Synthesis of Nickel(I)–Bromide Complexes via Oxidation and Ligand Displacement: Evaluation of Ligand Effects on Speciation and Reactivity

Abstract

Nickel's +1 oxidation state has received much interest due to its varied and often enigmatic behavior in increasingly popular catalytic methods. In part, the lack of understanding about Ni I results from common synthetic strategies limiting the breadth of complexes that are accessible for mechanistic study and catalyst design. We report an oxidative approach using tribromide salts that allows for the generation of a well-defined precursor, [Ni I (COD)Br] 2 , as well as several new Ni I complexes. Included among them are complexes bearing bulky monophosphines, for which structure−speciation relationships are established and catalytic reactivity in a Suzuki−Miyaura coupling (SMC) is investigated. Notably, these routes also allow for the synthesis of well-defined monomeric t-Bu bpy-bound Ni I complexes, which has not previously been achieved. These complexes, which react with aryl halides, can enable previously challenging mechanistic investigations and present new opportunities for catalysis and synthesis.

Nickel-Catalyzed O-Arylation of Primary or Secondary Aliphatic Alcohols with (Hetero)aryl Chlorides: A Comparison of Ni(I) and Ni(II) Precatalysts

“…Previous work from our group focusing on C–N cross-coupling supports the feasibility of (DalPhos)Ni 0/II catalytic intermediates, in keeping with studies from others regarding (bisphosphine)Ni cross-couplings (e.g., C–N, C–S, and C–C). While we have shown that under some circumstances it is possible to achieve productive C–N cross-coupling catalysis commencing from (DalPhos)Ni I species, , it is unclear if turnover commences directly from (DalPhos)Ni I in these scenarios or whether redox events (e.g., dis/comproportionation) precede productive catalysis. , …”

“…While we have shown that under some circumstances it is possible to achieve productive C−N cross-coupling catalysis commencing from (DalPhos)Ni I species, 17,21 it is unclear if turnover commences directly from (DalPhos)Ni I in these scenarios or whether redox events (e.g., dis/comproportionation) precede productive catalysis. 22,23 With the aim of taking the first steps toward establishing a better understanding of our newly developed C−O crosscoupling chemistry, we initiated a study comparing the catalytic abilities of (bisphosphine)Ni I and (bisphosphine)Ni II precatalysts [Figure 1; bisphosphine = DalPhos or 1,1′bis(diphenylphosphino)ferrocene (DPPF)], both to assess their practical utility and to gain preliminary information regarding the viability of Ni(0/II) versus Ni(I/III) cycles.…”

Trendbericht Anorganik 2024: Nebengruppen, Bioanorganik und Koordinationschemie

“…Dabei erwiesen sich niedrigkoordinierte Komplexe als überraschend unreaktiv. 21) Hartwig und Mitarbeiter:innen widmeten sich bei Kupfer der oxidativen Addition von Elektrophilen. Sie wiesen erstmals einen Additionsprozess nach, bei dem eine Organokupfer(III)spezies entsteht (Abbildung 8C).…”

Comproportionation and disproportionation in nickel and copper complexes

“…The authors proposed that the inclusion of 1,5cyclooctadiene (L7, COD) results in (L7)Ni(I)X Ni-8 (X = I, Br), 69 the identity of which has been recently supported by the isolation of [(COD)Ni-Br] 2 and [(L7) 2 Ni][Al(ORF) 4 ] Ni-9 (ORF = OC(CF 3 ) 3 ). 70,71 Introduction to anionic ligand disproportionation In situ reduction by anionic ligand disproportionation has been a widely reported method to access Ni(0) and Ni(II) species from R-Ni(II)X organometallic complexes (R = allyl, aryl, alkyl) which then can react by comproportionation to afford Ni(I) complexes. Alternatively, such Ni(I) intermediates can be accessed via oxidative addition of an organic halide to Ni(0)L n given that after ligand disproportionation and reductive elimination, Ni(0) and Ni(II) species are generated in equimolar ratios.…”