Chiral Br酶nsted Acid Catalysts. Activation of Methyl 3,3,3-Trifluoropyruvate by Hydroxymethylpyridine-Containing Half-Sandwich Complexes

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• 作者：Daniel Carmona ; Pilar Lamata ; Antonio S谩nchez ; Pilar Pardo ; Ricardo Rodr铆guez ; Paola Ram铆rez ; Fernando J. Lahoz ; Pilar Garc铆a-Ordu帽a ; Luis A. Oro
• 刊名：Organometallics
• 出版年：2014
• 出版时间：August 11, 2014
• 年：2014
• 卷：33
• 期：15
• 页码：4016-4026
• 全文大小：601K
• ISSN：1520-6041

文摘

The coordinated OH group in cationic complexes [(畏ⁿ-ring)M(NOH)(Solv)][SbF₆] and [(畏ⁿ-ring)M(NOH){(R)-P1}][SbF₆]₂ ((畏ⁿ-ring)M = (畏⁵-C₅Me₅)Rh, (畏⁵-C₅Me₅)Ir, (畏⁶-p-MeC₆H₄iPr)Ru; NOH = hydroxypyridine ligand; (R)-P1 = (R)-monophos) is deprotonated by Na₂CO₃, rendering bi- or mononuclear compounds of formulas [{(畏ⁿ-ring)M(魏²N,O-渭-O-NO}₂][SbF₆]₂ and [(畏ⁿ-ring)M(NO){(R)-P1}][SbF₆], respectively. The complexes have been characterized by analytical and spectroscopic means, including the determination of the crystal structures of [{(畏ⁿ-ring)M(魏²N,O-渭-O-NO}₂][SbF₆]₂ (NOH = NOH-1, (畏ⁿ-ring)M = (畏⁵-C₅Me₅)Rh, 8a; (畏⁶-p-MeC₆H₄iPr)Ru, 8c) and [(畏⁵-C₅Me₅)Ir(NO){(R)-P1}][SbF₆] (NOH = (R)-NOH-2; (R)-11b) by X-ray diffractometric methods. In complexes [(畏ⁿ-ring)M(NOH)(P*)][SbF₆]₂ (P* = chiral phosphoramidite ligand) the proton of the coordinated hydroxypyridine ligand is able to activate the carbonyl group of methyl 3,3,3-trifluoropyruvate toward the Friedel鈥揅rafts addition of indoles. In most cases, quantitative conversion is achieved in a few minutes, at 鈭?0 掳C, with an ee of up to 82%. NMR data support the activation of the pyruvate by interaction between its carbonyl oxygen and the OH group of the coordinated hydroxymethylpyridine. Therefore, the metallic complexes act as Lewis acid assisted Br酶nsted acid catalysts.