Mónica H. Pérez-Temprano

Bimetallic Catalysis using Transition and Group 11 Metals: An Emerging Tool for CC Coupling and Other Reactions

Bimetallic catalysis refers to homogeneous processes in which either two transition metals (TM), or one TM and one Group 11 (G11) element (occasionally Hg also), cooperate in a synthetic process (often a C-C coupling) and their actions are connected by a transmetalation step. This is an emerging research area that differs from the isolated or tandem applications of the now classic processes (Stille, Negishi, Suzuki, Hiyama, Heck). Most of the reactions used so far combine Pd with a second metal, often Cu or Au, but syntheses involving very different TM couples (e.g., Cr/Ni in the catalyzed vinylation of aldehydes) have also been developed. Further development of the topic will soon demand a good knowledge of the mechanisms involved in bimetallic catalysis, but this knowledge is very limited for catalytic processes. However, there is much information available, dispersed in the literature, coming from basic research on exchange reactions occurring out of any catalytic cycle, in polynuclear complexes. These are essentially the same processes expected to operate in the heart of the catalytic process. This Review gathers together these two usually isolated topics in order to stimulate synergy between the bimetallic research coming from more basic organometallic studies and the more synthetic organic approaches to this chemistry.

Strong Metallophilic Interactions in the Palladium Arylation by Gold Aryls

Its the second step that counts: arylation of Pd by Au takes place through transition states and intermediates featuring strong Au⋅⋅⋅Pd metallophilic interactions. However, the aryl transfer from [AuArL] to [PdArClL(2)] is thermodynamically disfavored and will not occur unless an irreversible Ar-Ar coupling from [PdAr(2)L(2)] follows.

Observation of a hidden intermediate in the Stille reaction. Study of the reversal of the transmetalation step.

A study of the reaction of cis-[PdRf2(AsPh3)2] (Rf = 3,5-C6Cl2F3) with ISnBu3 (that is the reversal of the natural Stille reaction of [PdRfI(AsPh3)2] with RfSnBu3) allows for the observation of cis-[PdRf2(AsPh3)(ISnBu3)], the expected intermediate from a cyclic transmetalation in the direct Stille reaction, thus providing experimental support to the operation of cyclic transmetalation pathways.

Capturing Elusive Cobaltacycle Intermediates: A Real‐Time Snapshot of the Cp*CoIII‐Catalyzed Oxidative Alkyne Annulation

Despite Cp*CoIII catalysts having emerged as a very attractive alternative to noble transition metals for the construction of heterocyclic scaffolds through C-H activation, the structure of the reactive species remains uncertain. Herein, we report the identification and unambiguous characterization of two long-sought cyclometalated Cp*CoIII complexes that have been proposed as key intermediates in C-H functionalization reactions. The addition of MeCN as a stabilizing ligand plays a crucial role, allowing the access to otherwise highly reactive species. Mechanistic investigations demonstrate the intermediacy of these species in oxidative annulations with alkynes, including the direct observation, under catalytic conditions, of a previously elusive post-migratory insertion seven-membered cobaltacycle.