Boron trifluoride etherate

Boron trifluoride etherate, strictly boron trifluoride diethyl etherate, or boron trifluoride–ether complex, is the chemical compound with the formula BF3O(C2H5)2, often abbreviated BF3OEt2. 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.

Reactions
Boron trifluoride etherate serves as a source of boron trifluoride according to the equilibrium:
 * BF3OEt2 BF3 + OEt2

The BF3 binds to even weak Lewis bases, inducing reactions of the resulting adducts with nucleophiles.