Actinide Metallocene Hydride Chemistry: C H Activation in Tetramethylcyclopentadienyl Ligands to Form μ-η5-C5-C5Me3H(CH2)-κC]2- Tuck-over Ligands in a Tetrathorium Octahydride Complex

Hydrogenolysis of the dimethyl actinide metallocenes (C5Me4SiMe3)(2)UMe2 and (C5Me4H)(2)AnMe(2) (An = Th, U) was examined for comparison with the hydrogenolysis of (C5Mes)2AnMe2 that forms the hydrides 1(C5Me5)(2)ThH2](2), [(C5Me5)(2)UH2](2), and [(CsMe5)(2)UHL. Parallel reactivity is not found with the (C5Me4SiMe3)- and (C5Me4H)complexes. Instead, this study led to the first example of a tuck-over [p-175-05Me(3)H(CH2)-icC](2)- dianion derived from (C5Me4H)- ligands by C H bond activation and rare examples of a polymetallic thorium polyhydride compound and an organometallic Th3+ complex. (C5Me4SiMe3)(2)UMe2 reacts with H-2 to form the bis(tethered alkyl) complex (eta(5)-C5Me4SiMe2CH2-KC)(2)U, a product of C H bond activation of the silyl-methyl groups. The only identifiable product of hydrogenolysis of (C5Me4H)(2)UMe2 is (C5Me4H)(3)U. The first thorium complex of (C5Me4I-)(-) was synthesized by reaction of 2 equiv of (C5Me4H)MgCl(THF) with ThBr4(THF)4 to produce (C5Me4H)(2)ThBr2. This complex reacts with MeLi to make (C5Me4H)(2)ThMe2. The latter complex reacts with H-2 to form the ligand redistribution product (C5Me4H)(3)ThMe and the tetrametallic octahydride tuck-over complex (C5Me4H)(4)D4475-CsMe3H(CH2)-KCbTh4(y-H)(4)(p(3)-H)(4). For comparison with the (C5Me4H)(3)U product, the thorium analogue, (C5Me4H)(3)Th, was synthesized by potassium reduction of a [(C5Me4H)(3)Th][BPh4] intermediate obtained in situ from (C5Me4H)(3)ThMe and [HNEt3] [BPh4]. (C5Me4H)(3)Th can also be prepared from KC8 and (C5Me4H)(3)ThBr, obtained from KC5Me4H and ThBr4(THF)(4).