Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

Abstract

Our group has focused on the organometallic chemistry of rare-earth metals and actinides for a decade. By installing ferrocene diamide ligands at electropositive metal centers, we have been able to disclose unprecedented reactivity toward aromatic N-heterocycles, arenes, and other small molecules such as P 4 . Systematic studies employing X-ray crystallography, spectroscopy, cyclic voltammetry, and DFT calculations revealed that the ferrocene backbone could stabilize the electron-deficient metal through a donor-acceptor type interaction. Most noteworthy is that this interaction can be readily turned on or off by the addition or removal of a Lewis base. In addition to its flexible coordination, the redox active nature of the ferrocene backbone enabled us to explore redox-switchable transformations. The introduction of ferrocene-based ligands into organolanthanide chemistry not only helped to study intriguing fundamental problems but also led to fruitful chemistry including small molecule activation and controlled co-polymerization reactions.3

Geometry Change in a Series of Zirconium Compounds during Lactide Ring-Opening Polymerization

“…Our group has been interested in the redox switchable polymerization of lactide and its copolymerization with other monomers. [35][36][37][38][39][41][42][43][44][45][46][47][48][49][50] We were able to show that changing the oxidation state of iron in a ferrocene-based ligand modified the reactivity of a metal complex toward a certain monomer. Various 39 We became interested in studying a ferrocenederived Schiff base zirconium complex in order to simplify the ligand design and to compare its activity with that reported by Long et al for the corresponding titanium complex.…”

Neodymium(III) Complexes Capable of Multi‐Electron Redox Chemistry

“…Reactivity with 9,10‐phenanthrenequinone shows reduction to the corresponding potassium catecholate, thus this approach is effective for small molecule activation. Application of redox‐active ferrocene diamide ligands has also led to productive polymerization chemistry as demonstrated by Diaconescu and co‐workers with their redox switchable rare earth catalysts …”

Investigation of redox switchable titanium and zirconium catalysts for the ring opening polymerization of cyclic esters and epoxides

“…13 Many approaches [14][15][16] have been used to regulate the nature of polymerization reactions, such as allosteric, 17 chemical, [18][19][20] electrochemical, 21 photochemical, [22][23][24][25] and mechanochemical control. 26 Our group is focused on the use of chemical control via redox active systems [27][28][29][30][31][32][33][34][35] that switch between two stable oxidation states with different catalytic efficiencies. [36][37][38][39][40][41][42][43] Since one pre-catalyst is able to have two different active species, the cost of synthesizing two completely different metal complexes is eliminated.…”