Mirko Kranenburg

A remarkable inversion of structure–activity dependence on imido N-substituents with varying co-ligand topology and the synthesis of a new borate-free zwitterionic polymerisation catalyst

Ethylene polymerisation productivities of tris(pyrazolyl)methane-supported catalysts [Ti(NR){HC(Me2pz)3}Cl2] show a dramatically different dependence on the imido R-group compared to those of their TACN analogues, attributed to differences in fac-N3 donor topology; when treated with AliBu3, the zwitterionic tris(pyrazolyl)methide compound [Ti(N-2-C6H4tBu){C(Me2pz)3}Cl(THF)] also acts as a highly active, single site catalyst (TACN = 1,4,7-trimethyltriazacyclononane).

Discovery and evaluation of highly active imidotitanium ethylene polymerisation catalysts using high throughput catalyst screening

A family of ca. 50 imidotitanium precatalysts [Ti(NR)(Me(3)[9]aneN(3))Cl(2)](R = alkyl or aryl; Me(3)[9]aneN(3)= 1,4,7-trimethyltriazacyclononane) were prepared in good yields using semi-automated procedures; high-throughput screening techniques identified seven highly active ethylene polymerisation precatalysts with activities in the range ca. 3 400 to 10 000 kg(PE) mol(-1) h(-1) bar(-1).

Continuous wave and pulse EPR as a tool for the characterization of monocyclopentadienyl Ti(III) catalysts

Monocyclopentadienyl Ti(III) catalysts in which the cyclopentadienyl ring has a heteroatom-functionalized side chain are used in the polymerization of olefins and the co-polymerization of ethylene with propylene, 1-hexene, 1-octene and styrene. In this work, we show that a combined continuous wave and pulse EPR study of such complexes can reveal structural information where other analytical methods fail. Hyperfine sublevel correlation (HYSCORE) spectroscopy is found to be a powerful method to identify the type of nuclei surrounding the Ti 3 + ion. For the first time, the hyperfine and nuclear quadrupole data of Ti(III)-bound 14 N nuclei are reported. The observed values are compared to known data of different transition metal complexes. Furthermore, the observed proton and lithium interactions are discussed.

Characterization of a metallocene/co-catalyst system supported on silica by Fourier-Transform Raman spectroscopy

Abstract 2,2′-bis-(indene-2-yl)-biphenyl-Zirconium dichloride (biph[2-Ind] 2 ZrCl 2 ) supported on silica and in the presence of methylaluminoxane (MAO) cocatalyst was studied by FT-Raman spectroscopy. Even though the transition metal was present at a concentration down to 0.12 wt.%, useful FT-Raman spectra were obtained. The aim of this work was to correlate spectral features to such typical catalyst properties like Al/Zr ratio and catalytic yield (CY). The Raman spectra contain signals due to the co-catalyst and the catalyst. Catalyst signals due to ZrCl, ZrCH 3 and Zr-other ligand (e.g. Cp or Biph-2-Indene) bonds as well as ligand specific signals were identified using literature data, model compounds and ab-initio quantum chemical calculations of the vibrational spectra. An excellent correlation was found between the intensity ratio of the peaks at 3000 and 1500 cm −1 and the Al/Zr ratio. A fairly linear correlation was found between the signal intensity due to MCH 3 bonds and the catalytic yield (kg PE per mmole Zr) for a series of samples of different Al/Zr ratios and different catalytic yields.

Diphosphines with Large Natural Bite Angles Lead to the Formation of Non-Classical cis-(diphosphine)2Ru(H)(H2)+ Complexes

The application of diphosphine ligands with large natural bite angles leads to the formation of thermo-labile, non-classical cis-(diphosphine) 2 Ru(H)(H 2 ) + complexes.

Palladium(0)–tetracyanoethylene complexes ofdiphosphines and a dipyridine with large bite angles, and their crystalstructures

Complexes of Pd(tcne) (tcne = tetracyanoethylene) containing bidentate ligands with large bite angles, bis[2-(diphenylphosphino)phenyl] ether (L 1 ), 4,6-bis(diphenylphosphino)-10,10-dimethyl-10H-dibenzo[b ,e][1,4]oxasiline(L 2 ), 4.6-bis(diphenylphosphino)-2,8-dimethylphenoxathiine (L 3 ), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (L 4 ) and trans-5,6-bis(2-pyridyl)bicyclo[2.2.1]hept-2-ene (L 6 ), were prepared and characterised. The compound 4,6-bis(diphenylphosphino)dibenzo[b,d]furan (L 5 ) did not form chelating palladium complexes, owing to its large natural bite angle of 138°. The crystal structures of L 6 , [PdL 1 (tcne)]·2.5CH 2 Cl 2 1, [PdL 2 (tcne)]·4CH 2 Cl 2 2, [PdL 4 (tcne)]·2CH 2 Cl 2 4 and [PdL 6 (tcne)] 5 have been determined. The similarity of electronic effects induced by the free diphosphines was demonstrated by MOPAC calculations. The geometries of the ligands, however, were most accurately predicted by molecular mechanics (MM2) calculations for the diphosphines, and MNDO for L 6 . The largest P–Pd–P angle in the zerovalent palladium complexes was found to be 104.6°. A further increase in the natural bite angle of the ligand results in elongation of the Pd–P bond length in the complex rather than enlargement of the P–Pd–P bite angle. The ligand L 6 assumed a bite angle of 99.5(2)° in complex 5, which is considerably smaller than its calculated value of 117°.