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Cross-electrophile coupling has emerged as an attractive and efficient method for the synthesis of C(sp2)–C(sp3) bonds. These reactions are most often catalyzed by nickel complexes of nitrogenous ligands, especially 2,2’-bipyridines. Precise prediction, selection, and design of optimal ligands remains challenging, despite significant increases in reaction scope and mechanistic understanding. Molecular parame-terization and statistical modeling provide a path to the development of improved bipyridine ligands that will enhance the selectivity of existing reactions and broaden the scope of electrophiles that can be coupled. Herein, we describe the generation of a computational lig-and library, correlation of observed reaction outcomes with features of the ligands, and in silico design of improved bipyridine ligands for Ni-catalyzed cross-electrophile coupling. The new nitrogen-substituted ligands display a fivefold increase in selectivity for product formation versus homodimerization when compared to the current state of the art. This increase in selectivity and yield was general for several cross-electrophile couplings, including the challenging coupling of an aryl chloride with an N-alkylpyridinium salt.
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Improved Synthesis of Chiral 1,4,7‐Triazacyclononane Derivatives and Their Application in Ni‐Catalyzed Csp 3 −Csp 3 Kumada Cross‐Coupling
Abstract Herein, we report four new chiral 1,4,7‐triazacyclononane (TACN) derivatives and their corresponding nickel(II) chloride complexes. All TACN ligands are bearing one chiral N‐substituent and two alkyl (methyl ortert‐butyl) N‐substituents, and we have developed a new synthetic method for the dimethyl‐substituted TACN derivative, in order to prevent the rotational isomers that hinder the cyclization reaction. The nickel complexes change their coordination geometry significantly depending on the steric bulk of the N‐alkyl substituents, from a dinuclear tris(μ‐chloro)dinickel complex to mononuclear Ni‐dichloride and Ni‐chloride complexes. These complexes were then employed in the alkyl‐alkyl Kumada cross‐coupling reaction and revealed that the more sterically hindered ligands produced more homocoupled product rather than the cross‐coupled product, while the mononuclear Ni‐dichloride complex exhibited significantly lower catalytic activity. These chiral complexes were also employed in enantioconvergent cross‐coupling reactions as well, to afford significant enantioenrichment. Overall, the least sterically hindered Ni complex yields the best yields in the alkyl‐alkyl Kumada cross‐coupling reaction among the four complexes investigated, as well as the highest enantioselectivity.
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- Award ID(s):
- 2155160
- PAR ID:
- 10478376
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Helvetica Chimica Acta
- Volume:
- 107
- Issue:
- 1
- ISSN:
- 0018-019X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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