Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

Abstract

Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1CCR2 into its Ti–H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1CCHR2)] (2a–e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti–H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a–4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RCC)2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a–2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1CCHR2)] 3a–3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a–3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d 8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a–4c, 5a, 6b, and 7.

Probing the coordination environment of Ti3+ions coordinated to nitrogen-containing Lewis bases

“…The violet a-polymorph of TiCl 3 (a-TiCl 3 ) was dissolved in anhydrous 1-methyl imidazole, while the green TiCl 3 (Py) 3 complex was dissolved in pyridine. The violet a-polymorph of TiCl 3 (a-TiCl 3 ) was dissolved in anhydrous 1-methyl imidazole, while the green TiCl 3 (Py) 3 complex was dissolved in pyridine.…”

“…5, the Q-band HYSCORE spectra for the solid state sample and for the TiCl 3 (Py) 3 complex dissolved in pyridine are reported along with the corresponding computer simulations. In Fig.…”

“…5 In order to interpret the complex spectra associated with the heterogeneous catalysts, however, reliable reference data are needed, which can be obtained from model systems. In an effort to extend the set of reference data to nitrogen-based ligands, we studied the solid-state compound TiCl 3 (Py) 3 and frozen solutions of Ti 3+ chloride dissolved in 1-methyl imidazole and pyridine. In an effort to extend the set of reference data to nitrogen-based ligands, we studied the solid-state compound TiCl 3 (Py) 3 and frozen solutions of Ti 3+ chloride dissolved in 1-methyl imidazole and pyridine.…”

“…Titanium(III) compounds play an important role in both homogeneous and heterogeneous catalysis in the fields of olefin polymerization 1,2 and hydrogenation 3 or as initiators in radical reactions. 4 Catalytically active species are characterized by specific oxidation states and coordination geometries, which ultimately determine the activity and (stereo)selectivity of the catalysts.…”

Molecular Hydrogen‐Induced Carbon Chain Rearrangement in Cyclopentadienyl‐Tethered Titanium(III) Permethyltitanocene Complexes

“…The EI–MS spectra showed always the molecular ions as the base peaks and the tether elimination yielding abundant [ 1 ] + . EPR spectra showed single signals in the range g iso = 1.964–1.959 and Δ H ≈ 11–15 G. Electronic absorption spectra displayed two absorption bands of 1a 1 →2a 1 and 1a 1 →b 1 transitions in the 450–600 nm region, which were only slightly different from data for compounds 2 , alkenyltitanocenes Cp* 2 Ti(CR 1 =CHR 2 ) [ref .…”