Phosphinate

Phosphinate is a class of organophosphorus compounds containing the phosphinate functional group. In neutral form, the core motif is R2P(O)OR', featuring a phosphoryl P=O bond attached to two carbon substituents (R) and one oxygen substituent (OR'). The phosphorus is in the +5 oxidation state. The corresponding phosphinate anion, [R2P(O)O]−, forms salts with various counterions; salts of metals or other cations are common. Phosphinates thus appear as esters of phosphinic acids (phosphinate esters) and as salts (phosphinate salts).

Classification and nomenclature: Phosphinate esters have the formula R2P(O)OR', while deprotonated forms are phosphinate salts. The term can also refer to the anion of phosphinic acid, depending on context.

Synthesis: Phosphinate esters are typically prepared by oxidation of dialkyl phosphites or by substitution on chlorophosphoranes with alcohols. Deprotonation of the phosphinic acid form yields phosphinate salts, which can be isolated as metal or organic cation salts.

Properties: The P=O bond confers polarity and high oxygen-donor ability. Phosphinates are generally stable under ambient conditions but can hydrolyze under certain acidic or basic environments, depending on substituents. They behave as ligands in coordination chemistry and as reactive precursors in organic synthesis.

Applications: Phosphinates are used as ligands in homogeneous catalysis, where they can function as either bidentate or monodentate donors to transition metals. They also serve as intermediates in the synthesis of pharmaceuticals, agrochemicals, and polymers; some phosphinate esters are explored as flame retardants or plasticizers in polymer formulations.