Rare-Earth Metal Phosphinidene Complexes: A Trip from Bridging One to Terminal One.

ConspectusAs phosphorus analogues of alkylidene (or carbene) and imido (or nitrene) complexes, phosphinidene complexes have received great attention not only for their fundamental scientific merits but also for their ability to build new phosphorus-containing molecules. A large number of phosphinidene complexes in bridging, mononuclear, or terminal coordination modes have been synthesized, and their reactivity has been extensively explored. However, the synthesis of rare-earth metal (scandium, yttrium, and lanthanide metal) phosphinidene complexes lagged behind the transition metal and actinide congeners for decades. Rare-earth metal ions are among the hardest Lewis acids, whereas phosphinidene ligands are soft Lewis bases; rare-earth metal-phosphinidene coordination is thus mismatched based on the Pearson's HSAB principle. The bridging rare-earth metal phosphinidene complexes were not reported until 2008, and the synthesis of the mononuclear and terminal species is even more challenging, which has only recently been achieved.Our group reported a bis(