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2Ph L1, 2,6-Et2Ph L2, 2,6-i-Pr2Ph L3, 2,4,6-Me3Ph L4 and 2,6-Et2-4-MePh L5), each containing a single N-2,4,6-tribenzhydrylphenyl group, have been prepared and fully characterized. The interaction of L1–L5 with (DME)NiBr2 (DME = 1,2-dimethoxyethane) afforded the corresponding 1 : 1 nickel(II) bromide chelates, LNiBr2 (Ni1–Ni5), in good yield. Distorted tetrahedral geometries are a feature of the X-ray structures of Ni1 and Ni3; broad paramagnetically shifted peaks are seen in the 1H NMR spectra for all the nickel complexes in solution. Upon activation with relatively low amounts of Et2AlCl or Me2AlCl (200–700 equivalents), Ni1–Ni5 exhibited exceptionally high activities for ethylene polymerization (up to 1.07 × 107 g of PE (mol of Ni)−1 h−1), displayed good thermal stability [2.97 × 106 g of PE (mol of Ni)−1 h−1 even at 90 °C] and produced hyperbranched polyethylenes. Dynamic mechanical analysis and stress–strain testing reveal that the polymeric materials possess good elastomeric recovery and high elongation at break, indicating a promising alternative material to thermoplastic elastomers (TPEs).

Efficient acceptorless dehydrogenation of secondary alcohols to ketones mediated by a PNN-Ru(II) catalyst

Four types of ruthenium(II) complexes, [fac-PNN]RuH(PPh3)(CO) (A), [fac-PNHN]RuH(η1-BH4)(CO) (B), [fac-PNHN]RuCl2(PPh3) (C) and [fac-PNHN]RuH(η1-BH4)(PPh3) (D) (where PNHN and PNN are N-(2-(diphenylphosphino)ethyl)-5,6,7,8-tetrahydroquinoline-8-amine and its deprotonated derivative), have been synthesized and assessed as catalysts for the acceptorless dehydrogenation of secondary alcohols to afford ketones. It was found that C, in combination with t-BuOK, proved the most effective and versatile catalyst allowing aromatic-, aliphatic- and cycloalkyl-containing alcohols to be efficiently converted to their corresponding ketones with particularly high values of TON achievable. Furthermore, the mechanism for this PNN-Ru mediated process been proposed on the basis of a number of intermediates that have been characterized by EI-MS and NMR spectroscopy. These catalysts show great potential for applications in atom-economic synthesis as well as in the development of organic hydride-based hydrogen storage systems.

Direct Hydrogenation of a Broad Range of Amides under Base‐free Conditions using an Efficient and Selective Ruthenium (II) Pincer Catalyst

The ruthenium(II) complex, [fac‐PNHN]RuH(η1‐BH4)(CO) (B; PNHN=8‐(2‐diphenylphosphinoethyl)aminotrihydroquinoline), is a highly versatile and effective catalyst (loadings of 0.1–1 mol %) for the hydrogenation of a multitude of amides, which include primary, secondary, and tertiary amides, to give their corresponding alcohols and amines in high yields under base‐free conditions. All products were confirmed by using GC and GC–MS.

Dinuclear Nickel(II) Chlorides Bearing N , N '-bis(5,6,7-trihydroquinolin-8-ylidene)-[1,1'-biphenyl]-4,4'-diamines: Synthesis and Ethylene Polymerization

Abstract5,6,7-Trihydroquinolin-8-one was condensed with the corresponding benzidine to give N,N′-bis(5,6,7-trihydroquinolin-8-ylidene)-[1,1′-biphenyl]-4,4′-diamine derivatives (L1–L3). The ligands were reacted with two equivalents of NiCl2·6H2O in a mixture of EtOH and CH2Cl2 to afford the corresponding dinickel(II) chloride complexes (Ni1−Ni3). The organic compounds were completely characterized, whilst the bi-metallic complexes were characterized by FTIR spectra and elemental analysis. These nickel complexes exhibited high activities towards ethylene polymerization in the presence of either MAO or Me2AlCl, maintaining a high activity over a prolonged period. The obtained polyethylenes were confirmed as having low molecular weights by GPC analysis.

An air and moisture tolerant iminotrihydroquinoline-ruthenium(II) catalyst for the transfer hydrogenation of ketones

Reaction of 8-amino-5,6,7,8-tetrahydroquinoline with RuCl2(PPh3)3 at room temperature affords the ruthenium(ii) chelate (8-NH2-C9H10N)RuCl2(PPh3)2 (E), in which the two triphenylphosphine ligands are disposed mutually cis. By contrast, when the reaction is performed at reflux ligand oxidation/dehydrogenation occurs along with cis-trans reorganization of the triphenylphosphines to form the 8-imino-5,6,7-trihydroquinoline-ruthenium(ii) complex, (8-NH-C9H9N)RuCl2(PPh3)2 (F). Complex F can also be obtained in higher yield by heating a solution of E alone to reflux. Comparison of their molecular structures highlights the superior binding properties of the bidentate imine ligand in F over its amine-containing counterpart in E. Both complexes are highly effective in the transfer hydrogenation of a wide range of alkyl-, aryl- and cycloalkyl-containing ketones affording their corresponding secondary alcohols with loadings of as low as 0.1 mol%. Significantly, F can deliver excellent conversions even in bench quality 2-propanol in reaction vessels open to the air, whereas the catalytic efficiency of E is diminished by the presence of air but only operates efficiently under inert conditions.