The mononuclear
hydridePH5
,
systematically named

-phosphane, and its hydrocarbyl derivatives. By extension, the literature also applies
the term to
phosphonium ylides.
Source:
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1358