Structure and reactivity of bis(pentamethylcyclopentadienyl)(ethylene)titanium(II), a simple olefin adduct of titanium

Abstract

The synthesis and an X-ray diffraction study of bis(pentamethylcyclopentadienyl)(ethylene)titanium 2Ti(?j-C2H4)] are reported. This complex represents the first example of an isolable ethylene adduct of titanium. Titanium-olefin complexes have been widely invoked as key intermediates in Ziegler-Natta olefin polymerization schemes. Whereas treatment of (7j-C5Me5)2Ti(?;-C2H4) with ethylene leads to only traces of polymer after months, (n-C5Me5)2Ti(7)-C2H4) participates in a range of stoichiometric and catalytic reactions. These include the catalytic conversion of ethylene specifically to butadiene and ethane and the catalytic isomerization of alkenes.'H, 12H, and 13C NMR spectra were recorded on Varían T-60 and EM-390, JEOL FX90Q, and Bruker WM-500 spectrometers. Spectra were taken in benzene or toluene solutions, and data are referenced to

A model for the homogeneous isospecific Ziegler–Natta polymerization of olefins: Enantioselectivity in the deuteration and deuteriooligomerization of 1‐alkenes

“…'~ As in ref. 4, the geometric parameters relative to the coordinated olefines have been derived from the crystal structure of bis(pentamethy1-cyclopentadienyl)(ethene)titanium, 26 and from the crystal structure of bis(pentamethylcyc1openta-dienyl)(styrene)niobium hydride." The distance Zr-C (chain) has been assumed to be 2.29 A, as observed in some u-alkyl Zr complexes,28 while the distance Zr-C (olefin) has been set equal to 2.31 A, that is 0.02 A larger than the distance Zr-C (chain), to be consistent with the analogous distances observed in titanium c o m p l e x e~.~~~~~-~~ The distance Zr-D has been set equal to 1.73 A, that is the sum of the covalent radii of the Zr and H atoms.,,…”

Effizienter Zugang zu Titanaaziridinen durch C‐H‐Aktivierung von N‐Methylanilinen bei Raumtemperatur

“…Dabei erweist sich die 13 C-chemische Verschiebung (d = 66.2) für die TiCH 2 -Gruppierung als besonders signifikant. [27,28] Das im Ring enthaltene tertiäre C-Atom (*) induziert als Asymmetriezentrum das Auftreten diastereotoper Signale der Metalloceneinheit (acht Signale) sowie die Aufspaltung der Methylenringprotonen Ti-CH 2 -( je 1H,m ,d = 1.13;2 .62) bzw.N -CH 2 (je 1H,m ,d=2.89, 3.22). [15] Die gefundene 15 N-Verschiebung erfährt beim Übergang von drei-zu fünfgliedri-gen Ringen eine Hochfeldverschiebung (3b d=220, 6 d = 191).…”

Efficient Access to Titanaaziridines by CH Activation of N‐Methylanilines at Ambient Temperature

“…[15] TheN MR spectra of 6 reveal that only one structural isomer is formed (shown in Scheme 4), with the C 4 H 9 -substituent in the position b to the titanium center as evident by the 13 Cchemical shift (d = 66.2 ppm) which is characteristic of the TiCH 2 -group. [27,28] Thet ertiary carbon atom (marked with a*i nS cheme 4)) as as tereogenic center, which is situated in the ring structure,i nduces the appearance of diastereotopic signals of the metallocene (eight signals), as . .…”