Actinide Amidinate Complexes with a Dimethylamine Side Arm: Synthesis, Structural Characterization, and Reactivity

Abstract

The reactivity of monoanionic amidinate ligands containing a dimethylamine side arm with variable lengths of the linker chain and aromatic substituents of the ipso carbon atom was investigated for the early actinides thorium and uranium. The bis(amidinate) actinide complexes obtained were structurally characterized, displaying a coordination of both dimethylamine nitrogen atoms to the respective metal center, allowing for a fine tuning of the reactivity of the complex by manipulation of the coordination environment around the metal center. The reactivity of the actinide amidinate complexes was studied in the catalytic ring-opening polymerization of ε-caprolactone.

Homoleptic U(iii) and U(iv) amidate complexes

“…Cyclopentadienyl (Cp) derivatives are often used to provide steric support around the uranium center, but a large amount of research has been directed towards developing actinide complexes using alternative ligand systems, 18,26,32 including carbenes, 33,34 carboxylates, 28,29,35 and amidinates. [36][37][38][39][40] Interestingly, amidates, which can be seen as hybrids of carboxylates to amidinates, have been only sparsely studied as ligands in actinide chemistry. 24,41 In contrast, amidate complexes of group IV metals have been investigated for a variety of applications.…”

Catalytic Organic Transformations Mediated by Actinide Complexes

“…The first step of the mechanism includes the coordination of ε-caprolactone to the thorium center, followed by a displacement of The actinide bis(amidinate) systems ( Figure 8) with functionalized side arms on the amidinate ligand have shown to promote the ROP of ε-caprolactone, furnishing linear polymers with narrow molecular weight distributions [90,91]. A systematic study of a series of bis(amidinate) thorium and uranium complex (21)(22)(23)(24)(25) with a dimethylamine side arms has shown an increase in the catalytic activity in the order 23 > 24 > 25 > 21 > 22 [91]. Hence, the thorium complexes 23-25 are more active than their uranium analogues 21-22, and complexes with a phenyl at the ipso-position (21, 23-24) are more active than the analogous compounds with a pyridyl moiety at the ipso-position (22 and 25).…”

“…A subsequent nucleophilic attack of an incoming monomer on complex A, gives the open chain intermediate B, which is the rate determining step of the reaction. Further insertion of ε-caprolactone units into the An-O bond of B, furnishes compound C, which after the elimination of the polymer (D) regenerates the active catalyst A[90,91]. Also actinide inclusion complexes have been recently shown to operate via the mechanism depicted in Scheme 22[92].…”

Benzimidazolin-2-iminato Hafnium Complexes: Synthesis, Characterization, and Catalytic Addition of Alcohols to Carbodiimides

“…During the past decade, our group has been interested in non-Cp ancillary ligands. In particular, we have been attracted by chelating amido-type benzamidinate ligands. ,,,,− Benzamidinate ligands can be deemed steric equivalents of Cp or Cp* (Cp = C 5 H 5 ; Cp* = C 5 Me 5 ) moieties; however, they retain distinctive electronic properties. ,,,− The activation of the complexes containing these systems has provided crucial insights into the tailoring of new ancillary ligands, which are isolobal to the cyclopentadienyl ligands yet possess a higher level of steric control. Imidazolin-2-iminato ligands are among the leading fascinating examples of such non-Cp ancillary ligands, as presented in Scheme A. − A simple and general method for the synthesis of this class of 2-iminoimidazoline N -heterocyclic N-donor ligands, which behave as 2σ, 4π-electron donors, has been already introduced in the literature. − …”