Copper(II) tetrafluoroborate or cupric tetrafluoroborate is any inorganic compound with the formula Cu(H2O)x(BF4)2. As usually encountered, it is assumed to be the hexahydrate (x = 6),Vakulka, A., Goreshnik, E. Copper(II) Tetrafluoroborate Hexahydrate: Preparation, Structure and Raman Spectrum. J Chem Crystallogr 54, 157–162 (2024). https://doi.org/10.1007/s10870-024-01008-3 but this salt can be partially dehydrated to the tetrahydrate. Regardless, these compounds are aquo complexes of copper in its +2 oxidation state, with two weakly coordinating tetrafluoroborate anions.
Applications The compound is used in organic synthesis, e.g. as a Lewis acid for Diels Alder reactions, for cyclopropanation of alkenes with diazo reagents, and as a Lewis acid in Meinwald rearrangement reactions on epoxides. In the former two applications, the copper(II) is reduced to a copper(I) catalyst.Ilhyong Ryu, Noboru Sonoda, "Copper(II) Tetrafluoroborate" Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley & Sons.
The compound is also used for copper electroplating in fluoroborate-based plating baths.
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