N-Heterocyclic Carbene Adducts of Molybdenum Tetracarboxylate Complexes

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• 作者：Thomas P. Robinson ; Andrew L. Johnson ; Paul R. Raithby ; Gabriele Kociok-Kohn
• 刊名：Organometallics
• 出版年：2016
• 出版时间：August 8, 2016
• 年：2016
• 卷：35
• 期：15
• 页码：2494-2506
• 全文大小：708K
• 年卷期：0
• ISSN：1520-6041

文摘

Treatment of the quadruply bonded dimolybdenum complexes [Mo₂(μ-O₂CCF₃)₄] (1), [Mo₂(μ-O₂CCH₃)₄] (2), and [Mo₂(μ-O₂CBu^t)₄] (3) with the N-heterocyclic carbenes (NHCs) L (L^a = IPr, L^b = IMes, L^c = IⁱPr₂Me₂, and L^d = IEt₂Me₂) results in the formation of a series of 1:1 and 1:2 adducts. In the case of the larger, and more sterically demanding, carbene ligands, i.e. L^a and L^b, coordination exclusively occurs axially with respect to the [Mo₂] complexes and occurs only once in the case of L^a, [Mo₂(μ-O₂CR)₄(L^a)] (R = Me, ^tBu, CF₃) (1a–3a), and twice in the case of L^b, [Mo₂(μ-O₂CCF₃)₄(L^b)₂] (2b). For the less sterically demanding carbene ligands (L^c and L^d) coordination to the [Mo₂] core occurs twice, with a transoidal distribution about the [Mo₂] unit and is exclusively in equatorial positions, resulting in partial displacement of two of the bridging {μ-O₂CR} ligands in each complex. In the case of complexes 1a–3a, 2b, [Mo₂(μ-OTFA)₂(OTFA)₂(L^c)₂] (1c), [Mo₂(μ-OTFA)₂(OTFA)₂(L^d)₂] (1d), and [Mo₂(μ-OAc)₂(OAc)₂(L^d)₂] (2d) the solid-state molecular structures have been unambiguously characterized by single-crystal X-ray diffraction. As part of our study into the reactivity of NHC ligands with [Mo₂(μ-O₂CCH₃)₄], the heteroleptic NHC adduct [Mo₂(μ-OAc)₂Cl₂(L^d)₂] (5) formed from the reaction of complex 2d with trimethylsilyl chloride has also been isolated and structurally characterized using single-crystal X-ray diffraction. As part of our study the Mo–Mo stretching frequencies of these complexes have been analyzed by Raman spectroscopy.