Synthesis, Structure, and Reactivity of Monomeric Titanocene Sulfido and Disulfide Complexes. Reaction of H₂ with a Terminal MS Bond

Abstract

The catalytic desulfurization of some organosulfur compounds has been proposed to proceed through an intermediate containing a metal-sulfur multiple bond which reacts with H 2 . 1-5 However, the activation of H 2 by a terminal MdS bond has not been observed in a discrete homogenous system. 6 In this communication, we report the synthesis of the terminal decamethyltitanocene sulfido complex Cp* 2 Ti(S)py (1, py ) pyridine) and its reactivity toward H-H and H-Si bonds. We also report the synthesis of the corresponding disulfide complex Cp* 2 Ti-(S 2 ) (2) and describe its reactivity toward dihydrogen.The decamethyltitanocene ethylene complex Cp* 2 Ti-(CH 2 CH 2 ) 7 (3) is a useful starting material for the synthesis of titanocene oxo, 8 imido, 9 and diazoalkane 10 complexes. This compound is also an excellent synthon for 1. Addition of a suspension of S 8 ( 1 / 8 equiv) to a toluene solution of 3 and py (5 equiv) results in an immediate color change from green to red. Subsequent reduction of the solvent volume, addition of pentane, and cooling to -40°C produce red crystals of 1 in 76% yield. Alternatively, 1 can be synthesized by addition of H 2 S (1 equiv) to a cold solution of 3 and py in THF, although in this case the product is isolated in much lower (ca. 30%) yields. The structure of 1 has been determined by X-ray diffraction; an ORTEP diagram is shown in Figure 1. The Ti-S bond length of 2.217(1) Å is longer than that found for other terminal titanium sulfido bonds 11-13 and is slightly longer than the value predicted for [Cp 2 TiS] using ab initio methods. 14,15 The geometry about the titanium center is very similar to that found in the analogous oxo compound, 8 although the Ti-N bond length is slightly longer (2.245(3) vs 2.215(4) Å) and the E-Ti-N bond angle is slightly wider (93.91(7)°vs 90.8(1)°) in the sulfido complex. At room temperature, the 300 MHz 1 H NMR spectrum shows a sharp Cp* resonance and two broadened peaks assigned to the meta and para pyridine proton resonances; the ortho proton resonances are broadened into the baseline. The broad pyridine resonances indicate that the pyridine ligand is dissociating reversibly from the metal center on the NMR time scale.Placing a degassed toluene-d 8 solution of 1 under H 2 (1 atm) results in a color change from red to yellow. The room temperature 300 MHz 1 H NMR spectrum of the yellow solution shows only a new Cp* resonance and peaks assignable to free py. Attempts to isolate the reaction product by removal of solvent from the yellow solution have resulted only in recovery of 1, indicating that the reaction is readily reversible. 16,17 However, cooling the solution to 273 K results in the decoalescence of resonances assignable to free py, free H 2 , and the hydride and hydrosulfido protons of Cp* 2 Ti(SH)H (4) (Scheme 1). 18 The 2D EXSY 1 H NMR spectrum 19 of this solution at 253 K ( Figure 2) shows that exchange is occurring between the H 2 , hydride, and hydrosulfido protons. Interestingly, the cross peaks between the hydride and hydrosulfido resona...

Catalytic Processes Involving Dihydrogen Complexes and Other Sigma-bond Complexes

“…The titanium system represents the first example of H 2 addition to a nonbridging disulfide complex [114]. An undetected H 2 complex may explain NMR evidence for H/H*-atom exchange on Ti, which also involves the protons in dissolved H 2 gas.…”

“…H 2 also readily reacts with a select few organometallic sulfides to give SH complexes that can show exchange behavior (scheme 16) [113][114][115][116].…”

η6‐Arene‐Zirconium‐PNP‐Pincer Complexes: Mechanism of Their Hydrogenolytic Formation and Their Reactivity as Zirconium(II) Synthons

“…Mindiola et al recently characterizedt he natureo ft heir (PNP)Ti(h 2 -ethylene) species as amaskedT i II reagent, [61][62][63] by reaction with two-electron oxidants, analogous to earlier work on [(h 5 -Cp*) 2 Ti(h 2 -C 2 H 4 )] by Bergman and Andersen. [96][97][98][99][100] Given that complexes 2 iPr Cl and 2 Ph I were precursors for Zr II species discussed in the previous section, it was of interestwhether reactions with potentialZ r =Nb ond-formingt wo-electron oxidants, would lead to the corresponding Zr IV species.…”

Role of single-site catalysts in the hydrogenation of thiophenes: from models systems to effective HDS catalysts

“…This has been attributed to the high stability of S-(M) n (n > 1) moieties towards the elimination of S as H 2 S. Even greater thermal and chemical stability seem to feature M@S moieties which may form along the desulfurization pathway (indeed, only one example of hydrogenation of M@S to M(H)SH in a metal complex has been reported so far [46] …”