Bis[η⁵-tetramethyl(trimethylsilyl)cyclopentadienyl]titanium(II) and Its π-Complexes with Bis(trimethylsilyl)acetylene and Ethylene

Abstract

Thermally induced elimination of bis(trimethylsilyl)acetylene from its titanocene complex [{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiC⋮CSiMe3)] (1) afforded the stable titanocene [{η5-C5Me4(SiMe3)}2TiII] (2) in high yield under mild conditions. Compound 2 exhibits paramagnetic line broadening of 1H NMR signals, although it is silent in EPR spectra down to −196 °C. The solid-state structure determination revealed an exactly parallel arrangement of the cyclopentadienyl rings in 2 due to crystallographically imposed symmetry. Complex 2 smoothly reacts with ethylene to give the yellow η2-ethylene complex [{η5-C5Me4(SiMe3)}2Ti(η2-CH2CH2)] (3). The structures of 1 and 3, determined by single-crystal X-ray diffraction, show the bent-titanocene moieties with the η2-coordinated Me3SiC⋮CSiMe3 and CH2CH2 ligands, respectively.

Zirconium Bis(indenyl) Sandwich Complexes with an Unprecedented Indenyl Coordination Mode and Their Role in the Reactivity of the Parent Bent‐Metallocenes: A Detailed DFT Mechanistic Study

“…[3a, 6] In fact, the only examples published until the present are titanium compounds of cyclopentadienyl ligands with bulky substituents (C 5 Me 4 R À ). [7][8][9] Analogous species with zirconium and hafnium have been more elusive and their attempted synthesis unsuccessful, probably due to the known tendency of those metals to attain their highest oxidation states and, thus, the relative instability of the corresponding lowvalent complexes. Nevertheless, the presence of zirconocene intermediates, [ZrCp' 2 ] (Cp' = substituted cyclopentadienyl), has been hinted by a number of studies, including its role in catalytic processes [2] and trapping with donor ligands or even dinitrogen.…”

Bis(trimethylsilyl)acetylene Complexes of Titanocenes and Zirconocenes: Their Recent Chemistry and Reactions with Lewis Acids

“…[18] The formation of stable substituted titanocenes by elimination of bis(trimethylsilyl)acetylene from the corresponding alkyne complexes has been documented in some excellent papers by Mach and coworkers. [26,27] The reaction of 2a, 2b, or 6 with norbornadiene or benzonorbornadiene proceeds with elimination of the alkyne (and THF or pyridine) to give zirconacyclopentanes bearing additional functional groups (Scheme 2). [28] Note that in almost all reaction schemes the elimination of coligands and/or bis(trimethylsilyl)acetylene is omitted for simplicity.…”

Synthesis and structure of isopropyldimethylsilyl-substituted octamethyltitanocene

“…The stability of titanocenes [Ti(g 5 -C 5 Me 4 R) 2 ] and their nitrogen complexes follow opposite trends. The thermal stability of the nitrogen complexes was found to be decreasing in the order of R: Me > Pr i > SiMe 3 > Bu t [5], and for the titanocenes it is only known that the titanocene for R = SiMe 3 is stable at 70°C [2] whereas that for R = Me forms an equilibrium with its hydride at room temperature [4]. A similar trend applies also to titanocene-btmse complexes.…”

“…Thermally stable, well-defined crystalline titanocenes are known only a few, all of them containing triorganylsilyl group in addition to four methyl groups on each of the two cyclopentadienyl ligands [1][2][3]. The titanocene containing tert-butyldimethylsilyl group was obtained from the appropriate titanocene monochloride by the reduction with sodium amalgam [1], that one containing trimethylsilyl group by thermolysis of its bis(trimethylsilyl)ethyne (btmse) complex [2], and the titanocenes containing phenethyldimethylsilyl and methyldiphenylsilyl groups were prepared by a direct reduction of the particular titanocene dichloride by magnesium in tetrahydrofuran (thf) [3] (Chart 1).…”

“…The titanocene containing tert-butyldimethylsilyl group was obtained from the appropriate titanocene monochloride by the reduction with sodium amalgam [1], that one containing trimethylsilyl group by thermolysis of its bis(trimethylsilyl)ethyne (btmse) complex [2], and the titanocenes containing phenethyldimethylsilyl and methyldiphenylsilyl groups were prepared by a direct reduction of the particular titanocene dichloride by magnesium in tetrahydrofuran (thf) [3] (Chart 1). Decamethyltitanocene [4] seems to be further stabilized by the replacement of one methyl group on each cyclopentadienyl ligand by a more bulky group, like iso-propyl or tert-butyl [5].…”