Synthesis and coordination chemistry of multidentate ligands based on nitrogen-containing heterocyclic phenanthridine moieties
This project explored the synthesis of bi-functional neutral donor ligands using pi-extended phenanthridine system which can stabilize the late transition metals. My interest would be the phenanthridine ring of 14 pi-electron polycyclic heteroaromatic system, which is the building block of my ligands and the properties of this extended aromatic system while binding with late transition metals and comparing with smaller congener quinoline precursor for understanding the effect of site dependent pi extension. The application and properties of designed metal complexes have been extensively studied. The study of using pi-extended phenanthridine as a ligand and its metal complexes would open a new window of opportunities. A synthetic route to bromo functionalization of benzo-fused N-heterocyclic phenanthridine, enabling the constructions of both phosphinophenanthridine and NHC carbene-phenanthridine have been devised, which are heterobifunctional Lewis base containing both phosphine/carbene and phenanthridine donors. The coordination chemistry for both phosphine/carbene ligands with ions of late first-row transition metals has been explored. 4-Bromophenanthridine was synthesized by Suzuki cross-coupling/condensation, 6-substitution was conducted by reaction between phenanthridinone and phosphine(V) oxyhalide. The installation of phosphine was directed by lithium-halogen exchange of 4-bromophenanthridine. The carbenes were placed by the reaction between 6-halophenanthridine and corresponding imidazole in high temperature. A series of halide bridge Cu complexes were synthesized using phosphino-phenanthridine ligand to check the effect of site selective pi-extension on emission property by comparing with smaller congener quinoline based Cu complexes. Further study leads to design of sterically encumbered phenanthridine for diminishing the excited state geometric orientation. A relative effect of counterion in solid-state emission lifetime has also been studied. A group of octahedral d8 metal complexes were synthesized by using both phosphine/carbene ligands to study the metal to ligand charge transfer and its lifetime. The potential of these complexes for use in the field of photosensitizer was also discussed. Phosphino ligand based Fe complexes have been synthesized and their use in the filed of hydrogenation catalysis has also been discussed.