Tris(pyrrolyl) phosphine-substituted acetylene-dicobaltcarbonyl complexes:Syntheses, structural characterization, and reactivity studies

The first tris(pyrrolyl)phosphine-substituted alkyne-dicobaltcarbonyl compl exes have been prepared by reaction of the corresponding dicobalthexacarbon yl complexes with tris(pyrrolyl)phosphine, and their solid-state structures have been studied by X-ray diffraction. In accordance with the strong pi-a cceptor character of the tris(pyrrolyl)phosphine ligand, these complexes pr esent a Pauson-Khand reactivity very similar to that of the parent, unsubst ituted ones. On the other hand, the cobalt-stabilized propargyl cations der ived from tris(pyrrolyl)phosphine-substituted (2-propynol)dicobaltcarbonyl complexes undergo an unprecedented intramolecular Nicholas reaction in whic h one of the pyrrole rings acts as an internal nucleophile, and that gives rise to a new structural type of chelated alkyne-dicobaltcarbonyl complexes .