Dihydrogen Activation by Titanium Sulfide Complexes

Abstract

The titanocene sulfido complex Cp* 2 Ti(S)py (1, Cp* = pentamethylcyclopentadienyl; py = pyridine) is synthesized by addition of a suspension of S 8 to a toluene solution of Cp* 2 Ti-(CH 2 CH 2 ) (2) and py. The rate of rotation of the pyridine ligand in solution was determined by 1 H NMR spectroscopy, and the structure of 1 was determined by X-ray crystallography. Complex 1 reacts reversibly with dihydrogen to give Cp* 2 Ti(H)SH (6) and py. Reaction of 1 with HD gives an equilibrium mixture of Cp* 2 Ti(D)SH and Cp* 2 Ti(H)SD; H 2 and D 2 are not formed in this reaction. 1D 1 H NMR magnetization transfer spectra and 2D EXSY 1 H NMR spectra of 6 in the presence of H 2 show that in solution the H 2 , hydride, and hydrosulfido hydrogen atoms exchange. A four-center mechanism for this exchange is proposed. The EXSY studies show that the Ti-H and S-H hydrogens exchange with each other more rapidly than either of those hydrogens exchanges with external H 2 . A transient dihydrogen complex intermediate is proposed to explain this observation. The infrared spectrum of 6 shows an absorption assigned to the Ti-H stretching mode at 1591 cm −1 that shifts upon deuteration to 1154 cm −1 . Reaction of 1 with trimethylsilane, diethylsilane, or dimethylsilane gives Cp* 2 -Ti(H) SSiMe 3 (7), Cp* 2 Ti(H)SSiHEt 2 (8), or Cp* 2 Ti(H)SSiHMe 2 (9), respectively. The isotope effect for the reaction producing 7 has been measured, and a mechanism is proposed. Treatment of 1 with an additional equivalent of S 8 results in the formation of the disulfide Cp* 2 Ti(S 2 ) (4). Acetylene inserts into the Ti-S bond of 4 to produce the vinyl disulfide complex 5. The structures of 4 and 5 have been determined by X-ray diffraction. Compound 4 reacts with 2 in the presence of py to produce 1. Phosphines react with 4 in the presence of H 2 to provide 6 and the corresponding phosphine sulfide. Reaction of hydrogen with 4 gives Cp* 2 -Ti(SH) 2 (3). The reactions of 1 and 4 with dihydrogen provide a model for possible mechanisms of H 2 activation by metal-sulfide hydrodesulfurization catalysts.

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

“…An intramolecular rearrangement of the vinyl disulfide (42) into the corresponding dithiolene (41) takes place at 90°C, suggesting that it is an intermediate in the formation of the dithiolene complex in other reactions (typically performed at high temperature). The disulfido complex, Cp à 2 TiðS 2 Þ, also reacts with acetylene to form a vinyl disufide complex that has been structurally characterized [101]. Vinyl sulfide complexes, Cp à 2 ZrðSC 2 R 2 Þ, were similarly formed in the reactions of Cp à 2 Zr@S or Cp à 2 ZrSðpyridineÞ with RCCR (R = Et, Ph, tol) [102].…”

N–H Group Transfer and Oxidative Addition Chemistry Promoted by Isolable Bis(cyclopentadienyl)titanium Sandwich Complexes

“…[6,7] Exposure of each of the monomeric, base-free titanocene oxo complexes to H 2 results in rapid hydrogenation of the Ti=O bond to furnish the corresponding hydroxy hydride derivatives, (η 5 -C 5 Me 4 R) 2 Ti(OH)H. This behavior highlights the benefits of the base-free species as addition of dihydrogen to (η 5 -C 5 Me 5 ) 2 Ti(O)L (L = pyridine) yields a mixture of products from which (η 5 -C 5 Me 5 ) 2 Ti(OH) 2 and (η 5 -C 5 Me 5 ) 2 Ti(OH)H were identified. [8] The pressure dependence on the rate of hydrogenation of 2=O established a first order dependence on H 2 . [5] This rate law, in combination with the measurement of a normal, primary kinetic isotope effect of 2.7(3) at 23°C, supports a 1,2-addition pathway for hydrogenation of the Ti=O bond.…”

The pure rotational spectrum of TiS (X3Δr) at submillimeter wavelengths

“…TiS 2 is also a semiconductor material, and is widely used as the active cathode component in lithium batteries [2]. Titanium sulfide complexes have been shown to activate H 2 [3], and TiS clusters have been created with interesting geometries, stabilized by bridging oxygen atoms [4]. TiS has also been observed in the gas-phase in the atmospheres of S-type stars via its A-X and E-X electronic transitions near 1 lm [5], suggesting it may be detectable in circumstellar ejecta.…”