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

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-?1:?2-CO3) and {Th(COTTIPS2)Cp*}2(µ-?2:?2-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-?1:?1-O2CH)}2.