Reactions of Trimethylaluminium: Modelling the Chemical Degradation of Synthetic Lubricants. Issue 1 (5th December 2016) - Slaughter, Jonathan
Abstract: In investigating and seeking to mimic the reactivity of trimethylaluminium (TMA) with synthetic, ester‐based lubricating oils, the reaction of methyl propionate1 was explored with 1, 2 and 3 equivalents of the organoaluminium reagent. Spectroscopic analysis points to the formation of the adduct1 (TMA) accompanied only by the low level 1:1 production of Me2 AlOCEtMe2 2 and Me2 AlOMe3 when an equimolar amount of TMA is applied. The deployment of excess TMA favours reaction to give2 and3 over1 (TMA) adduct formation and spectroscopy reveals that in hydrocarbon solution substitution product2 traps unreacted TMA to yield2 (TMA). The 1 H NMR spectroscopic observation of two Al−Me signals not attributable to free TMA and in the ratio 1:4 suggests the formation of a previously only postulated, symmetrical metallacycle in Me4 Al2 (μ 2 ‐Me)(μ 2 ‐OCEtMe2 ). In the presence of3, 2 (TMA) undergoes thermally induced exchange to yield Me4 Al2 (μ 2 ‐OMe)(μ 2 ‐OCEtMe2 )4 and TMA. The reaction of methyl phenylacetate5 with TMA allows isolation of the crystalline product Me2 AlOCBnMe2 (TMA)6 (TMA), which allows the first observation of the Me4 Al2 (μ 2 ‐Me)(μ 2 ‐OR) motif in the solid state. Distances of 2.133(3) Å (Al−Mebridging ) and 1.951 Å (mean Al−Meterminal ) are recorded. The abstraction of TMA from6 (TMA) by the introduction of Et2 O has yielded6, which exists as a dimer. Abstract : Attack of the alkylaluminiums : The reaction of trimethylaluminium (TMA) with ester mimics of synthetic lubricants has been investigated with results pointing to adduct formation followed by reaction with two further equivalents of TMA and the trapping of intermediate Me2 AlOCRMe2 (TMA) en route to Me2 AlOCRMe2 (Me2 AlOMe), each of which demonstrate a symmetrical OAl2 X (X=C, O) metallacycle.