A Dinickel Catalyzed Cyclopropanation without the Formation of a Metal Carbene Intermediate

Abstract

(NDI)Ni 2 catalysts (NDI = naphthyridine-diimine) promote cyclopropanation reactions of 1,3-dienes using (Me 3 Si)CHN 2 .Mechanistic studies reveal that ametal carbene intermediate is not part of the catalytic cycle.T he (NDI)Ni 2-(CHSiMe 3)complex was independently synthesized and found to be unreactive toward dienes.B ased on DFT models,w e propose an alternative mechanism that begins with aN i 2mediated coupling of (Me 3 Si)CHN 2 and the diene.N 2 extrusion followed by radical CÀCb ond formation generates the cyclopropane product. This model reproduces the experimentally observed regioselectivity and diastereoselectivity of the reaction.

Combined Experimental and Computational Study of Ruthenium N-Hydroxyphthalimidoyl Carbenes in Alkene Cyclopropanation Reactions

“…Computational investigations have provided more detailed information on these pathways 9 , 10 and some exceptional alternatives. 11 In the inner-sphere mechanism, a metallacyclobutane intermediate 12 is formed upon a [2 + 2] cycloaddition between the carbene and the olefin ligands. 9 The outer-sphere mechanism, on the other hand, involves intermolecular reaction with the olefin either in a single step or via radical intermediates.…”

“… 10 More recent computational work has focused on catalysts that promote the outer-sphere mechanism, employing bulky ligands or dimeric metal species. 11 , 13 Mechanistic studies on simpler catalysts of the Ru-Pheox type are, however, still rather scarce. 14 While previously studied copper 7 and rhodium 8 catalysts have only one or two coordination sites available, the situation is greatly complicated in the case of Ru-Pheox ( 2 ) due to its octahedral C 1 -symmetric environment with four inequivalent positions that could lead to different intermediates (see Scheme 1 A).…”