Abstract
Homoleptic eightfold coordinated methyl isocyanide complexes of W(IV) and W(V) have been prepared for the first time. The reaction of [NBu4]4[W(CN)8] with methyl triflate (MeOTf) gives [W(CNMe)8][OTf]4. The even stronger methylating mixture of methyl fluoride (MeF) and arsenic pentafluoride (AsF5) in liquid sulfur dioxide (SO2) is able to fully alkylate both [NBu4]4[W(CN)8] and [NBu4]3[W(CN)8]. The paramagnetic octakis(methyl isocyanide)tungsten(V) complex [W(CNMe)8][AsF6]5 is thermally highly unstable above -30 °C. All compounds have been characterized via single-crystal X-ray diffraction and IR, Raman, and NMR or EPR spectroscopy.
Highlights
To carbonyl ligands, isocyanides (C≡N-R) are good ligands for metals in low oxidation states
Due to the long reaction times and the formation of side-products, we looked for an alternative procedure for alkylation
The reaction time can be reduced to under one hour at −78 °C by using the powerful methylating agent [MeOSO][AsF6]22 and the formation of side products is less pronounced. As octacyanotungstate exists both in the tetra- and pentavalent state, we wondered if [W(CN)8]3− could be fully methylated. [NBu4]3[W(CN)8] is accessible via the oxidation of potassium octacyanotungstate(IV) in water with nitric acid,[27] followed by precipitation with tetrabutylammonium cations in water
Summary
To carbonyl ligands, isocyanides (C≡N-R) are good ligands for metals in low oxidation states. Single crystals of [W(CNMe)8][OTf]4 suitable for X-ray diffraction could be obtained after one day by vapor diffusion of diethyl ether into an acetonitrile solution of the product at room temperature (CCDC 2058758).
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