Dinuclear Pathways for the Activation of Strained Three-Membered Rings

Abstract

Dinuclear, strain-induced ring-opening reactions of vinylaziridines and vinylcyclopropanes are described. The previously reported [NDI]­Ni2(C6H6) complex (NDI = naphthyridine–diimine) reacts with N-tosyl-2-vinylaziridine via C–N oxidative addition to generate a dinickel metallacyclic product. On the basis of this stoichiometric reactivity, the [NDI]­Ni2(C6H6) complex is shown to be a highly active catalyst for the rearrangement of vinylcyclopropane to cyclopentene. Notably, 2-phenyl-1-vinylcyclopropane undergoes regioselective activation at the less hindered C–C bond in contrast to the noncatalytic thermal rearrangement. DFT calculations provide insight into the ability of the Ni–Ni bond to stabilize key intermediates and transition states along the catalytic pathway.

Ni(NHC) Catalyzed Rearrangement of 1‐Acyl‐2‐vinylcyclopropanes: Tackling a Mechanistic Puzzle by Combined Experimental and Computational Studies

“…donor‐acceptor‐substituted vinylcyclopropanes, can react under much milder conditions, eventually promoted by Lewis acids . Furthermore, transition metal‐catalyzed rearrangements have been developed, most notably with Pd, Rh, Ni, Mo, Cr, Cu, Fe and more recently Ir complexes. However, in many cases transition metal catalysts need activated substrates, carrying at least two activating groups (EWG and/or EDG), heteroatoms, dienes, ene‐ynes or allenes.…”

[(NHC)NiIIH]‐Catalyzed Cross‐Hydroalkenylation of Cyclopropenes with Alkynes: Cyclopentadiene Synthesis by [(NHC)NiII]‐Assisted C−C Rearrangement

“…Here, a chemoselective insertion of 1 occurs (favored by ring‐strain release), followed by a fast regioselective insertion of 2 , rather than either a homo‐insertion of 1 (by steric interaction of 1 with bulky NHCs as depicted in Table ) or premature ring‐opening in Pd. After a (NHC)Ni II assisted vinylcyclopropane rearrangement at just 30 °C, as compared to Scheme c (alkenyl‐Ni II activation), (NHC)Ni II ‐allyl 1,3‐shift and catalyst regeneration by a β‐hydride elimination/transfer,– the desired product 3 is obtained. In this way, this HARC occurs without slow addition of the substrates, and fairly free from non‐selective oligomerization of either 1 or 2 .…”

Catalytic reductive [4 + 1]-cycloadditions of vinylidenes and dienes

“…This geometry permits the two Ni centers to stabilize the incipient allyl fragment as the diene undergoes migratory insertion (activation barrier = 7.1 kcal/mol). The resulting metallacycle 67 is structurally related to a Ni 2 azametallacycle that we previously characterized from a vinylaziridine ring-opening reaction (27). The final C-C reductive elimination is calculated to have a barrier of 23.4 kcal/mol and generates the product complex, which is thermodynamically favored over intermediate 67 by 13.9 kcal/mol.…”

“…1,1-Dichloroethylene provides a source of the parent vinylidene fragment (25)(26), yielding cyclopentene products with no substituents on the exocyclic methylene. Products containing tetrasubstituted alkenes are generated using ketone-derived 1,1-dichloroalkenes (27)(28). Representative 1-substituted (32), 2-substituted (33), 1,2disubstituted (34), and 1,3-disusbstituted (35) dienes were found to react efficiently with a model 1,1-dichloroalkene.…”