Dimethylsilyl bis(amidinate)actinide complexes: synthesis and reactivity towards oxygen containing substrates

Abstract

The reactivity of the monoanionic amidinate ligand [(CH₃)₃CNC(Ph)NSiMe₂NC(Ph)–NHC(CH₃)₃]Li (1) with a silyl amido side arm towards the early actinides, uranium and thorium, was investigated. While the salt metathesis reaction with ThCl₄(thf)₃ afforded the bis(amidinate)thorium(IV) dichloride complex [(CH₃)₃CNC(Ph)NSi(CH₃)₂NC(Ph)–NHC(CH₃)₃]ThCl₂ (2) in high yield, the reaction of ligand 1 with UCl₄ leads to a Lewis acid supported nucleophilic attack of an incoming ligand unit, yielding the trichloro uranium complex [(CH₃)₃CNC(Ph)Si(CH₃)₂–N(C(CH₃)₃)C(Ph)NSi(CH₃)₂NC(Ph)N–(C(CH₃)₃]UCl₃ (4). The exposure of in situ formed complex 2 to wet THF solutions (<1% w of water), gave the mono(amidinate)Th(IV)(chloro)(bis-hydroxo) dimeric complex [(CH₃)₃CNC(Ph)NSiMe₂NC(Ph)NHC(CH₃)₃Th(OH)₂(Cl)]₂·(3) as bright red needles, exhibiting extremely short Th–OH bond distances (1.741(5) Å and 1.737(5) Å). The reactivity of the thorium complex 2 in the ring opening polymerization (ROP) was studied, showing high activity. Thermodynamic and kinetic measurements were performed to shed light on the mechanism for the ROP.