Oxidation of Ni(II) to Ni(IV) with Aryl Electrophiles Enables Ni-Mediated Aryl–CF₃ Coupling

Abstract

This communication describes the synthesis and reactivity of Ni(IV)(aryl)(CF3)2 complexes supported by trispyrazolylborate and 4,4'-di-tert-butylbipyridine ligands. We demonstrate that isolable Ni(IV) complexes can be accessed under mild conditions via the oxidation of Ni(II) precursors with S-(trifluoromethyl)dibenzothiophenium triflate as well as with diaryliodonium and aryl diazonium reagents. The Ni(IV) intermediates undergo high yielding aryl-CF3 bond-forming reductive elimination. These studies support the potential viability of Ni(IV) intermediates in nickel-catalyzed coupling reactions involving diaryliodonium and aryldiazonium electrophiles.

Photoinduced Cobalt(III)−Trifluoromethyl Bond Activation Enables Arene C−H Trifluoromethylation

“…Fori nstance,C À CF 3 reductive elimination from high-valent electrophilic Group 10-11 metals continues to garner significant interest. [19,21,[31][32][33][34][35][36][37][38] Baker and co-workers are using fluoride abstraction from CoÀCF 3 complexes to circumvent the stability of Co perfluoroalkyl complexes. [39,40] CobaltÀalkyl complexes are among the most studied organometallic bonds.B iological activity in B 12 -dependent mutases is predicated on facile,reversible Co À Chomolysis.…”

Trifluoromethylation of a Well‐Defined Square‐Planar Aryl‐NiII Complex involving NiIII/CF3. and NiIV−CF3 Intermediate Species

“…[9] The slower reactivity observed with 5 OTf suggests a lower stability of the high oxidation state on the metal when tertiary amines are used. [23] However, the putative aryl-Ni IV intermediated species could not be detected by 1 H NMR spectroscopy even at -40ºC, suggesting that this putative intermediate is highly reactive ( Figure S6).…”

“…The uncontrolled side reactions of in situ generated Ni I species has been discussed very recently by Sanford and coworkers. [21] Since Ni IV species were reported to undergo reductive elimination with nucleophiles, [5,9] we tested 2e-oxidants such as F + reagents (N-fluoro-2,4,6-trimethylpyridinium triflate (NFTPT), Selectfluor®), [22] but again multiple decomposition pathways occurred. Strikingly, reaction of 1 OTf and 5 OTf complexes with CF 3 + sources (5-(trifluoromethyl)dibenzothiophenium trifluoromethanesulfonate (TDTT), 3,3-Dimethyl-1-(trifluoromethyl)-1,2-benziodoxole (Togni reagent)) afforded the quantitative formation of L 1 -CF 3 and L 5 -CF 3 products.…”

A Ni(iii) complex stabilized by silica nanoparticles as an efficient nanoheterogeneous catalyst for oxidative C–H fluoroalkylation

“…Interest in nickel compounds of higher oxidation states (III, IV) has now grown considerably, especially given the prospects of using them in oxidation catalysis [10][11][12][13][14][15] . Although the first reports of complexes and salts of nickel in oxidation states (III) and (IV) appeared a relatively long time ago [16][17] An attractive goal would be to obtain nickel derivatives in higher oxidation states, stabilized by a special environment so that they are highly effective in catalytic reactions, meanwhile easy to handle as well, and their separation from the reaction mixture, suitable for regeneration and reactivation.…”