Dinickel-Catalyzed Vinylidene–Alkene Cyclization Reactions

Abstract

A dinickel catalyst promotes reductive cyclization reactions of 1,1-dichloroalkenes containing pendant olefins. The reactions can be conducted with a Zn reductant or electrocatalytically using a carbon working electrode. Mechanistic studies are consistent with the intermediacy of a Ni2(vinylidene) species, which adds to the alkene and generates a metallacyclic intermediate. β-Hydride elimination followed by C–H reductive elimination forms the cyclization product. The proposed dinickel metallacycle is structurally characterized and its stoichiometric conversion into product is demonstrated. Spin-polarized, unrestricted DFT calculations are used to further examine the cyclization mechanism. These calculations reveal that both nickel centers function cooperatively to mediate the key oxidative addition, migratory insertion, β-hydride elimination, and reductive elimination steps.

A dinickel-catalyzed three-component cycloaddition of vinylidenes

“…The calculated structure of 47a is analogous to the metallacycle that we experimentally characterized from the intramolecular addition of a vinylidene to an alkene. 13 …”

“…The calculated structure of 47a is analogous to the metallacycle that we experimentally characterized from the intramolecular addition of a vinylidene to an alkene. 13 Binding of the second aldehyde to form 48 is exothermic by 3.8 kcal mol À1 , and the second migratory insertion to form 50 has a low activation barrier of 3.1 kcal mol À1 . Ogoshi described a mechanistically related head-to-tail coupling of aldehydes in a Tischenko-type reaction.…”

“…We were recently successful in arresting this process and obtaining direct experimental characterization of metallacycle 1. 13 Based on this stepwise mechanism, we wondered whether metallacycles such as 1 could be intercepted with a third reaction partner to form rings larger than cyclopropanes. Here, we provide an example of such a transformation in the context of a [2 + 2 + 1]-cycloaddition of two aldehyde equivalents and a vinylidene.…”

“…We were recently successful in arresting this process and obtaining direct experimental characterization of metallacycle 1. 13 …”

Dinuclear Influence on the Mechanism, Reactivity, and Selectivity During Rh-Al Catalyzed Aryl Ether C-O Bond Reduction/Defunctionalization

“…Therefore, our group is using density functional theory (DFT) calculations to understand the origin and influence of dinuclear effects on catalytic reactions, especially bond activation reactions. 16,17,18,19,20,21,22,23 For heterodinuclear complexes with two transition metals or a transition metal and a maingroup metal, there are now several classic examples of bond activation reactions. For example, Bergman showed that an Ir−Zr complexes with Cp ligands can stoichiometrically activate/break C−O, O−H, and N−H bonds through addition to both metal centers.…”