Co-Complexes Derived from Alkene Insertion to Alkyne-Dicobaltpentacarbonyl Complexes: Insight into the Regioselectivity of Pauson−Khand Reactions of Cyclopropenes

Abstract

Described are the X-ray crystallographic and spectral properties of Co-complexes that were isolated from two Pauson-Khand reactions of chiral cyclopropenes. These are the first examples of isolated Co-complexes derived from the putative alkene-insertion intermediates of Pauson-Khand reactions. The binuclear Co-complexes are coordinated to μ-bonded, five-carbon "flyover" carbene ligands. It is proposed that the complexes result from cyclopropane fragmentation subsequent to alkene insertion. The observation of these metal complexes provides a rationale for the origin of regioselectivity in Pauson-Khand reactions of cyclopropenes.

Regioselectivity of the Pauson–Khand reaction in single-walled carbon nanotubes

“…As a matter of fact, CO-bridging ligand complexes have been previously reported. 85 Moreover, the distances of 1.83 and 2.96 Å in CP1′ between C-Co suggest that only one Co atom is η 2 -coordinated to the alkyne, and the other is η 1 -coordinated. A similar observation is done for CP2′.…”

A Decade of Advancements in Pauson–Khand‐Type Reactions

“…In 2008, Fox and coworkers reported the first examples of isolated Co complexes derived from the putative alkene‐insertion intermediates of Pauson–Khand reactions (Scheme ) 11. The binuclear Co complexes were coordinated to five‐carbon, μ‐bonded “flyover” carbene ligands.…”

Phosphine–Alkene Ligands as Mechanistic Probes in the Pauson–Khand Reaction

“…[10] During failed attempts at inserting cyclopropene into Co 2 -alkyne complexes, Fox et al identified various sideproducts. [11] More recently, Evans and McGlinchey isolated and characterized (by X-ray diffraction) compounds 1 a-e, type III complexes in which an olefin is intramolecularly coordinated to a cobalt atom (Scheme 2). [12] Interestingly, complexes 1 do not undergo alkene insertion to give the corresponding PK adducts; the authors have attributed this lack of reactivity to two factors: the severe strain in the final PK adduct and the pseudoequatorial position of the alkene in complexes 1.…”

“…During failed attempts at inserting cyclopropene into Co 2 –alkyne complexes, Fox et al. identified various side‐products 11. More recently, Evans and McGlinchey isolated and characterized (by X‐ray diffraction) compounds 1 a – e , type III complexes in which an olefin is intramolecularly coordinated to a cobalt atom (Scheme ) 12.…”