Coupling of Azomethine Ylides with Nitrilium Derivatives of closo-Decaborate Clusters: A Synthetic and Theoretical Study

Authors

  • Aleksey L. Mindich,

    1. Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
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  • Nadezhda A. Bokach,

    Corresponding author
    1. Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
    • Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
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  • Maxim L. Kuznetsov,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade Técnica de Lisboa, Avenida Rovisco Pais, 1049-001 Lisbon (Portugal)
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  • Matti Haukka,

    1. Department of Chemistry, University of Jyväskylä, P.O. Box 35, 40014 University of Jyväskylä (Finland)
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  • Andrey P. Zhdanov,

    1. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Pr., 119991 Moscow (Russian Federation)
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  • Konstantin Yu. Zhizhin,

    1. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Pr., 119991 Moscow (Russian Federation)
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  • Serguei A. Miltsov,

    1. Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
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  • Nikolay T. Kuznetsov,

    1. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Pr., 119991 Moscow (Russian Federation)
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  • Vadim Yu. Kukushkin

    Corresponding author
    1. Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
    2. Saint Petersburg State Forest Technical University, Institutskii per. 5, 194021 Saint Petersburg (Russian Federation)
    • Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation), Fax: (+7) 812-4286939
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Abstract

The azomethine ylides p-R3C5H4N+CHCOC6H4R2-p (3 a: R3=H, R2=H, X=Br; 3 b: R3=H, R2=Me, X=I; 3 c: R3=H, R2=OMe, X=I; 3 d: R3=H, R2=F, X=I; 3 e: R3=Me, R2=Me, X=Br) react with the nitrile functionality of the closo-decaborate clusters [Bun4N][B10H9(NCR1)] (1 a: R1=Me; 1 b: R1=Et; 1 c: R1=Ph) in a CH3NO2 solution under mild conditions (20–25 °C, 2 min) to afford selectively products of the nucleophilic addition (ca. quantitative yields based on NMR analysis in [D6]DMSO, 71–87 % yield of isolated products). These products are the borylated enamino ketones as the salts bearing exclusively a tetrabutylammonium cation [Bun4N][B10H9{NCR1=C(N+C5H4R3-p)COC6H4R2-p}] (4 ah,kn) or the mixed salts [Bun4N]1-x[p-R3C5H4N+CH2COC6H4R2-p]x[B10H9{NCR1=C(N+C5H4R3-p)COC6H4R2-p}] (4 i, 4 j, and 4 o). This reaction represents the first example of the selective nucleophilic addition of pyridinium azomethine ylides to the nitrile group and the first example of new C[BOND]C bond formation in the reaction of nitrilium derivatives of boron clusters with any nucleophiles so far tested. Compounds 4 ah,kn were characterized by ICP-MS, high resolution ESI-MS, molar conductivity, and IR, 1H, 13C{1H}, and 11B{1H} NMR spectroscopy. The structures of 4 a and 4 b were determined by a single-crystal X-ray analysis. Theoretical calculations at the DFT level allowed the interpretation of the observed reaction selectivity, which is driven mostly by thermodynamic rather than kinetic factors, and steric repulsion between the boron cluster and the azomethine ylide molecule plays a crucial role. The activation of the nitrile group upon binding to the boron cluster is explained in terms of the electrostatic arguments. The mechanisms of the nucleophilic addition and the hypothetical cycloaddition between the azomethine ylide and nitriles were investigated in detail.

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