Monotitanocene catalysts: an ESR study of Ti(III) derivatives formed in presence of MAO and other organoaluminium compounds

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

“…5) indicating the formation of paramagnetic species with g values g = 1.9958 (DH = 0.318 mT), g = 1.9871 (DH = 0.79 mT) and g = 1.9741 (DH = 1.381 mT). The last value is close to the one characteristic for species of general formula CpTi(l-Cl(or Me)) 4 Al 2 (Cl(or Me) 4 arising from the reduction of Ti(IV) by free AlMe 3 (see Section 4) known to be contained in MAO [29]. Surprisingly, the formation of Ti(III) hydrido species reported for the CpTiCl 3 /MAO mixture yielding doublets in the EPR spectrum at g = 1.995 and g = 1.989 [30] was not observed for the case of the 4/MAO mixture.…”

“…Tetramethylcyclopentadiene (a mixture of isomers) [32], TiCl 3 (THF) 3 [33] and [l-(SiMe 2 ){(g 5 -C 5 H 4 )TiCl 3 } 2 ] (6) [11] were prepared by published procedures. 1 H (300.0 MHz), 13 C (75.4 MHz) 29 Si(59.6 MHz) NMR spectra of ligands and organometallic species were recorded on a Varian Mercury 300 spectrometer in CDCl 3 solutions at 293 K. Chemical shifts (d/ppm) are given relative tetramethylsilane as internal standard. 1 H and 13 C NMR spectra of PE samples were measured in CD 2 Cl 4 at 105°C on a Bruker Avance 500 MHz spectrometer and are referenced to residual solvent signal (5.99 ppm) for 1 H and to the signal of main PE chain at 30.00 ppm for 13 C. EPR spectra were measured on an ERS-220 spectrometer (Center for Production of Scientific Instruments, Academy of Sciences of GDR, Berlin, Germany) operated by a CU-3 unit (Magnettech, Berlin, Germany) in the X-band.…”

Synthesis, characterization and catalytic activity of the complex titanium bis(dimethylmalonate)–bis(diethylamido) in the polymerization of propylene

“…7a) showed a superposition of at least three (Ti-1, Ti-2, Ti-3) asymmetrical signals with up field-shifted g-factors (compared to organic radicals) at g = 1.991-1.972. Such low values of g-factor are typically exhibited by paramagnetic Ti 3+ complexes [78][79][80]. An additional signal with a hyperfine structure [a (3H) = 3.43 G, g = 2.0017] was observed.…”

Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization

“…29 The formation of a number of open-shell Ti(III) species upon MAO/MMAO activation was demonstrated through conventional continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy in solution. [30][31][32] Furthermore, quantitative 1 H NMR analysis of the syndiotactic polystyrene produced under quasi living polymerization conditions (polydispersity index (PDI) ¼ 1.3-1.6) by these catalysts demonstrated that Ti(III)-H species are involved in the initiation reaction and that a stationary concentration ($20% of the paramagnetic fraction) is produced under polymerization conditions through a reversible insertion-elimination of the growing polymer chain. 33 Despite their relevance, the chemical structure of such openshell Ti(III) hydride complexes and the origin of these species are still an open question of great interest in MAO activated halftitanocene catalysis.…”