Tripodal polyphosphine

Another example of selective C=C bond hydrogenation has arisen from mechanistic studies on an iron m-hydride dihydrogen complex, [Fe(PP3)(FI)(H2)](BF4) [PP3 = P(CH2CH2PPh2)3], a catalyst inactive with alkene substrates. Scheme 6 shows that no decoordination of dihydrogen is required in any step of the cycle and that the vacant site is created by unfastening of one of the P-donor atoms (species (16)).50 Extensive studies on catalytic alkene hydrogenation by analogous tripodal (polyphosphine) Rh, Os, and Ir complexes have been carried by Bianchini and co-workers.51,52... 

Bianchini, C., Burnaby, D. G., Evans, J., Frediani, P., Meli, A., Oberhauser, W., Psaro, R., Sordelli, L. and Vizza, F. Preparation, characterization, and performance of tripodal polyphosphine rhodium catalysts immobilized on silica via hydrogen bonding, J. Am. Chem. Soc., 1999, 121, 5961-5971. 

Figure 4 Reversible reaction of H2 or C2H4 with tripodal polyphosphine cobalt complex 4.

Scheme 10 depicts the structure assigned to Co2Rh2(CO)6(p-CO)3 HC(PPh2)3 [128]. The tripodal polyphosphine HC(PPh2)3 binds to the basal Rh2Co face of the metallic tetrahedron. 

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