Copper(I) Complexes Bearing the Pyrrole-Bridged S,N and N-Donor Ligands as Catalysts for the Tandem Hydroamination-Alkynylation: Effect of Anions on Product Formation

Abstract

The reaction between 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)pyrrole and thiophenol under heating conditions afforded the new ligand 2-(3,5-dimethylpyrazolylmethyl)-5-(phenylthiomethyl)pyrrole 2. The reaction of 2 with meta-chloroperbenzoic acid gave the sulfoxide 3 and sulfone 4 groups containing ligands. The reaction of 2 with copper(I) halides gave the binuclear complexes: [Cu(-X){-C4H3N-2-(CH2Me2pz)-5-(CH2SPh)-κ2¬¬-S,N}]2 (X = Cl, Br and I, 5-7) in high yields. Conversely, the analogous reaction of 4 with copper(I) halides yielded two types of complexes – three coordinate bi- and mononuclear of the type: [Cu(-Cl){C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}]2 8 and [CuX{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2], X = Br, 9 and I, 10. When the reaction was carried out in the presence of KPF6, the two coordinate complex [Cu{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2]PF6 11a was isolated; its BF4 analogue 11b was synthesized by the reaction of 8 with AgBF4. The structures of these complexes were determined by single crystal X-ray methods. These copper complexes catalyze the hydroamination-alkynylation reaction between several secondary amines, and alkyl, aryl terminal alkynes. Using 1 mol% of complexes 5-10 as catalysts, both the tri- and tetrasubstituted propargylamines were isolated. While phenylacetylene and different secondary amines afforded the corresponding trisubstituted propargylamines as the major products, alkyl terminal alkynes gave the tetrasubstituted products in excellent yields. The role of counter anion such as TfO, PF6, BF4, PO43 and Ph4B on product selectivity was also studied. When fluorinated anions TfO, PF6, and BF4 are present with copper complexes, the hydroamination-hydrovinylation product 1-aminodiene 23 was observed, which was not formed with PO43, Ph4B or halide ions. Specifically, the TfO and PF6 anions are in favor of formation of 23, while BF4 is in favor of the tetrasubstituted product as the major product. This has been further supported by the isolated copper(I) complexes containing PF6, and BF4 and by other specific reactions. Peaks for enamines and [LCu]+ species in HRMS spectra of reaction mixtures and the isolation of morpholinium copper(I) salt are in support of the proposed mechanism.