Iridium pyrazolate complexes, reaction

It is well known that hydride derivatives of transition metals can be prepared by hydrogen-transfer reactions from primary and secondary alcohols. Penta-methylcyclopentadienyl (/i-pyrazolate)-( t-hydrido) complexes of iridium and rhodium were obtained by using propan-2-ol as the hydride source (128, 150). 

The efficiency of the rhodium catalyst was compared with that of the iridium complex [lr(PyP)(CO)2]BPli4 (PyP = l-[2-(diphenylphosphino)ethyl]pyrazole). The latter resulted more effective for the cyclization of aliphatic substrates, whereas the Rh-complex was significantly more efficient in the reaction of aromatic substrates. The mechanism was studied by low-temperature NMR spectroscopy and deuteration experiments. Unlike what is reported in their previous work [31], the authors postulate an alternative catalytic cycle in which the initial step of the reaction cycle involves the association of the alkyne with the metal center, but unfortunately the mechanistic studies were done only on the Ir-complex. 

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