The Influence of Coordinating Solvents on the Thermal Decomposition of Methyl Titanium Trichloride

Abstract

The mechanism of decomposition of CH3TiCI3 in coordinating solvents is shown not to involve free radicals in some cases. An analysis of published work on the decomposition of titanium alkyls suggests mechanisms of decomposition similar to those postulated for alkyls of other transition metals.On demontre que dans certain cas le mecanisme de decomposition du CH3TiC13 dans des solvants coordinants n'implique pas de radicaux libres. Une analyse des resultats publies sur la decomposition des alkyl titanium suggere que leurs mkcanismes de dCcomposition sont similaires a ceux des derives alkyles des autres metaux de transition.[Traduit par le journal]Can. J . Chern.. 51. 1083 (1973) A free radical mechanism of thermal &corn-from Stohler Inc., and from Wilmad Co.Inc.,respectively, position is widely accepted for many alkyl -and were used as received. Non-deuterated solvents were purchased in reagent grade and were distilled under transition metal compounds 2), Particularly the middle cut being used. Both ethers were[ those involving methyl groups. In the particular first refluxed over sodium. case of CH3TiCI,, there is conclusive evidence (3) that free radicals do not form in non-co-Preparatiof2 of CH3TiC13All steps of the preparation were carried out within a ordinating solvents but it has become accepted box of dry nitrogen.(4) that a free radical mechanism is predominant (cH,),~, (3.1 x m01) was added slowiy to a in coordinating solvents. Such a mechanism was solution of 6.2 x mol of TiCI4 in 5 ml of CC13F at originally proposed (5) on the basis of mass about 0°C. After a few minutes shaking as the solution balance considerations and of the relatively fast warmed to room temperature, the precipitated zinc chloride was filtered off. Three 1 ml amounts of CC13F decompositions in coordinating solvents, and it were used to wash remaining CH3TiC13 solution from the was given substantial support by the observation preparation vessel and the filter.(6) that the decomposition kinetics are firstUsing ungreased ground glass joints to prevent reacorder, and that CH,D is among the products, tion, a vacuum trap-to-trap distillation at -35" separated the CH3TiC13 from the more volatile CC13F. The purple when the is carried O u t in a mixed crystals were then dissolved in the working solvent o r solvent tetrahydrof~lran and perdeuterotoluene. transferred directly to the reaction vessel. Precipitation The observation of unambiguous first order techniques of the sort usually employed (3,4,7) invariably kinetics is consistent with the postulate that the result in the occlusion of some solvent (even heptane) in the CH3TiC13 crystals and were therefore unsatisfactory breaking Of the bond for the work in this paper. Two or three distillations are is the rate determining step. Moreover, the exis-required where complete solvent removal is obligatory. tence of CH3D among the products tended to confirm that a radical had formed, capable of Deco~71positiot1 Strldies and ~esrrlts attacking toluene-d, molecules were, A series of decomposi...

1,n-Dicarbanionic Titanium Intermediates from Monocarbanionic Organometallics and Their Application in Organic Synthesis

“…Crystalline PhTi(O i -Pr) 3 was the first isolated and fully characterized organotitanium compound. , Methyl- and other monoalkyltitanium derivatives are also reasonably stable, but di-, tri-, and tetraalkylated derivatives all appear to be considerably less stable. Quantitative data were obtained for the thermal decompositions of methyl-, − benzyl-, − and neopentyltitanium(IV) derivatives ,− to evidence that free radicals are not formed in these decomposition reactions, at least not in noncoordinating solvents. The relatively lower stability of the organotitanium compounds is definitely not connected with a particular weakness of the carbon−titanium σ-bonds (in fact, these bond energies usually exceed 60 kcal mol -1 ) but rather with the readiness of titanium to provide its low-lying empty d-orbitals for so-called agostic interactions with neighboring σ-bonds. ,− In the trichloro(methyl)titanium ethylenediphosphine chelate 1 , R = Me, the methyl group displays a pronounced distortion with a Ti−C−H angle of 70(2)°, , and this phenomenon has been explained with an agostic interaction between the titanium atom and the C α −H bond …”

“…32,33 Methyl-and other monoalkyltitanium derivatives are also reasonably stable, but di-, tri-, and tetraalkylated derivatives all appear to be considerably less stable. Quantitative data were obtained for the thermal decompositions of methyl-, [34][35][36][37][38][39][40] benzyl-, [41][42][43] and neopentyltitanium(IV) derivatives 41,[44][45][46] to evidence that free radicals are not formed in these decomposition reactions, at least not in noncoordinating solvents. The relatively lower stability of the organotitanium compounds 47 is definitely not connected with a particular weakness of the carbontitanium σ-bonds (in fact, these bond energies usually exceed 60 kcal mol -1 ) 48 but rather with the readiness of titanium to provide its low-lying empty d-orbitals for so-called agostic interactions 49 with neighboring σ-bonds.…”

Metal .sigma.-hydrocarbyls, MRn. Stoichiometry, structures, stabilities, and thermal decomposition pathways

“…230 Reaction may be precluded by use of ethers without /3-hydrogens, e.g., Ph20. 235 Other reactions that fall in this category are shown in eq 42, 258 43,234 44,103 45,91 and 46.259 These involve attack at a coordinated anionic ligand, which may be a hydrocarbyl group.…”