Theoretical Studies on the Decomposition Mechanism of Tetraalkyl Titanium Complexes

Abstract

Unimolecular and bimolecular methane eliminations of TiMe4 have been studied using ab initio molecular orbital theory. Geometry optimizations were performed with the 3-21G and HW3 (equivalent to the 6−31G*) basis sets. The energies were further evaluated with the MP2/HW3 calculations. We predict a high activation energy for unimolecular methane elimination but a low activation energy for bimolecular methane elimination. For Ti(CH2CMe3)4, neopentane elimination through α- and γ-hydrogen abstractions has been studied with the 3-21G basis set. We predict an intrinsic preference for α-hydrogen abstraction over γ-hydrogen abstraction. This preference is enhanced by the bulkiness of the alkyl ligands.

Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

“…These observations are consistent with a four-center transition state A (Scheme 6 (15) reactions are rare that convert a metalecarbon single bond to a double bond and then to a triple bond [13]. At the time of our studies of Ta(CH 2 SiMe 3 ) 5 (19), the pathway in the formation of the archetypical Schrock alkyl alkylidene complex (Me 3 CCH 2 ) 3 Ta]CHCMe 3 (5a) was not clear.…”

“…Our initial studies of Cp-free alkyl alkylidene complexes were largely a result of an attempt to confirm the formation of (Me 3 SiCH 2 ) 4 Ta 2 (m-CSiMe 3 ) 2 (15) in the preparation of (Me 3 SiCH 2 ) 2 -Ta(]CHSiMe 3 )[Si(SiMe 3 ) 3 ] (3b) (Schemes 2 and 4). Complex 15 had been prepared by Wilkinson and Mowat in the early 1970s [10].…”

“…The peaks in the 1 H and 13 C NMR spectra of 19 disappeared with time, indicating that it was unstable. The alkyl complex 19 first converted to the alkylidene (Me 3 SiCH 2 ) 3 Ta]CHSiMe 3 (5b) and then to the alkylidyne (Me 3 SiCH 2 ) 4 Ta(m-CSiMe 3 ) 2 (15) through two consecutive a-H abstraction steps (Scheme 5). Additional work showed that 19 could be more easily prepared from (Me 3 SiCH 2 ) 3 TaCl 2 (13b) and LiCH 2 SiMe 3 (Scheme 5).…”

Equilibrium analysis of zirconium carbide CVD growth

“…For example, it is reported that a temperature of $300 1C is required to initiate the a-hydrogen abstraction (reaction (1)), which is an important step for neopentane elimination leading to ZrQC bond formation [26]. Consistent with this kinetic limitation, growth of ZrC using ZrNp 4 in AA-MOCVD at less than 400 1C did not result in film growth [20].…”

Growth of ZrC thin films by aerosol-assisted MOCVD

“…Thus, other decomposition processes are more likely to compete with Zr-C homolysis in ZrNp 4. Neopentyl groups are known to undergo C-H activation at the a and g positions as well as C-C bond cleavage within the ligand [38,39]. These processes within the neopentyl ligand would provide pathways for carbon incorporation into the films.…”