Products Cited in Publications Worldwide Synthesis and Characterization of Low-Spin D6 Polypyridyl Complexes: Manipulation of Excited-State Electronic Structure Through Ligand Design

Synthesis and Characterization of Low-Spin D6 Polypyridyl Complexes: Manipulation of Excited-State Electronic Structure Through Ligand Design

Jonathan Taylor Yarranton

Abstract

lron(ll) polypyridyl chromophores are among one of the most promising earth-abundantalternatives to ruthenium-based complexes in the realms of photo-redox catalysis and solar energyharvesting. The biggest hurdle to their implementation is the sub-150 fs metal-to-ligand chargetransfer (MLCT)excited-state lifetime which limits their implementation in diffusion-imitedprocesses. The main way in which researchers have approached this problem is by attempting toinvert the ligand-field (LF) and MLCT manifolds by increasing the donor ability of the ligandsemployed. To better understand the destabilizing nature ofthe ligands employed, a series ofCo(ll)complexes were synthesized as an isoelectronic stand-in for Fe(ll) to measure the LF transitions ofvarious polypyridyl ligands as well as the first carbene ligand coordinated to Fe(ll) to detemmine therelevant ligand-field parameters and assess the splitting observed. These results indicate thatpolypyridyl complexes do not impose a strong enough LF to destabilize them above the MLCT. Tothat end, we synthesized a series of simple bis pyridinium-based polypyridyl ligands with increasedsigma-donor ability compared to the widely used carbene systems, achieving a MLCT lifetime of18 ps, a 2-fold increase from the first reported tetra-carbene system. A final thrust was to betterunderstand the unique MLCT manifold of [Fe(depp)2]+(where depp is 2,6-di(2.carboxypyridyl)pyridine) using symmetric n-substitutions. With this method, we were able tosynthetically deconvolute the MLCT spectrum and selectively enhance different transitions basedupon the substitution pattem. The computational insights gleaned can now guide new promisingligands in this family ofcomplexes.

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A35972218511-71-298%

4,4'-Dibromo-2,2'-bipyridine

755.0/100g

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