Cross‐Coupling through Ag(I)/Ag(III) Redox Manifold

Abstract

In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e À redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through Ag I /Ag III redox catalysis (i. e. CEL coupling), namely: i) easy Ag I /Ag III 2e À oxidation mediated by air; ii) bpy/phen ligation to Ag III ; iii) boron-to-Ag III aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-Ag III -CF 3 ] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K] + [Ag III (CF 3 ) 4 ] À (K-1), [(bpy)Ag III (CF 3 ) 3 ] (2) and [(phen)Ag III (CF 3 ) 3 ] (3), is described. The utility of 3 in crosscoupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [Ag III (aryl)(CF 3 ) 3 ] À intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.

Ligand-free nickel catalyzed perfluoroalkylation of arenes and heteroarenes

“…Since the synthesis of 1 involves the use of AgF, minute residue of silver may remain in the nickel complex product; thus silver salts were evaluated as possible contributors to catalysis. 63 However, silver fluoride and silver triflate (entry 8-11) under catalytic conditions afforded 26% and 0% yields respectively for 10 mol% silver, showing only a 56% yield of product if 100 mol% of silver was used. The control reaction in the absence of 1 afforded only 6% of pentafluoroethylated product (entry 14), indicating that 1 is a necessary catalyst, and that some nickel and silver species (entries 6, 7, 11-13) effectively shut down this background reaction.…”

“…Since the synthesis of 1 involves the use of AgF, minute residue of silver may remain in the nickel complex product; thus silver salts were evaluated as possible contributors to catalysis. 63 However, silver fluoride and silver triflate (entry 8–11) under catalytic conditions afforded 26% and 0% yields respectively for 10 mol% silver, showing only a 56% yield of product if 100 mol% of silver was used.…”

Electrophilicity of neutral square-planar organosilver(iii) compounds

“…It would therefore be advisable to take it into account when trying to trace reliable reaction mechanisms, as this might lead to a better understanding of the chemical processes. Compound 2•py bears an interesting relationship with (CF 3 ) 3 Ag(bpy), 6 since the two pyridine rings are detached in the former, whereas they are linked in the latter. A detailed comparison of their structures is therefore in order.…”

“…4 Two additional kinds of molecular compounds have been isolated with bidentate ligands: the dithiolate complex (CF 3 ) 2 Ag(S&S) (S&S = diethyldithiocarbamate) of unknown structure 5 and the five-coordinate (CF 3 ) 3 Ag(N&N) compounds, where N&N = bpy or phen (Chart 1c). 6,7 In this work, neutral Ag( iii ) complexes stabilised with just monodentate ligands are exemplified in the solvento-complex (CF 3 ) 3 Ag(NCMe) ( 1 ) and some of its derivatives with Group 15 donor ligands. Evidence for substantial electrophilic character at the metal centre is also given.…”

A Five‐Coordinate Compound with Inverted Ligand Field: An Unprecedented Geometry for Silver(III)

“… [17] No such rearrangement processes were observed working with the homologous gold system. [18] Upon chlorination under the indicated conditions, the 19 F NMR signal of the starting product A (δ F =−25.6 ppm) [5a] is downfield shifted to δ F =−24.54 ppm (Figure S4). More importantly, the 2 J ( 109 Ag, 19 F) coupling constant undergoes a dramatic reduction from 100.7 Hz in A to 14.0 Hz in 1 a .…”