Eugenol-Derived Bipyridine Ligand Scaffolds: Design, Metal Coordination, and Catalytic Applications in Cyclic Carbonate Synthesis

High Resolution Image Download MS PowerPoint Slide This work reports the synthesis of bis(4-allyl-2-methoxyphenyl) [2,2′-bipyridine]-5,5′-dicarboxylate (bpyEu) ( 1 ) derived from the conjugation of 2,2′-5,5′-dicarboxylic acid with the natural product eugenol. This hybrid bis-eugenol ligand integrates π-conjugated bipyridine with a phenolic ether moiety. After successful multigram synthesis of this bipyridine ligand 1, its metalation was explored by reacting with M(CO) 5 X, where M = Mn, Re and X = Br, Cl, resulting in the formation of M(bpyEu)(CO) 3 X, where M = Mn, X = Br ( 2 ); M = Re, X = Cl ( 3 ). The hybrid ligand ( 1 ) and its transition metal complexes 2 and 3 were thoroughly characterized by different spectroscopic techniques, such as NMR and Fourier transform infrared (FTIR) spectroscopy, which confirmed their formation, and their molecular structures were established using single-crystal XRD in the solid state and mass spectrometry in solution. The electrochemical behaviors of 2 and 3 were further investigated by cyclic voltammetry. Compound 2 exhibited reversible reductions at −0.828 V and −1.493 V with an irreversible oxidation at +1.44 V, whereas complex 3 displayed a reversible reduction at −0.66 V and −1.08 V along with an irreversible metal-centered oxidation at +1.69 V. Further, we used bis-eugenol-based ligand 1 as an organocatalyst for the cycloaddition of CO 2 with epoxides, which showed excellent selectivity for cyclic carbonate synthesis without the need for a cocatalyst. The catalytic activities of complexes 2 and 3 were also evaluated for cyclic carbonate synthesis, which revealed that these metal complexes lacked the catalytic ability for this transformation.