Coordinates, atomic fragment centered

The phosphorus atom of the cyclophosphazene ring can also be involved in interaction with transition metal atoms either by a coordinate or by a covalent linkage. The former occurs with hydridocyclo-phosphazenes by a tautomerization of the P-H to result in a P(III) center (222). The covalent mode of linkage occurs by the reaction of the appropriate organometallic or metal fragment with the halo-genocyclophosphazenes (223). 

In the transformation of a 1-alkyne to a vinylidene in the coordination sphere of a transition metal, the migrating hydrogen atom plays a key role. Usually, ancillary ligands on the metal are only spectators and do contribute to small modifications of the bonding properties of the metal fragment. However, if a hydride is present as a ligand to the transition metal center, it may interfere with the alkyne to vinylidene transformation. This may open up new selective and efficient routes to vinylidene complexes. 

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