Phosphaalkynes, coordination modes

Phosphaalkynes have a rich coordination chemistry, in which both the triple bond and the lone pair of the P atom can participate. Table 15.5.3 lists the coordination modes of phosphaalkynes, and two structures are shown in Fig. 15.5.5. 

Phosphaalkynes RC=P display a rich coordination chemistry, and five different modes of ligation (M-Q) may be discerned in phosphaalkyne transition-metal complexes (Scheme 25).3,51 According to theoretical calculations and to photoelectron spectroscopic investigations, the doubly degenerated jr-orbitals of the triple bond are the HOMOs in phosphaalkynes. In keeping with this, the rj2-coordination modes N-Q are usually realized with transition metals. Complexes with rjMigated phosphaalkynes M are only possible when the respective ensemble of metal atom and ancillary ligands form an appropriate pocket, which only allows rj1-coordination by a linear molecule.3,sl... 

Reaction of the phosphaalkyne complex Pt(dppe)(f/2-P=CtBu) with either Fe2(CO)9 or Fe3(CO)12 affords high yields of the red cluster Fe2Pt-(A<3-( /2--L)-P=OBu)(CO)6(dppe) (55), which contains a novel /i3-(f/2-1) phosphaalkyne ligand (140,140a). This bonding mode is similar to the alkyne coordination observed in some alkyne clusters, such as Fe3(/i3-(f/2- )-PhC=CPh)(CO)9 (141), and the low value of J(195Pt-31P) = 128 Hz indicates that the P atom of the phosphaalkyne is not coordinated to the Pt... 

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