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Molecules 2018, 23(11), 2942; https://doi.org/10.3390/molecules23112942

Reaction between Indazole and Pd-Bound Isocyanides—A Theoretical Mechanistic Study

1
Dipartimento di Scienze della Terra e del Mare, Università degli Studi di Palermo, Via Archirafi, 22, 90123 Palermo, Italy
2
Consorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sistemi Biologici (C.I.R.C.M.S.B.), Piazza Umberto I, 70121 Bari, Italy
3
Dipartimento di Scienze Chimiche, Università di Padova, via F. Marzolo 1, 35131 Padova, Italy
4
International Group on Organometallic Chemistry, Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab., 7/9, Saint Petersburg 199034, Russia
5
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
G.C. performed this work during his leave of absence period at the Dipartimento di Scienze Chimiche, Università di Padova, Padova, Italia at the Prof. Maurizio Casarin group.
*
Author to whom correspondence should be addressed.
Academic Editor: James W. Gauld
Received: 8 October 2018 / Accepted: 8 November 2018 / Published: 10 November 2018
(This article belongs to the Special Issue Theoretical Investigations of Reaction Mechanisms)
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Abstract

The mechanism of the addition of indazole (Ind)—a bifunctional aromatic N,NH-nucleophile—to cyclohexyl isocyanide coordinated to the palladium(II) center in the model complex cis-[PdCl2(CNMe)(CNCy)] (1) to give the corresponding aminocarbene ligand was investigated in detail by theoretical (DFT) methods. The most plausible mechanism of this reaction is that of the associative type involving nucleophilic attack of Ind by its unprotonated N atom at the isocyanide carbon atom followed by the stepwise proton transfer from the nucleophile molecule to the isocyanide N atom via deprotonation/protonation steps. Two reaction channels based on two tautomeric forms of indazole were found. The channel leading to the experimentally isolated aminocarbene product is based on the less stable tautomeric form. Another channel based on the more stable tautomer of Ind is slightly kinetically more favorable but it is endergonic. Thus, the regioselectivity of this reaction is thermodynamically rather than kinetically driven. The bonding situation in key species was analyzed. View Full-Text
Keywords: isocyanides; nitriles; nucleophilic addition; DFT calculations; activation of small molecules; reaction mechanism isocyanides; nitriles; nucleophilic addition; DFT calculations; activation of small molecules; reaction mechanism
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Casella, G.; Casarin, M.; Kukushkin, V.Y.; Kuznetsov, M.L. Reaction between Indazole and Pd-Bound Isocyanides—A Theoretical Mechanistic Study. Molecules 2018, 23, 2942.

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