Mechanistic Insights into the Aerobic Copper(I)-Catalyzed Cross-Coupling of S-Acyl Thiosalicylamide Thiol Esters and Boronic Acids

Abstract

The Density Functional Theory (DFT) method is used to elucidate the nature of the active species and the mechanism of the aerobic CuI-catalyzed cross-coupling of S-acyl thiosalicylamide thiol esters and boronic acids reported previously (J. Am. Chem. Soc. 2007, 129, 15734–15735; Angew. Chem., Int. Ed. 2009, 48, 1417-1421). The energetically lowest isomer of the proposed active species [LC(O)R1]Cu-(O2)-Cu[LC(O)R1]2+, 2a, (where L = thiolatosalicylamide) is found to be I1(OO,OO) with a μ-η2:η2-peroxo Cu2O2-core, while its isomers I2(OO,OO) with a bis-(μ-O) Cu2O2-core and I3(OO,OO) with a (μ-η1:η1) Cu2O2-core lie only a few kcal/mol higher and separated by 4–7kcal/mol energy barriers. In all these isomers, the thiol ester is coordinated to the Cu-centers via its two O-ends. Isomers with (SO,OO) and (SO,SO) coordination modes of the thiol esters lie slightly higher and are separated with moderate energy barriers. We found the latter isomers to be vital for the reported CuI-templated cross-coupling of S-acyl thiosalicylamide thiol esters and boronic acids under aerobic conditions. The presence of an anion (halide, carboxylate modeled as formate) in the reaction medium is found to be necessary. Its coordination to the active catalyst I1(SO,SO) is the first step of the proposed anion-assisted transmetalation by boronic acid. Overall the transmetalation reaction requires 34.0 kcal/mol and is 24.0 kcal/mol exergonic. This conclusion is in reasonable agreement with available experiments. The C-C bond formation in the transmetalation product requires a 6.3 kcal/mol lower energy barrier and is highly exergonic.

Gas‐phase studies of copper catalyzed aerobic cross coupling of thiol esters and arylboronic acids

“…We note in passing that during our experiments, we have never observed complexes of copper containing oxygen atoms. In this respect, it has been suggested that the reaction may proceed via copper clusters with the [Cu 2 (μ‐η 2 :η 2 ‐O 2 ] 2+ or [Cu 2 (μ‐O 2 ] 2+ core . We have neither observed binuclear doubly charged copper complexes nor complexes containing oxygen atoms under the conditions of the present experiments.…”

“…In this respect, it has been suggested that the reaction may proceed via copper clusters with the [Cu 2 (μ-η 2 :η 2 -O 2 ] 2+ or [Cu 2 (μ-O 2 ] 2+ core. [46,54] We have neither observed binuclear doubly charged copper complexes nor complexes The spectrum is taken at room temperature and 1 h after mixing all reactants together. Note that this reaction mixture is in methanol only, and the results are thus different from the results in Table 1 Scheme 3.…”

Aerobic Copper-Catalyzed Organic Reactions

“…These reports include: reviews (Section I), 1149,1150,1151,1152 oxygenation of unactivated benzylic substrates (Section IIA.2), 1153,1154,1155 alkane oxidation (Section II.B), 1156,1157,1158 epoxidation of alkenes (Section II.C.2), 1159 oxidation difunctionalization of alkenes (Section II.C.3), 1160,1161,1162,1163,1164 cross coupling with alkynes (Section II.D.3), 1165 oxidation difunctionalization of alkynes (Section II.D.4), 1166,1167,1168 arene hydroxylation (Section II.E.1), 1169 reactions involving nucleophilic arenes (Section II.E.2), 1170 direction insertion of arenes (Section II.E.3), 1171,1172,1173,1174,1175 functionalization of acidic arene positionos (Section II.E.4), 1176,1177,1178 coupling of carbanion equivalents with boronic acids (Section III.C), 1179,1180,1181,1182,1183,1184,1185 alcohol oxidation (Section IV.A.1),1186,1187,1188,1189,1190,1191,1192,1193,1194,1195,1196,1197,1198,1199 tandem reaction with alcohol oxidation (Section IV.D), 1200,1201,1202,1203,1204,1205,1206,1207,1208 oxidation of aldehydes to amides (Section V.A), 1209 enolate oxiation without cleavage (Section V.C), 1210,1211 oxidative coupling of enolates (Section V.C.1), 1212 α-oxygenation of carboxylic acids (Section V.E), 1213 reaction of hydrazones (Section V.G), 1214 oxidation of hydrazones with cyclization (Section V.G), 12151216 reactions of enamines (Section VI.A), 1217,…”

Mechanistic Insight into the 2° Alcohol Oxidation Mediated by an Efficient CuI/L-Proline-TEMPO Catalyst—A Density Functional Theory Study

“…Then, we suppose that another 0 coordinates to 3,1 18 to form a binuclear Cu II species Cu 2 O 2 (19). For 19, three dominant bonding motifs are considered (side-on µ-η 2 :η 2 -peroxo, bis-µ-oxo-Cu III and trans end-on µ-η 1 :η 1 -superoxo) [45]. However, all the efforts to locate the binuclear Cu II species failed.…”