Phosphorus atoms of organophosphorus compounds have empty d orbitals and many valence states, mainly in the following categories:
①Three-coordinate phosphorus compounds. For the sp3 (inequality) hybrid triangular pyramid configuration, the phosphorus atom with a lone pair of electrons. Trivalent phosphorus compounds have electrophilic, amphiphilic and diene-philic reaction characteristics, and often form strong PO bonds during the reaction. For example, trialkylphosphines and trialkyl phosphites are both trivalent phosphorus compounds. The nucleophilicity and basicity of trialkylphosphine are greater than that of trialkylamine due to the larger volume and lower electronegativity of phosphorus atom. Phosphines with 3 different alkyl groups can be resolved into optical isomers. Trialkylphosphines are also easily coordinated with transition metals to form characteristic homogeneous catalysts.
② Four-coordinate phosphorus compounds. It is a sp3-hybridized tetrahedral configuration, including a quaternary phosphonium ion R4P+ and a pentavalent phosphoryl compound X3PO. The PO bond stability of these compounds is very high. Optical isomers of tetracoordinate phosphorus compounds are easier to resolve.
③ Penta-coordinate phosphorus compounds. It is a trigonal bipyramid (hexahedral) configuration of sp3d hybridization, such as phosphine: pentacoordinate phosphorus organic compounds have a series of molecular reorganization properties, and many tetracoordinate phosphorus organic compounds form pentacoordinate intermediates in the reaction .
④ Six-coordinate phosphorus compounds. Quadrangular bipyramidal (octahedral) configurations hybridized for sp3d2, such as hexacoordinated phosphorus anions and cyclic phosphates: These compounds are very reactive and not much studied.
In addition, the research on mono- and di-coordinate phosphorus compounds is currently very extensive.