Phosphinidenes

Of the low-valent organophosphorus compounds phosphinidenes occupy a special place. In 'free' phosphinidenes the phosphorus atom carries a single substituent. Such species prefer a triplet electronic ground state. Little is known about these species experimentally in contrast to those that carry a transition metal group. Depending on the ancillary ligands these carbene-like reagents can have electrophilic or nucleophilic properties. The comparison with Fischer-type and Schrock-type carbene complexes is tempting. In this survey, an analysis is given on the electronic characteristics of the phosphinidenes with and without transition metal groups. Synthetic approaches to the terminal complexed phosphinidenes are summarized and their reactivities are evaluated.