Mono-alkylation of cyanoimide at a molybdenum(IV) diphosphinic center by alkyl halides: synthesis, cathodically induced isomerization and theoretical studies

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• 作者：Elisabete C.B.A. Alegria^a ; ^b ; ^{ebastos@deq.isel.ipl.pt" class="auth_mail" title="E-mail the corresponding author} ; M. Fá ; tima C. Guedes da Silva^a ; ^{fatima.guedes@tecnico.ulisboa.pt" class="auth_mail" title="E-mail the corresponding author} ; Maxim L. Kuznetsov^a ; Luí ; sa M.D.R.S. Martins^a ; ^b ; Armando J.L. Pombeiro^a ; ^{pombeiro@tecnico.ulisboa.pt" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Cyanoimido complexes ; alkylated cyanoimido ; digital simulation of cyclic voltammetry ; electron-transfer induced reactions ; double square ECEC-type mechanism
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：10 November 2016
• 年：2016
• 卷：218
• 期：Complete
• 页码：252-262
• 全文大小：1335 K

文摘

Treatment of trans-[Mo(NCN)₂(dppe)₂] with alkyl halides (RX) affords the alkylated cyanoimido-complexes trans-[Mo(NCN)(NCNR)(dppe)₂]X [R = Me, X = I (1); R = Et, X = I (2); R = Pr, X = I (3); R = ⁱPr, X = I (4); R = CH₂Ph, X = Br (5); R = CH₂C₆H₄NO₂-4, X = Br (6)], while its reaction with the trimethyloxonium salt [Me₃O][BF₄] affords trans-[Mo(NCN)(NCNMe)(dppe)₂][BF₄] (7). The reactions are accelerated by microwave irradiation. Complexes 1-7 were fully characterized by elemental analyses, IR and NMR spectroscopies, FAB-MS spectrometry, cyclic voltammetry and controlled potential electrolysis. The electrophilic addition to the exo-N atom of one of the cyanoimide ligands was confirmed by single crystal X-ray crystal analysis of 1. In aprotic medium and at a Pt electrode, compounds 1-7 undergo, apart from two consecutive single-electron reversible oxidations, also two successive single-electron reductions at different potentials, involving a cathodically induced trans-to-cis isomerization, following a double square ECEC-type mechanism which was studied in detail by digital simulation of the cyclic voltammograms. Quantum-chemical calculations indicate that the oxidations and reductions are mainly metal centered (although the latter with some involvement of the cyanoimide moieties), and that the reduction leads to a decrease of the relative stability of the trans isomer vs. the cis one.