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Mechanism of Generation of closo-Decaborato Amidrazones. Intramolecular Non-covalent B–H•••π(Ph) Interaction Determines Stabilization of the Configuration around the Amidrazone C=N Bond

Abstract

Three types of N(H)-nucleophiles, viz. hydrazine, acetyl hydrazide, and a set of hydrazones, were used to study the nucleophilic addition to the C≡N group of the 2-propanenitrilium closo-decaborate cluster (Ph3PCH2Ph)[B10H9NCEt], giving N-closo-decaborato amidrazones. A systematic mechanistic study of the nucleophilic addition is provided and included detailed synthetic, crystallographic, computational and kinetic work. As a result, two possible mechanisms have been proposed, which consist of firstly a consecutive incorporation of two Nu(H) nucleophiles, with the second responsible for a subsequent rapid proton exchange. The second possible mechanism assumes a pre-formation of a dinuclear [Nu(H)]2 species which subsequently proceeds with the nucleophilic attack on the boron cluster. The activation parameters for hydrazones indicate a small dependence on bond formation [ΔH≠ = 6.8–15 kJ⋅mol–1], but significantly negative entropies of activation [ΔS≠ ranges from –139 to –164 J⋅K–1⋅mol–1] with the latter contributing some 70–80% of the total Gibbs free energy of activation, ΔG≠. In the X-ray structure of (Z)-(Ph3PCH2Ph)[B10H9N(H)=C(Et)NHN=CPh2], very rare intramolecular non-covalent interactions B–H•••π(Ph) were detected and studied by DFT calculations (M06-2X/6-311++G** level of theory) and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method). Estimated strength of these non-covalent interactions is 0.8–1.4 kcal/mol.

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Publication details

The article was received on 01 Mar 2018, accepted on 11 Apr 2018 and first published on 11 Apr 2018


Article type: Paper
DOI: 10.1039/C8NJ01018H
Citation: New J. Chem., 2018, Accepted Manuscript
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    Mechanism of Generation of closo-Decaborato Amidrazones. Intramolecular Non-covalent B–H•••π(Ph) Interaction Determines Stabilization of the Configuration around the Amidrazone C=N Bond

    V. K. Burianova, D. S. Bolotin, A. S. Mikherdov, A. S. Novikov, P. Mokolokolo, A. Roodt, V. P. Boyarskiy, D. Dar'in, M. Krasavin, V. V. Suslonov, A. P. Zhdanov, K. Yu. Zhizhin and N. T. Kuznetsov, New J. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C8NJ01018H

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