Sterically encumbered mixed sandwich compounds of uranium(III): synthesis and reactivity with small molecules

A series of uranium(III) mixed sandwich complexes with sterically demanding CpR ligands, of the type [U(COTTIPS2)(CpR)] (CpR = CptBu (C5H4tBu), CptBu2 (C5H3tBu2-1,3), CptBu3 (C5H2tBu3-1,2,4), CpTIPS2 (C5H3(SiiPr3)2-1,3), CpMe4Bz (C5Me4CH2Ph), IndMe6 (C9HMe6) and IndMe7 (C9Me7), and COTTIPS2 = C8H6(SiiPr3)2-1,4), have been synthesised and their X-ray crystal structures determined. The reactivity of these complexes with CO and CO2 is reported, including the squarate complex [U(COTTIPS2)(IndMe6)]2(µ-C4O4), IR data on the long-lived carbonyl complex [U(COTTIPS2)(IndMe7)(CO)] and the carbonate complex [U(COTTIPS2)(CptBu)]2(µ-?1:?2-CO3). The Solid-G algorithm has been to assess the steric properties of these and previously reported mixed-sandwich complexes in the solid state and correlate these properties with the observed reactivity.