Copper-bifluoride complex

More recently, a copper-bifluoride complex has been described, starting once again from the alkoxide species. Subsequently, [Cu(NHC)2] [HF2] complexes were developed (Figure 8.2) [91]. Both complexes were highly air stable in the solid state and moderately stable in solution compared to their analog [Cu(F) (IPr)] [92]. Remarkably, catalytic activity was observed in several transformations such as the reduction of ketones, the 1,4-conjugated borylation and silylation, and the diastereoselective allylation. 

Ammonium bifluoride, when used at 0.5%, is also useful in assisting the removal of magnetite-based deposits. Add 2 to 3% thiourea where copper is present. The use of excess thiourea [CS(NH2>2] complexes dissolved copper and prevents it from plating out on steel surfaces and causing an equivalent amount of iron to dissolve. The heat exchanger must be thoroughly flushed out to remove all traces of copper and also inspected. 

Determination of copper in an unknown. Add 10 mL of 6 M HNO3 to each of three clean 250-inL Erlenmeyer flasks and take these to your instructor, who will add an unknown sample to each. (This unknown may be copper foil as used m the standardization.) Dissolve each and titrate as described for the standardization of Na2S203. Note In place of H3PO4, approximately 2 g ammonium bifluoride, NH4HF2 or NH4F HF, may be added to complex any iron and at the same time adjust the solution to the proper acidity. This experiment is also suitable for determining copper in about 0.3 g brass. 

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