Andrew D. Horton

Phospholyl catalysts for olefin polymerization

Abstract Seventeen different phospholyl ligands were incorporated in a total of 22 zirconium complexes, (Phos) 2 ZrCl 2 , (Phos)(C 5 H 5 )ZrCl 2 , investigated in propylene polymerization catalysis using methylaluminoxane as cocatalyst. Atactic polypropylene with M n varying from 450 to >20 000 and vinylidene end groups (CH 2 C(Me)R) was obtained with activities up to 170 kg/g Zr·h. For the 11 diphospholyls of structure (2,5-R 2 C 4 H 2 P) 2 ZrCl 2 , catalytic activity was highest with substituents of moderate bulk adjacent to phosphorus (e.g., c -Pr, Ph), whereas complexes with two small (H) or two large (CMe 3 , SiMe 3 ) ligand substituents were inactive. It is hypothesized that optimum activity with MAO requires selective blocking of phosphorus lone pair coordination to aluminum, whilst allowing free propylene approach to the active site. The degree of polymerization increased steadily in the series of 2,5-disubstituted phospholyl complexes, dialkyl M n .

New highly active and selective Et oligomerization catalysts based on cationic diamide zirconium complexes

Group 4 complexes based on the diamide ligand, [Me3CN(SiMe 2 ) 2 NCMe 3 ] 2- , have been investigated as possible catalysts for olefin conversions. The dialkyl complexes, (Me 2 SiNCMe 3 ) 2 ZrR 2 (R = CH 2 Ph, Me), were converted into zwitterionic (X-ray: {Me 2 SiNCMe 3 } 2 Zr(η I -Bz){η II -BzB(C 6 F 5 ) 3 }), or cationic mono-alkyl compounds by reaction with B(C 6 F 5 ) 3 or borate reagents. These electrophilic species catalyzed ethylene oligomerization, affording highly linear alpha-olefins under mild conditions (C 6 fraction > 99.5 % 1-hexene at 50 °C, 6 bar). The highest activities (290 Kg/g Zr.h) were obtained in toluene solvent using tri-iso-butylaluminium (TIBA) as scavenger. The catalyst exhibited activity decay in alkane solvent, which was countered by replacement of TIBA by more crowded trialkylaluminium scavengers or branched alkylaluminoxane scavengers. The product consisted primarily of linear alpha-olefins (LAO) with low levels of remote-branched AOs. These are formed by successive insertion of higher olefin and one or more ethylenes in a growing chain, followed by chain transfer.

NOE-derived solution structures of a benzylborato-azasilazirconacyclobutane complex, {l_brace}(Me{sub 3}Si){sub 2}N{r_brace}Zr(CH{sub 2}SiMe{sub 2}NSiMe{sub 3}){l_brace}{eta}{sup 6}-PhCH{sub 2}B(C{sub 6}F{sub 5}){sub 3}{r_brace}

The benzylborato-azasilazirconacyclobutane complex 1 was formed by ligand cyclometalation upon reaction of {l_brace}(Me{sub 3}Si){sub 2}N{r_brace}{sub 2}Zr(CH{sub 2}Ph){sub 2} with B(C{sub 6}F{sub 5}){sub 3}. Quantitative analysis of the {sup 1}H NOESY time course of 1 using the conformer population analysis method demonstrates that the dominant conformers in solution are rapidly exchanging benzyl borate rotamers, closely bound to the asymmetric zirconium. The ring rotates such that the benzylic methylene eclipses the metallocyclobutylmethylene in the majority of the population and the free amide nitrogen in the minority of the population. A molecular dynamics approach was required to solve this solution structure because a mixture of static conformations does not satisfactorily explain the observed spectra.

Re-evaluating selectivity as a determining factor in peroxidative methane oxidation by multimetallic copper complexes†

A series of multimetallic copper(II) complexes have been re-investigated for methane oxidation with H2O2. The preparation and properties of trinuclear copper(II) complexes of the form [Cu3(triazole)n(OH2)12−n] (n = 8, 10) are reported. While these complexes are trimeric in the solid-state, 1H NMR studies suggest that facile ligand dissociation occurs in solution. The oxidation of cyclohexane with H2O2 catalyzed by [Cu3(triazole)n(OH2)12−n] (n = 8, 10) is compared against a literature known oxo-centered tetrameric cluster (Angew. Chem., Int. Ed., 2005, 44, 4345) and these catalysts display moderate activities. The series have also been investigated in methane oxidation at 30 bar and 40 °C. Analytical techniques including a solvent suppression 1H NMR method have been applied to quantify the liquid- and gas-phase products. The multi-metallic copper(II) complexes and copper(II) nitrate control samples produce only methanol and CO2. While TONs for methanol production range from 1.4–4.6 in all cases approximately 50 times the amount of CO2 is produced relative to methanol. We conclude that selectivity is a determining factor in methane oxidation under these conditions and should be considered in future studies.