In organic chemistry, phosphonites are organophosphorus compounds with the formula P(OR)<sub>2</sub>R. They are found in some pesticides and are used as ligands.
Although they are derivatives of phosphonous acid (RP(OH)<sub>2</sub>), they are not prepared from such precursors. Phosphonites are prepared by alcoholysis of organophosphinous chlorides. For example, treatment of dichlorophenylphosphine with methanol and base gives dimethyl phenylphosphonite:
Oxidation of phosphonites gives phosphonates:
Phosphonites can function as ligands in homogeneous catalysis.