This paper describes the reactivity of the base-free titanium imido complex Cp* 2 TidNPh (1) (Cp* ) pentamethylcyclopentadienyl) toward alkenes and alkynes. Complex 1 reacts with ethylene and acetylene to generate the azametallacycles Cp* 2 Ti(N(Ph)CH 2 CH 2 ) (2) and Cp* 2 Ti(N(Ph)CHdCH) (3), respectively. In the case of ethylene, the cycloaddition is readily reversible, and 2 was characterized spectroscopically under an ethylene atmosphere. We have also examined the reactivity of 1 toward phenyl-and trimethylsilylacetylene and have found that 1 activates the alkynyl C-H bond to give anilido-acetylide complexes Cp* 2 Ti(N(Ph)H)Ct CR (6, R ) Ph; 7, R ) SiMe 3 ). This reaction proceeds without observable intermediate metallacyclobutene complexes such as those observed previously for the reaction of the related oxo complex Cp* 2 Ti(O)pyr (pyr ) pyridine) with terminal alkynes. Thermolysis of azametallacyclobutene 3 results in formation of the novel ring-activated complex Cp*(η 5 ,η 1 -C 5 Me 4 CH 2 CHdCH)TiN(Ph)H (5).

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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.

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...

Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium dichloride, in the presence of methylaluminoxane (MAO), are catalyst precursors for the synthesis of elastomeric polypropylene. The nature of the cocatalyst is shown to have a significant influence on the productivity and stereoselectivity of these metallocenes. Propylene polymerizations in liquid propylene in the presence of bis(2-phenylindenyl)zirconium dimethyl (5) activated by three different types of methyaluminoxane, trityl tetrakis(pentafluorophenyl)borate (1), dimethylanilinium tetrakis(pentafluorophenyl)borate (2), or tris(pentafluorophenyl)borane (3), revealed a significant influence of activator on the polymerization behavior of these catalysts: both the productivity and stereoselectivity of the catalyst systems were highest with MAO and lowest with the borane 3 (MAO > 1 ≈ 2 . 3). Catalysts derived from the borane 3 yielded amorphous atactic polypropylenes under conditions where those from cocatalysts MAO, 1, or 2 yielded semicrystalline, low-tacticity polypropylenes. The type of MAO also influences the stereoselectivity: MAOs containing isobutylaluminum groups yielded higher tacticity polypropylenes than those with only methylaluminum groups. Solution polymerizations in solvents of varying polarities revealed that the polarity of the solvent influenced the productivities but had little influence on the stereoselectivity.