Lanthanide(II) Complexes Supported by N,O‐Donor Tripodal Ligands: Synthesis, Structure, and Ligand‐Dependent Redox Behavior

Abstract

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O-donor tripodal ligands (tris(2-pyridylmethyl)amine (TPA), BPA(-) (HBPA=bis(2-pyridylmethyl)(2-hydroxybenzyl)amine), BPPA(-) (HBPPA=bis(2-pyridylmethyl)(3.5-di-tert-butyl-2-hydroxybenzyl)amine), and MPA(2-) (H2 MPA=(2-pyridylmethyl)bis(3.5-di-tert-butyl-2-hydroxybenzyl)amine) is reported. The X-ray crystal structures of the heteroleptic Ln(2+) complexes [Ln(TPA)I2 ] (Ln=Eu, Yb) and [Yb(BPA)I(CH3 CN)]2 , of the Ln(2+) homoleptic [Ln(TPA)2 ]I2 (Ln=Sm, Eu, Yb) and [Eu(BPA)2 ] complexes, and of the Ln(3+) [Eu(BPPA)2 ]OTf and [Yb(MPA)2 K(dme)2 ] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis-ligand complexes of Eu(3+) and Yb(3+) show that the metal center reduction occurs at significantly lower potentials for the BPA(-) ligand as compared with the TPA ligand. This suggests that the more electron-rich character of the BPA(-) ligand results in a higher reducing character of the lanthanide complexes of BPA(-) compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis-TPA complexes of Eu(2+) and Yb(2+) do not show any reactivity with heteroallenes, the [Eu(BPA)2 ] complex reduces CS2 to afford the first example of a lanthanide trithiocarbonate complex.

Electrogenerated Chemiluminescence and Electronic States of Several Organometallic Eu(III) and Tb(III) Complexes: Effects of the Ligands

“…Bond et.al. pointed out that E (Eu 3+/2+ ) of organometallic Eu(III) complexes depended on the kind of constituting ligands and solvent molecules, and such a dependence can be seen in several reports ,. The irreversibility of the first reduction wave of the Eu(III) complexes could be related to the distribution of the newly occupied MOs at the first reduction.…”

Coordination Environment-Controlled Photoinduced Electron Transfer Quenching in Luminescent Europium Complexes

“…The replacement of an amide donor with a carboxylate decreases the apparent reduction potential by ∼95 mV, from −554 mV for EuL4a MOM , to −638 mV for EuL3 MOM , to −747 mV for EuL2 MOM , to −839 mV for EuL1 MOM (vs NHS, Figure , bottom). Similar trends have been reported for europium complexes wherein hard oxygen or phenolate donors were replaced by softer amides, amines, or sulfur. ,,,,− Depending on the additional changes (e.g., in cavity size or overall charge) stemming from such substitutions, the apparent reduction potential of Eu­(III) shifted by 0.042–1.24 V. Amide methylation on all three coordinating arms leads to a decrease of ∼59 mV, from −554 mV for EuL4a MOM , −603 mV for EuL4b MOM , to −671 mV for EuL4c MOM , likely due to the stabilization of Eu­(III) through inductive effects (vs NHE, Figure S14).…”

CNRS Silver and Bronze Medals 2016 / Izatt–Christensen Award: H. F. Sleiman / Cram Lehn Pedersen Prize: I. Aprahamian

“…Nocton's research is focused on electron‐transfer studies in organolanthanide complexes containing redox noninnocent ligands, as well as the activation of small molecules. He is co‐author of reports in Angewandte Chemie on a nickel(III) complex bearing a tetradentate phosphasalen ligand, and in Chemistry—A European Journal lanthanide complexes containing N,O‐donor tripodal ligands …”