García-de-Jesus OJ, Mondragón-Díaz A, Donnadieu B, Muñoz-Hernández MÁ. Tuning of Cu-Al Interactions in Complexes Derived from Tris(pyridonyl-6-methyl)aluminum Metalloligands.
Inorg Chem 2023;
62:2518-2529. [PMID:
36706381 DOI:
10.1021/acs.inorgchem.2c02273]
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Abstract
A series of bioinspired polar atrane Cu-Al complexes were studied with a combined experimental and computational approach to assess the range and nature of Cu-Al interactions in these novel species. The aluminum metalloligand [Na{Me2Al(OPy-6-Me)2}] (2) was furnished in excellent yield (92%) from the nucleophilic attack of Na(OPy-6-Me) to AlMe3 and the subsequent alkane elimination reaction with 6-methyl-2-hydroxypyridine. At the same time, the metalloligand [Al(OPy-6-Me)3] (3) was isolated in an also excellent yield (95%) via alkane elimination of AlMe3 with 6-methyl-2-hydroxypyridine. The zwitterionic Cu-Al atranes [Cu{MeAl(OPy-6-Me)3}] (5Me) and [Cu{MesAl(OPy-6-Me)3}] (5Mes) were isolated (73 and 97% yields) from metalloligands 2 and 3, respectively. [(Cu{Al(OPy-6-Me)4})2(μ-Cu)]+ ([6+][B(ArCF3)4]) was isolated via a reaction that involves alkane elimination and redistribution reacting from 5Me with [H(OEt2)2][B(ArCF3)4] in benzene solution. Alkane elimination in benzene of either 5Me or 5Mes with [HNEt3][B(ArCF3)4] renders [Cu{(Et3N)Al(OPy-6-Me)3}]+ (Et3N-5+). The Lewis base-free cationic complex [Cu{Al(OPy-6-Me)3}]+ (5+) was isolated in 68% yield upon reacting 3 with [Cu(COD)2][B(ArCF3)4] in benzene. Metalloligands and complexes were fully characterized with an array of spectroscopic and analytical techniques that include multinuclear NMR, ATR-IR, ESI-spectrometry, combustion microanalysis, cyclic voltammetry (CV), and, whenever feasible, SCXRD. X-ray and DFT parameters indicate that the strength of the Cu→Al transannular interaction follows the trend 5+ > Et3N-5+ > [6+][B(ArCF3)4], 5Me, and 5Mes in a smooth transition from zwitterionic species where the Cu-Al interaction is nonexistent to moderate Cu-Al Z-type interactions. CV, in conjunction with DFT calculations of Et3N-5+ and 5+, hint at the generation in the electrochemical cell of the radical species 5rad at -1.82 V and the anionic complex 5- at -2.32 V vs Fc/Fc+, respectively. The proposed species 5rad exhibits 2-center/1-electron (2c/1e) σ bonding whereas 5- a 2-center/2-electron (2c/2e) bond.
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