The Development of a Carbene‐like Chemistry with Terminal Phosphinidene Complexes

When compared to the chemistry of other well‐known electron‐deficient species such as carbenes, silylenes, and nitrenes, the chemistry of phosphinidenes RP: is extremely underdeveloped. A critical survey of the literature indicates that this state of affairs probably reflects both an inadequate access to these species and an intrinsic lack of reactivity. Theoretical calculations suggest that it is possible to boost the electrophilicity and to stabilize the singlest state of phosphinidenes by complexation with transition‐metal moieties such as M(CO) 5 (MCr, Mo, W). The corresponding terminal phosphinidene complexes [RPM(CO) 5 ] show a rich and varied chemistry which often parallels the chemistry of singlet carbenes. Phosphinidene complexes are presently easily accessible through thermal decomposition of 7‐phosphanorbornadiene complexes, but their stabilization remains a challenge to be met.