Synthesis of β- Diketiminate-Supported Yb(II) Complexes: Toward the Hydroarylation of Benzene

The synthesis and reactivity of β-diketiminate-supported ytterbium(II) complexes bearing the sterically demanding DipepBDI ligand are reported as part of efforts to develop lanthanide(II) hydride platforms for the hydroarylation of benzene. Salt metathesis between (DipepBDI)K and YbI2 afforded a solvent-free ytterbium(II) iodide complex that adopts an unusual polymeric solid-state structure. Subsequent metathesis reactions provided the corresponding ytterbium(II) amide and bis(trimethylsilyl)methyl complexes, the latter representing a rare three-coordinate Yb(II) alkyl species and displaying pronounced susceptibility toward ethereal solvent coordination. The target ytterbium(II) hydride was accessed through both hydride transfer from the amide precursor and hydrogenolysis of the alkyl complex, with the latter route enabling clean, scalable synthesis. Exposure of the hydride to ethene generated spectroscopic evidence for a mixed hydride–ethyl intermediate; however, the desired nucleophilic alkylation of benzene was outcompeted by intramolecular C–H activation of a flexible N-Dipep substituent to give an allyl-functionalized ytterbium(II) product. These findings demonstrate that the DipepBDI framework can effectively stabilize highly reactive Yb(II) hydride and alkyl species, but also reveal that ligand flexibility and proximal C–H bonds impose a critical limitation for lanthanide(II)-mediated hydroarylation catalysis.