Facile triphenylborane-based syntheses of the sterically crowded tris(pentamethylcyclopentadienyl) complexes (C5Me5)3UMe and(C5Me5)(3)UCl

An atom- and time-efficient synthetic route to sterically crowded organoactinide (C5Me5)(3)-UX complexes involving the in situ formation of borate salts is reported. Addition of BPh3 to (C5Me5)(2)UMeCl followed by KC5Me5 provides a much improved synthesis of (C5Me5)(3)UCl that presumably proceeds through a [(C5Me5)(2)UCl] [MeBPh3] intermediate borate salt. Attempts to make (C5Me5)(3)UMe, the first tris(pentamethylcyclopentadienyl) metal alkyl complex, by reaction of BPh3 with (C5Me5)(2)UMe2 followed by KC5Me5 were also successful, and the product was characterized by X-ray crystallography. In this reaction system, the formation of the borate intermediate, [(C5Me5)(2)UMe] [MeBPh3], was confirmed by variable-temperature NMR spectroscopy and by X-ray crystallography of the THF adduct.