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Mixed sandwich thorium complexes incorporating bis(tri-isopropylsilyl)cyclooctatetraenyl and pentamethylcyclopentadienyl ligands: synthesis, structure and reactivity

2015-03-09T10:32:01Z

The Th(IV) mixed-sandwich halide complexes Th(COTTIPS2)Cp*X (where COTTIPS2 = 1,4-{SiiPr3}2C8H6, X = Cl, I) have been synthesised, and structurally characterised. When Th(COTTIPS2)Cp*I is reduced in situ in the presence of CO2, a mixture of dimeric carboxylate and oxalate complexes {Th(COTTIPS2)Cp*}2(μ-κ1:κ2-CO3) and {Th(COTTIPS2)Cp*}2(μ-κ2:κ2-C2O4) are formed, possibly via a transient Th(III) species. Th(COTTIPS2)Cp*Cl is readily alkylated to yield the benzyl complex Th(COTTIPS2)Cp*CH2Ph, which reacts with CO2 to form a carboxylate and with H2 to form a hydride; the latter inserts CO2, giving the bridging formate complex {Th(COTTIPS2)Cp*(μ-κ1:κ1-O2CH)}2.

The activation of carbon oxides by low valent group IV and thorium complexes

2012-05-31T13:23:52Z

Following discoveries in our laboratory that mixed-ring uranium(III) complexes reductively couple CO to produce new C-C bonds and transform this small molecule into potentially useful small organic things, further research has taken place into the synthesis, characterisation and reactivity of the zirconium, hafnium and thorium analogues. The first part of this thesis describes the preparation of the novel zirconium(IV) and hafnium(IV) mixed-sandwich chloride complexes using sterically demanding cyclopentadienyl and cyclooctatetraenyl ligands, and their subsequent reduction into the desired low valent M(III) compounds.

The second part considers the reaction between carbon oxides and three different zirconium(III) complexes in which differently substituted cyclopentadienyl ligands are employed. Reaction with CO generated two novel complexes that displayed C-C bond formation, with the products influenced by the sterics of the systems. Reaction with
CO2 produced products resulting from reduction and/or reductive disproportionation of CO2, which were independent of the steric bulk of the cyclopentadienyl ligand.

The third and final part of the thesis considers the synthesis of two novel mixed-ring thorium(IV) halide species, before a description of their in situ reduction in the presence of CO2 to yield products different to those previously described in this work. The reactivity illustrated here demonstrates a new approach to the reductive coupling of CO via characterised zirconium(III) complexes and provides insight into the reactivity of a
transient thorium(III) sandwich complex.

Mixed-sandwich complexes of zirconium(III) and hafnium( III): Potential analogues of [U(eta-C8H6{(SiPr3)-Pr-i-1,4}(2))(eta-Cp*)] for cyclooligomerisation of CO

2012-02-06T19:22:57Z

Reaction of ZrCl4 or HfCl4 with 2 equivalents of K-2(COT{(SiPr3)-Pr-i-1,4}(2)), followed by in situ treatment of the resultant sandwich complexes M(COT{(SiPr3)-Pr-i-1,4}(2)) with a further equivalent of MCl4 affords the mono-COT chloro-bridged dimers [M(eta-COT{(SiPr3)-Pr-i-1,4}(2))(mu-Cl)Cl](2), M = Zr (1); M = Hf (4). Further reaction of the latter with 2 equivalents of KCp* yields the crystallographically characterised M(IV) mixed-sandwich complexes [M(eta-COT{(SiPr3)-Pr-i-1,4}(2))(eta-Cp*)Cl], M = Zr (2); M = Hf (5). Reduction of 2 with KC8 in toluene affords the monomeric Zr(III) mixed-sandwich complex [Zr(eta-COT{(SiPr3)-Pr-i-1,4}(2))(eta-Cp*)], whereas the analogous reaction with 5 results in coupling of the COT rings to give dimeric [Hf(eta-Cp*)](2)(mu-eta(7), eta(7)-(C8H6{(SiPr3)-Pr-i-3,6}(2)C8H6{(SiPr3)-Pr-i-3,6}(2))); both 2 and 5 have been structurally characterised.