Iridium pyrazolate complexes reaction with

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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