Abstract
We describe herein two alternative protocols to efficiently prepare difluoromethylgold(I) complexes bearing ancillary ligands with different electronic and steric properties. LAu–OX (X = H and t-Bu) species, formed in the presence of base, have been identified as intermediate complexes involved in these transformations. The application of these compounds as “CF2H transmetalation shuttles” from gold to palladium has been demonstrated in a Pd-catalyzed difluoromethylation reaction of aryl iodides, in which the Au-to-Pd transfer of “CF2H” is feasible under stoichiometric conditions. These findings will pave the way for catalytic manifolds in gold chemistry.
Highlights
We describe two alternative protocols to efficiently prepare difluoromethylgold(I) complexes bearing ancillary ligands with different electronic and steric properties
Ideal strategies are represented by single-metal-catalyzed difluoromethylation reactions performed on accessiblearyl halides and/or with inexpensive industrial raw materials as “CF2H” source, these processes are scant.[6]
Nucleophilic organometallic M−CF2H compounds have been used for this purpose. (NHC)Ag(CF2H) complexes were among the first bench-stable organometallic compounds of this type to be prepared and broadly used.5f,i,7 Later, Sanford and co-workers were able to isolate and characterize analogous (NHC)Cu(CF2H) complexes, and they further explored their reactivity with aryl electrophiles, both in stoichiometric and catalytic fashions.5d Very recently, isolable [(L)Pd(CF2H)X] complexes have been synthesized, and the stoichiometric transfer of the CF2H substituent to arenes was studied.5l Given the parallel reactivity exhibited by the coinage metals in many instances,[8] we wondered whether analogous L−Au−CF2H complexes could be prepared by selecting the appropriate ancillary ligands on gold
Summary
Patricia García-Domínguez − CINBIO, Universidade de Vigo, Departamento de Química Orgánica, 36310 Vigo, Spain; orcid.org/0000-0003-0522-4823; Email: patrigarcia@. Despite the fact that (p-CF3-Ph)Au−CF2H (10b) afforded traces of the transmetalation product, the electron-poor (p-F-Ph)3PAu− CF2H (11b) furnished 17b in 14% yield over the two steps. Gold complexes bearing electron-rich phosphines such as 4b, 5b, 6b, and 7b under the same reaction conditions delivered the desired product in yields ranging from 10 to 20%. Aryl iodides bearing electron-donating groups in the para-position were not suitable for this transformation, as shown by the detection of difluoromethylated product 18b in trace amounts. The presence of electron-withdrawing groups was beneficial for the reaction as demonstrated by the preparation of the CF2H-aryl derivatives 20b and 21b in 33 and 38% yield, respectively, which represent the best results achieved for this transformation.
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