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Reactions of Trimethylaluminium: Modelling the Chemical Degradation of Synthetic Lubricants

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Slaughter, Jonathan  ORCID logo
Peel, AJ 
Wheatley, AEH 


In investigating and seeking to mimic the reactivity of trimethylaluminium (TMA) with synthetic, ester-based lubricating oils, the reaction of methyl propionate 1 was explored with 1, 2 and 3 equivalents of the organoaluminium reagent. Spectroscopic analysis points to the formation of the adduct 1 (TMA) accompanied only by the low level 1:1 production of Me2AlOCEtMe2 2 and Me2AlOMe 3 when an equimolar amount of TMA is applied. The deployment of excess TMA favours reaction to give 2 and 3 over 1(TMA) adduct formation and spectroscopy reveals that in hydrocarbon solution substitution product 2 traps unreacted TMA to yield 2(TMA). The 1H 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 Me4Al22-Me)(μ2-OCEtMe2 ). In the presence of 3, 2(TMA) undergoes thermally induced exchange to yield Me4Al22-OMe)(μ2-OCEtMe2) 4 and TMA. The reaction of methyl phenylacetate 5 with TMA allows isolation of the crystalline product Me2AlOCBnMe2 (TMA) 6(TMA), which allows the first observation of the Me Al22-Me)(μ2-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 from 6(TMA) by the introduction of Et2O has yielded 6, which exists as a dimer.



esters, NMR spectroscopy, nucleophilic addition, solid-state structures, trimethylaluminium

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Chemistry - A European Journal

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Engineering and Physical Sciences Research Council (EP/K039520/1)
This work was supported by Cambridge Refrigeration Technology (J.S.). The U.K. EPSRC are acknowledged for grant EP/J500380/1 (A.J.P.).
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