The mononuclear hydride
PH5, systematically named λ5-phosphane, and its hydrocarbyl derivatives. By extension, the literature also applies the term to phosphonium ylides.
See also: phosphanes
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1358 (https://doi.org/10.1351/pac199567081307)