Abstract: Redox-active ligands (RAL) offer a number of opportunities to the coordination chemistry. They can actively participate in the reactions of complexes, donating or accepting electrons to/from the metal center, thus influencing a coordinated substrate. Quinones and their derivatives are ones of the most popular RALs. They are conveniently synthesized and provide lots of possibilities for functionalization, to tune their donor and steric properties. A great part of quinone chemistry has been investigated for the complexes of late transition metals, and a number of useful properties have been found, such as redox isomerism, catalytic activity, magnetic bistability and environment-dependent behaviour. Complexes with typically oxophilic elements, early TM or lanthanides (Ln), have been less studied. Combination of RAL with lanthanide cations could lead to complexes with unusual for lanthanide compounds redox activity, as well as with magnetic or photophysical properties depending on the redox state of the ligand. We intended to find good synthetic procedures of Ln complexes with quinone-based RALs in order to study their structures and reduction properties. Three o-quinone derivatives of different geometry were used. 3,6-Di-t-butyl-o-benzoquinone (3,6-Q; its charged forms 3,6-SQ–, 3,6-Cat2–) is a bulky RAL, which was popularized by the works of G. A. Razuvaev, G. A. Abakumov and V. K. Cherkasov. 9,10-Phenanthrenequinone (phenQ) is its narrower analog, which should allow closer packing of the ligands. An iminoquinone based on 3,5-Q, 4,6-Di-t-butyl-N-(2,6-di-isopropylphenyl)-o-iminobenzoquinone (dippIQ, dippISQ–, dippAP2–), has a bulky N-aryl donor group, which largely influences the coordination geometry around the central atom. The quinones were either reduced by lanthanocenes ([LnCp*2(thf)2], Ln = Sm, Yb, Eu) or by other strong reductants (K, KC8) directly in the coordination sphere of Ln cations. Geometry and composition of the complexes predictably depend on the bulkiness of the ligand. Still, some very unexpected consequences of certain RAL-Ln combinations have been discovered, such as dependence of resultant structures on the reduction properties of the Ln2+ cation; aggregation of flat phenQ ligands due to π-stacking, leading to tetranuclear complexes, coordination isomers and oligomers; radical-mediated reduction of S8 by dippAP2– complexes resulting in different polysulfides, and formation of heteroligand tris-radical-anionic complexes. Peculiarities of interactions in Ln-RAL complexes will be discussed.

Cite: Konchenko S.N. , Sinitsa D.K. , Pushkarevsky N.A.
Lanthanide complexes with quinone-based redox-active ligands
HIGH-SPIN MOLECULES AND MOLECULAR MAGNETS 09-14 Jul 2023