Uncovering alternate reaction pathways to access uranium(IV) mixed-ligand aryloxide–chloride and alkoxide–chloride metallocene complexes: Synthesis and molecular structures of (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) and (C5Me5)2U(O–tBu)(Cl)

Reaction of the trivalent uranium complex (C5Me5)2U(O-2,6-iPr2C6H3)(THF) (1) with copper(I) chloride affords the corresponding tetravalent mixed-ligand aryloxide–chloride complex (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) (2). The oxidative functionalization protocol cannot be extended to the synthesis of (C5Me5)2U(O–tBu)(Cl) (3) since the corresponding trivalent precursor is not stable. Salt metathesis between (C5Me5)2UCl2 and KOtBu is the method of choice for the preparation of the tetravalent alkoxide–chloride derivative (C5Me5)2U(O–tBu)(Cl) (3). The X-ray crystal structures of (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) (2) and (C5Me5)2U(O–tBu)(Cl) (3) are reported and represent the first structurally characterized uranium(IV) metallocene aryloxide–chloride and alkoxide–chloride complexes, respectively. Both complexes adopt a pseudo-tetrahedral geometry, with a chloride and aryloxide/alkoxide ligand occupying the plane bisecting the metallocene unit.

Graphical abstractReaction of the trivalent uranium complex (C5Me5)2U(O-2,6-iPr2C6H3)(THF) (1) with copper(I) chloride affords the corresponding tetravalent mixed-ligand aryloxide–chloride complex (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) (2). The oxidative functionalization protocol cannot be extended to the synthesis of (C5Me5)2U(O–tBu)(Cl) (3) since the corresponding trivalent precursor is not stable. Salt metathesis between (C5Me5)2UCl2 and KOtBu is the method of choice for the preparation of the tetravalent alkoxide–chloride derivative (C5Me5)2U(O–tBu)(Cl) (3).Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Oxidative functionalization used to prepare U(IV) aryloxide–chloride complexes. ► Salt metathesis is method of choice for the synthesis of U(IV) alkoxide–chloride derivative. ► Oxidation using CuCl limited by stability of precursor trivalent uranium complex. ► First structurally characterized U(IV) metallocene aryloxide– and alkoxide–chloride complexes.