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Metal–Metal Quadruple Bonds (M = Mo or W) Supported by 4‑[2-(4-Pyridinyl)ethenyl] Benzoates and their Complexes with Tris(pentafluorophenyl)boron

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posted on 2015-12-07, 00:00 authored by Malcolm H. Chisholm, Christopher J. Ziehm
From the reactions between M2(TiPB)4 and two equivalents of the acids LH, the compounds trans-M2(TiPB)2L2 were isolated where M = Mo, compound I, and M = W, II, TiPB = 2,4,6-triisopropylbenzoate, and LH = 4-[2-(4-Pyridinyl)­ethenyl]­benzoic acid. In related reactions when tris­(pentafluorophenyl)­boron, A, was added, the Lewis acid–Lewis base complexes Mo2(TiPB)2(LA)2, IB, and W2(TiPB)2(LA)2, IIB, were isolated. Compounds I and IB are red and purple, respectively, while II and IIB are green. The new compounds have been characterized by 1H NMR, UV–visible-NIR absorption spectroscopy, and electrochemical studies, which are tied together with density functional theory, DFT, and time-dependent DFT calculations. Chemical reduction of IB and IIB yields anions where the single electron occupies a ligand-based orbital as indicated by EPR spectroscopy. The LUMO and LUMO+1 are ligand-based, and are close in energy, and upon reduction, no IVCT is observed.

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