Chiral actinide complexes

Lin and Marks have considered olefin insertion into the actinide-hydrogen bonds of Cp2An(H)(OR) complexes [Cp = ti -(CH3)5C5 An = Th, U R = achiral or chiral group].Calculations included molecular mechanics analysis of the interaction of Cp U(H) [l(S)-entfo]-bornoxide with norbor-nene. The DREIDING and MMP2 force fields were used to calculate the relative energetics of olefin approach trajectories toward the U center. Three reaction pathways were considered. The authors note that whereas this method is approximate, the energetically favored pathway corresponds to the stereo-chemically favored course of the reaction. 

A very thorough study of insertions of alkenes into the M—H bonds in [( -Cp )2M(H)OR] (M = Th or U R = achiral or chiral alkyl groups temperatures = 30-90 °C), has been reported. In these relatively electron-poor actinide systems, c-olefine complexes are not stable and the insertion products are stable by ca 30kcalmol Reactions are first order in [complex] and [alkene] and the rates with cyclohexene show relatively little dependence on solvent (THF versus toluene) or metal (Th versus U). They do depend on R [fc (t-Bu)/A (CH(t-Bu)2) 10 ]. Activation parameters for reaction of cyclohexene with M = Th, R = r-Bu show a low kH (9kcalmol ) and an exceptionally low AS (—47 cal mol ). Coupled with a modest... 

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