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.