Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes

Abstract

Actinide complexes of a small-cavity, dipyrrolide macrocycle exhibit unusual bent metallocene-type binding, or bis(arene)-type binding, or both at once in a di-uranium adduct.

Organometallic neptunium(III) complexes

“…This O-C bond cleavage is common for reduced electropositive metal complexes, and supports the assignment of a reactive Np II centre in 3a. We have previously observed the double metalation of L Ar from the treatment of Th IV (L Ar ) complexes with either reductants or non-nucleophilic bases 16 , but the only occasion on which we have observed a An 3+ cation to reside in the cavity provided by the two pyrrolides (rather than the two arenes) is in the di-U III adduct, U III 2 I 4 (L Ar ) 16 . In this latter case, the 180 ligand undergoes a significant strain-energy penalty from the incorporation of two metal cations.…”

“…Small, black plate-shaped crystals of 3a isolated from these solutions gave only weak diffraction. bound in the 'metallocene-type' geometry provided by the two η 5 -bound pyrrolide groups 16 . A dimer is formed through asymmetric methoxide bridging which has presumably arisen from the cleavage of dme.…”

“…A desire to better understand the subtlest actinide π-and δ-symmetry 60 bonding interactions has led us to the flexible macrocycle H 2 L Ar trans-calix [2]benzene [2]pyrrole 15 , which can geometrically and electronically mimic two cyclopentadienyl ions i.e. bis(η 5 -pyrrolyl), or a bis(η 6 -arene) sandwich form 16 . Hybrid density functional theory (DFT) calculations found significant covalent bonding in both binding modes in the di-U III adduct 16 .…”

“…bis(η 5 -pyrrolyl), or a bis(η 6 -arene) sandwich form 16 . Hybrid density functional theory (DFT) calculations found significant covalent bonding in both binding modes in the di-U III adduct 16 . We have also used non-aqueous Np III iodides 17 to make magnetically coupled U III and Np III complexes that we could not structurally characterise 18 .…”

Uranium(III) Coordination Chemistry and Oxidation in a Flexible Small-Cavity Macrocycle

“…1 An alternative and very successful strategy has been the use of a single trianionic ligand framework to stabilize and coordinatively saturate the U(III) center while leaving a reactive pocket at the metal, with which to bind small molecules. 3 The latter complex makes use of stabilizing, π-symmetry bonding interactions 5 between the individual U(III) centers and either the two arenes (A, Chart 1) or the two pyrrolide (B, Chart 1) 6π-electron centers in the dinucleating macrocycle, and is an extremely rare example of a complex with two different U(III) coordination environments in the same compound. The degree of covalency in U-L bonding in both [U(L)I] and [U 2 I 4 (L)] was calculated, it was found that there was more covalent character to the U-pyrrolide bonding than to the U-arene bonding.…”