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 pi-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.