Deuteron magnetic resonance study of the mechanism of methyl group exchange between tetramethyltitanium and trimethylaluminium

The exchange of methyl groups between tetramethyltitanium and trimethylaluminium has been studied by the direct observation of a new resonance line in the ²D NMR spectrum of the reaction mixture containing perdeuterated and undeuterated organometallic compounds.The kinetics and mechanism of the exchange reaction are influenced by the ethyl ether concentration in a hexane solution of the tetramethyltitanium compound. At a molar ratio TiMe₄/Et₂0 > 1 rapid exchange occurs between unsolvated metal alkyls. Tetramethyltitanium etherate reacts with trimethylaluminium in two steps, an initial fast complexation to Me₃Ti AlMe₄] which accounts for the transfer of a single methyl group from the titanium to the aluminium atom and a subsequent slow reverse process which leads to the transfer of methyl groups from the aluminium to the titanium atom and which results ultimately in a random equilibrium distribution of the labelled methyl groups amongst both metal atoms.Mixing the etherates of both titanium and aluminium methyl compounds led to the appearance of an extra signal downfield (τ 5.6 ppm) which is apparently due to the methyl resonance of the species TiMe₃]⁺ in the solvent-separated ion-pair form of the complex TiMe₃]⁺ AlMe₄]^?.