Boron trifluoride etherate, strictly boron trifluoride diethyl etherate, or boron trifluorideâÂÂether complex, is the chemical compound with the formula BF<sub>3</sub>O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>, often abbreviated BF<sub>3</sub>OEt<sub>2</sub>. It is a colorless liquid, although older samples can appear brown. The compound is used as a source of boron trifluoride in many chemical reactions that require a Lewis acid. The compound features tetrahedral boron coordinated to a diethylether ligand. Many analogues are known, including the methanol complex.
Boron trifluoride etherate serves as a source of boron trifluoride according to the equilibrium:
The BF<sub>3</sub> binds to even weak Lewis bases, inducing reactions of the resulting adducts with nucleophiles.