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Insertion, Rearrangement, and Coupling Processes in the Reactions of the Unsaturated Hydride Complex [W25‑C5H5)2(H)(μ-PCy2)(CO)2] with Isocyanides

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posted on 26.08.2013, 00:00 by M. Angeles Alvarez, M. Esther García, Daniel García-Vivó, Miguel A. Ruiz, M. Fernanda Vega
The title complex reacted with stoichiometric amounts of CNR rapidly at room temperature or below to give two types of formimidoyl derivatives: the symmetrically bridged complexes [W2Cp2(μ-C,N:C,N-HCNR)­(μ-PCy2)­(CO)2] (R = tBu (W–W = 2.8645(5) Å), 4-C6H4OMe), and the asymmetrically bridged [W2Cp2{μ-C:N-HCN­(Xyl)}­(μ-PCy2)­(CO)2] (Cp = η5-C5H5; Xyl = 2,6-C6H3Me2). The latter complex underwent slow isomerization at room temperature to give the corresponding aminocarbyne derivative [W2Cp2{μ-CNH­(Xyl)}­(μ-PCy2)­(CO)2], which in turn could be decarbonylated through irradiation with UV–vis light to yield the 30-electron aminocarbyne complex [W2Cp2{μ-CNH­(Xyl)}­(μ-PCy2)­(μ-CO)] (W–W = 2.4928(4) Å). Density functional theory calculations revealed that the aminocarbyne complex was the most stable isomer for the three isocyanides under study, while subtle steric effects marked the relative stability of the formimidoyl isomers, which therefore are the kinetic products of these reactions. The reaction of the title complex with excess CN­(4-C6H4OMe) at room temperature gave in good yield the complex [W2Cp2(μ-C,N:C,C′-HCN­(4-C6H4OMe)­C­{N­(4-C6H4OMe)})­(μ-PCy2)­(CO)2] (W–W = 2.9370(2) Å), having a 5-electron donor aminocarbene-iminoacyl ligand derived from the N–C coupling of formimidoyl and isocyanide ligands, whereas the analogous reaction with CNXyl gave the aminocarbyne complex [W2Cp2{μ-CNH­(Xyl)}­(μ-PCy2)­{CN­(Xyl)}­(CO)] (W–W = 2.677(2) Å) having a terminal bent isocyanide ligand.