Tris(pyrrolyl)phosphine-Substituted Acetylene−Dicobaltcarbonyl Complexes:  Syntheses, Structural Characterization, and Reactivity Studies

The first tris(pyrrolyl)phosphine-substituted alkyne−dicobaltcarbonyl complexes have been prepared by reaction of the corresponding dicobalthexacarbonyl complexes with tris(pyrrolyl)phosphine, and their solid-state structures have been studied by X-ray diffraction. In accordance with the strong π-acceptor character of the tris(pyrrolyl)phosphine ligand, these complexes present a Pauson−Khand reactivity very similar to that of the parent, unsubstituted ones. On the other hand, the cobalt-stabilized propargyl cations derived from tris(pyrrolyl)phosphine-substituted (2-propynol)dicobaltcarbonyl complexes undergo an unprecedented intramolecular Nicholas reaction in which one of the pyrrole rings acts as an internal nucleophile, and that gives rise to a new structural type of chelated alkyne−dicobaltcarbonyl complexes.