Phosphine oxide

An ${\mathrm{R}}_3\mathrm{PO}$ compound with approximately tetrahedral phosphorus. Its short, strongly polar P–O bond can be described using ionic contributions and oxygen lone-pair donation into P–R antibonding orbitals, without requiring large phosphorus 3d participation.

The phosphine oxide $\mathrm{M}{\mathrm{e}}_3\mathrm{PO}$, with three P–C bonds and one terminal P–O bond.