Complex zirconium phosphinidene

The bridging zirconium phosphinidene complexes in Fig. 7.30 are expected to resonate upheld from the terminal ones in Fig. 7.29, since terminal phosphinidene complexes are far better suited for. -donor interactions of the phosphorus atom towards the metal than are the bridging ligands. 

The electronic structures of the two complexes depicted in Fig. 7.31 present us with somewhat of a challenge in explaining their respective phosphorus resonances. The chloro-complex on the left clearly has a different electronic contribution from the phosphinidene hgand toward zirconium than the phosphane adduct on the right. A simple electron count on the respechve zirconium atoms suggests that in the chloro-complex, the phosphinidene may act as a three electron donor, whereas in... 

The difference in the phosphorus resonance for a terminal and a bridging phosphinidene complex can be seen in a series of zirconium complexes shown in Figs. 7.29 and 7.30. 

As a first step towards understanding this phenomenon, it helps to realize that the structure of the chloro-complex in Fig. 7.31 comes from a x-ray crystal structure determination, and is thus the structure of the complex in the solid state and not in solution. It also helps to note that the zirconium moiety is an anion (LF is the counter cation), making the phosphinidene-ligand effectively a two electron donor. 

Interest has again continued in studies of the generation and reactivity of phosphinidene species (RP ), phosphorus analogues of carbenes, and this area has been reviewed. A review has also appeared of the use of terminal phosphinidene complexes in the formation of phosphorus-element bonds. Further studies of phosphanylidene-a -phosphoranes, RP = PR3, (regarded as phosphine-complexed phosphinidenes, i.e., ArP -PRs), have shown that the species Me3P=PAr (Ar = Mes or 2,6-Mes2C6H3) are good vehicles for the delivery of the terminal phosphinidene moiety ArP to zirconium and vanadium sites. Terminal phosphinidene complexes of cobalt, ruthenium, rhodium and osmium, and iridium, have also been... 

---