Synthesis, Structure, and Catalytic Activity of Pd(II) Complex of Calixoxasmaragdyrin

Abstract

The palladium­(II) complex of calixoxasmaragdyrin was prepared in 80% yield by treating the free base calixoxasmaragdyrin with PdCl₂ in CH₃CN at reflux temperature. The crystal structure solved for Pd­(II) calixoxasmaragdyrin indicates that the calixoxasmaragdyrin macrocycle is highly distorted and attained a boat shaped structure. The Pd­(II) ion is coordinated to four pyrrolic nitrogens in square planar fashion, and it is placed at ∼0.138 Å above from the four coordinating pyrrole nitrogens plane (N1N2N3N4). The Pd–N bond lengths are inequivalent, and the Pd­(II) ion is positioned more toward the dipyrromethane moiety of calixoxasmaragdyrin. The complex shows one broad absorption band at 477 nm and is not very stable under redox conditions. The Pd­(II) calixoxasmaragdyrin showed good catalytic activity in the Suzuki–Miyaura cross coupling reactions