Aerobic Oxidation Reactions Catalyzed by Vanadium Complexes of Bis(Phenolate) Ligands

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• 作者：Guoqi Zhang ; Brian L. Scott ; Ruilian Wu ; L. A. 鈥淧ete鈥?Silks ; Susan K. Hanson
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：July 2, 2012
• 年：2012
• 卷：51
• 期：13
• 页码：7354-7361
• 全文大小：412K
• 年卷期：v.51,no.13(July 2, 2012)
• ISSN：1520-510X

文摘

Vanadium(V) complexes of the tridentate bis(phenolate)pyridine ligand H₂BPP (H₂BPP = 2,6-(HOC₆H₂-2,4-^tBu₂)₂NC₅H₃) and the bis(phenolate)amine ligand H₂BPA (H₂BPA = N,N-bis(2-hydroxy-4,5-dimethylbenzyl)propylamine) have been synthesized and characterized. The ability of the complexes to mediate the oxidative C鈥揅 bond cleavage of pinacol was tested. Reaction of the complex (BPP)V^V(O)(OⁱPr) (4) with pinacol afforded the monomeric vanadium(IV) product (BPP)V^IV(O)(HOⁱPr) (6) and acetone. Vanadium(IV) complex 6 was oxidized rapidly by air at room temperature in the presence of NEt₃, yielding the vanadium(V) cis-dioxo complex [(BPP)V^V(O)₂]HNEt₃. Complex (BPA)V^V(O)(OⁱPr) (5) reacted with pinacol at room temperature, to afford acetone and the vanadium(IV) dimer [(BPA)V^IV(O)(HOⁱPr)]₂. Complexes 4 and 5 were evaluated as catalysts for the aerobic oxidation of 4-methoxybenzyl alcohol and arylglycerol 尾-aryl ether lignin model compounds. Although both 4 and 5 catalyzed the aerobic oxidation of 4-methoxybenzyl alcohol, complex 4 was found to be a more active and robust catalyst for oxidation of the lignin model compounds. The catalytic activities and selectivities of the bis(phenolate) complexes are compared to previously reported catalysts.