Facile Triphenylborane-Based Syntheses of the Sterically Crowded Tris(pentamethylcyclopentadienyl) Complexes (C5Me5)3UMe and (C5Me5)3UCl

An atom- and time-efficient synthetic route to sterically crowded organoactinide (C 5 Me 5 ) 3 UX complexes involving the in situ formation of borate salts is reported. Addition of BPh 3 to (C 5 Me 5 ) 2 UMeCl followed by KC 5 Me 5 provides a much improved synthesis of (C 5 Me 5 ) 3 UCl that presumably proceeds through a [(C 5 Me 5 ) 2 UCl][MeBPh 3 ] intermediate borate salt. Attempts to make (C 5 Me 5 ) 3 UMe, the first tris(pentamethylcyclopentadienyl) metal alkyl complex, by reaction of BPh 3 with (C 5 Me 5 ) 2 UMe 2 followed by KC 5 Me 5 were also successful, and the product was characterized by X-ray crystallography. In this reaction system, the formation of the borate intermediate, [(C 5 Me 5 ) 2 UMe][MeBPh 3 ], was confirmed by variable-temperature NMR spectroscopy and by X-ray crystallography of the THF adduct.