An Actinide Complex with a Nucleophilic Allenylidene Ligand

Area of Science:

• Organometallic Chemistry
• Thorium Chemistry
• Ligand Design

Background:

• Cyclopropenyl compounds are strained three-membered rings.
• Thorium organometallics offer unique reactivity due to accessible f-orbitals.
• Allenylidene ligands are versatile building blocks in organometallic synthesis.

Purpose of the Study:

• To investigate the reactivity of a thorium cyclopropenyl complex.
• To synthesize and characterize novel thorium allenylidene complexes.
• To explore the electronic structure and bonding in these thorium complexes using DFT.

Main Methods:

• Reaction of [Cp3Th(3,3-diphenylcyclopropenyl)] with lithium diisopropylamide (LDA).
• Isolation and characterization of thorium allenylidene complexes and their derivatives.
• Density Functional Theory (DFT) calculations for electronic structure analysis.

Main Results:

• Cyclopropenyl ring opening of [Cp3Th(3,3-diphenylcyclopropenyl)] with LDA yielded the thorium allenylidene complex [Li(Et2O)2][Cp3Th(CCCPh2)] ([1]).
• Complex [1] underwent dimerization to form [Cp2Th(μ:η1:η3-CCCPh2)]2 (2) and reacted with MeI and benzophenone to yield thorium acetylide and tetraphenylbutatriene, respectively.
• DFT calculations confirmed significant electron delocalization in the allenylidene ligand and agreement with experimental 13C NMR shifts, indicating spin-orbital effects from Th 5f orbitals.

Conclusions:

• Thorium cyclopropenyl complexes can be effectively transformed into thorium allenylidene complexes.
• The thorium allenylidene ligand exhibits rich reactivity towards electrophiles and undergoes dimerization.
• DFT studies provide valuable insights into the electronic structure and bonding of these novel thorium complexes.