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

• Autor(a) principal: Alegria, Elisabete
• Data de Publicação: 2016
• Outros Autores: Guedes Da Silva, M. Fátima C., Kuznetsov, Maxim L., Martins, Luisa, Pombeiro, Armando
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.21/7148
• topic: Cyanoimido complexes; Alkylated cyanoimido; Digital simulation of cyclic voltammetry; Electron-transfer induced reactions; Double square ECEC-type mechanism

Treatment of trans-[Mo(NCN)(2)(dppe)(2)] with alkyl halides (RX) affords the alkylated cyanoimidocomplexes trans-[Mo(NCN)(NCNR)(dppe)(2)]X [R = Me, X = I (1); R = Et, X = I (2); R = Pr, X = I (3); R = Pr-i, 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.