Aluminium alkyl and aryloxide complexes of pyrazine and bipyridines: synthesis and structure?

Dalton Transactions Pub Date: 2004-10-07 DOI: 10.1039/B410662H

Abstract

The reaction of AlMe3 and [(tBu)2Al(μ-OPh)]2 with pyrazine (pyz), 4,4′-bipyridine (4-4′-bipy), 1,2-bis(4-pyridyl)ethane (bpetha) and 1,2-bis(4-pyridyl)ethylene (bpethe) yields (Me3Al)2(μ-pyz) (1), (Me3Al)2(μ-4,4′-bipy) (2), (Me3Al)2(μ-bpetha) (3), (Me3Al)2(μ-bipethe) (4), Al(tBu)2(OPh)(pyz) (5), [(tBu)2Al(OPh)]2(μ-4,4-bipy) (6a), [(tBu)2Al(OPh)]2(μ-bpetha) (7a), [(tBu)2Al(OPh)]2(μ-bipethe) (8a). Compounds 1–4, 6a and 7a have been confirmed by X-ray crystallography. In solution compounds 1–4 undergo a rapid ligand-dissociation equilibrium resulting in a time-average spectrum in the 1H NMR. In contrast, the solution equilibria for compounds 5–8a are sufficiently slow such that the mono-aluminium compounds may be observed by 1H NMR spectroscopy: Al(tBu)2(OPh)(4,4-bipy) (6b), Al(tBu)2(OPh)(bpetha) (7b) and Al(tBu)2(OPh)(bpethe) (8b). The inability to isolate [(tBu)2Al(OPh)]2(μ-pyz) and the relative stability of each complex is discussed with respect to the steric interactions across the bridging ligand (L) and the electronic effect on one Lewis acid–base interaction by the second Lewis acid–base interaction on the same ligand.

Graphical abstract: Aluminium alkyl and aryloxide complexes of pyrazine and bipyridines: synthesis and structure
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