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

The reactivity of the monoanionic amidinate ligand [(CH3)(3)CNC(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)(3)CNC(Ph)NSi(CH3)(2)NC(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)(3)CNC(Ph)Si(CH3)(2)-N(C(CH3)(3))C(Ph)NSi(CH3)(2)NC(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)(3)CNC(Ph)NSiMe2NC(Ph)NHC(CH3)(3)Th(OH)(2)(Cl)](2)center dot(3) as bright red needles, exhibiting extremely short Th-OH bond distances (1.741(5) angstrom and 1.737(5) angstrom). 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.