Regiocontrolled One-Step Synthesis of 3,3′-Disubstituted 2,2′-Bipyridine Ligands by Cobalt(I)-Catalyzed Cyclotrimerization
- 3 December 2001
- journal article
- Published by Wiley in Chemistry – A European Journal
- Vol. 7 (23), 5203-5213
- https://doi.org/10.1002/1521-3765(20011203)7:23<5203::aid-chem5203>3.0.co;2-r
Abstract
A one‐step, regioselective synthesis of annelated symmetric and asymmetric 3,3′‐disubstituted 2,2′‐bipyridines by cobalt(I)‐catalyzed [2+2+2] cycloadditions between 5‐hexynenitrile and 1,3‐diynes is described. In the symmetric case, the total regioselectivity of the first cycloaddition is ensured electronically by the conjugation of the triple bonds, and for aminomethylated diynes that of the second is ensured by the cobalt coordinating to the aminomethyl rather than to the hexynenitrile nitrogen. In the asymmetric case, the first cycloaddition took place chemoselectively, which in the case of bis(trimethylsilyl)‐1,3,5‐hexatriyne (viewed as a 1,3‐diyne) is explained by semiempirical calculation of LUMO coefficients. The copper(I) complex of 6 b, constituting the first reported complex of the form ML2 (L is a symmetric 3,3′‐disubstituted 2,2′‐bipyridine), has been prepared. It had UV/Vis and NMR spectra reflecting the 3‐substituent‐induced mutual torsion of the bipyridine rings in the cis conformation, as was confirmed by x‐ray diffractometric determination. The bipyridine 6 c forms the dinuclear complex [Cu2(6 c)2(CH3CN)2]2+ in the solid state. Se describe la síntesis regioselectiva en un solo paso de 2,2′‐bipiridinas 3,3′‐disustituidas, tanto simétrica como asimétricamente, mediante reacciones de cicloadición [2+2+2] catalizadas por CoI entre el 5‐hexinonitrilo y 1,3‐diinos. En el caso de los diinos simétricos, la regioselectividad en la primera cicloadición se debe al efecto electrónico causado por la conjugación de los triples enlaces mientras que la regioselectividad en la segunda cicloadición, en el caso del diino aminometilado, es debida a la coordinación del nitrógeno del aminometilo al cobalto en vez del resto nitrilo. Con los diinos asimétricos, se observa que la primera cicloadición es quimioselectiva y para el caso del bis(trimetilsilil)‐1,3,5‐hexatriino se puede explicar mediante cálculos semiempíricos de los coeficientes LUMO. Se han preparado por primera vez complejos de CuI con estructura ML2 en los que sus datos espectrales de UV/Vis y RMN reflejan la torsión de los anillos de bipiridina causada por la presencia de sustituyentes en posiciones 3 y 3′. Se pudo confirmar en algún caso este efecto mediante el espectro de difracción de rayos X. En el caso de la bipiridina 6 c se obtuvo el complejo dinuclear [Cu2(6 c)2(CH3CN)2]2+ en forma cristalina.Keywords
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