Abstract
The reaction of 3,5-di-2-pyridyl-1,2,4-triazole with excess Al(CH3)3 and Ga(CH3)3 afforded (3,5-di-2-pyridyl-1,2,4-triazolate)Al(CH3)2•3Al(CH3)3 (1) and (3,5-di-2-pyridyl-1,2,4-triazolate) Ga(CH3)2•3Ga(CH3)3 (2) respectively. 1 and 2 reacted with oxygen gas to produce (CH3)2M(µ-3,5-di-2-pyridyl-1,2,4-triazolate)(µ-OCH3)M(CH3)2 (M = Al, 3; M = Ga, 4). 3 and 4 contain the non-bulky dimethylalumino moiety, yet they are indefinitely stable in the presence of oxygen gas. This increased stability towards oxygen is due to ancillary 2-pyridyl groups bonding to the metal centers producing a pseudo-trigonal pyramidal Al and Ga environments. This environment blocks oxygen from further inserting into the M–C bond. The Al–N(pyridine) and Ga–N(pyridine) bonds reported herein are extremely elongated yet inactive towards dissociation due to the chelate effect.
Highlights
[8] These complexes readily reacted with air to produce (CH3)2M(m-3,5-di-2-pyridyl-1,2,4-triazolate)(mOCH3)M(CH3)2 (M = Al, 3; M = Ga, 4). 3 and 4 contain a nonbulky dimethylalumino moiety, yet they are indefinitely stable in the presence of oxygen gas
Triazole with excess Al(CH3)3 and Ga(CH3)3 in toluene under an atmosphere of argon (Figure 1). 3 and 4 comprise an oxidation resistant [M(CH3)2]+ moiety that is protected by pendant pyridyl groups resulting in a pseudo-trigonal bipyramidal geometry around M with the longest M–N(pyridine) reported bond distances to date. 1–4 have been characterized by spectral analysis and Xray measurements
The triazolato cores, pyridyl groups, metal atoms, and methoxy groups all lie within the same plane
Summary
[7] Compounds of the general formula [R2AlL]2, where L = pyrazolate, readily react with O2 to produce an alkoxide when the alkyl group R is non-bulky, such as R = Me, Et; whereas they are stable towards reaction with O2 when R is bulky, such as R = tBu. There are no examples of a non-bulky alkyl group bonded to a tetrahedral group 13 metal that can resist oxidation to alkoxide or peroxide upon exposure to oxygen gas. I became interested in pursuing complexes that bear resemblance to methylalumoxane (MAO), a common co-catalyst. This rekindled my interest in the above compounds and I set out to understand the reaction further by elucidating its mechanism. I hereby report the mechanism and the insight this reaction brings into the corrosion protection of aluminum
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