This contribution reports a kinetic/mechanistic/stereochemical/molecular mechanics study of olefin insertion into the actinide-hydrogen bonds of CP'~A~(H)(OR) complexes (Cp' = V~-( C H~)~C~; An = Th, U; R = achiral or chiral alkyl group). For the reaction Cpf2An(H)(O-t-Bu) + cyclohexene (An = Th), the rate law is first order in organoactinide and first order in olefin, with kWH/kWD = 1.4 ( l ) , kmf/ktolucnc = 0.59 ( 5 ) , AH* = 9.0 ( 5 ) kcal/mol, and A s * = -47.2 (1) eu; kU/kTh = 1.5. For Cp'2Th(H)[OCH(t-Bu)2] + I-hexene, ka-H/kn-D = 1.3 (2). Alkoxide effects on insertion rates can be large, and for Cpf2Th(H)(OR) + cyclohexene, k6f-Bu/koCH(f.h)2 Z IO3. For Cp',Th(H)[OCH(t-Bu),], relative insertion rates follow the ordering ethylene > I-hexene > 4-methoxystyrene > styrene >> cyclohexene; kc-rcn/ka-e = 2.2 ( 5 ) . For cis-2-butene, insertion reactions yield sec-butyl derivatives that slowly rearrange to the n-butyrisomers. Insertion experiments with CpiAn(H)(OR*) complexes having chiral alkoxide ligands (OR* = (IR,2S,SR)-menthoxide; (R)-2-butoxide; [( 1s)endo]-bornoxide; (IS,2S,SR)-neomenthoxide) and prochiral olefins (norbornene, cis-2-butene) or ketones (acetophenone,butyrophenone) demonstrate that maximum diastereoselection occurs for sterically encumbered reagents at low temperatures (de = 36% for norbornene at -45 "C). A molecular mechanics/molecular graphics analysis suggests that the sterically most favorable direction of olefin approach toward the actinide center is between the U-H and U-0 bonds rather than from the side. These results provide additional insight into ancillary ligand effects on the kinetics of organo-f-element-catalyzed olefin hydrogenation.The insertion of olefinic functionahties into metal-hydride bonds is a crucial step in numerous stoichiometric, homogeneous catalytic, and heterogeneous catalytic processes occurring at do transition element and f element centers.'" Mechanistically, such insertion processes are not in general well-understood and are necessarily operative in very different metal-ligand environments than the more extensively studied analogues at middle-and late-transition element centers?.' Thus, the do/f metal ion is likely ( I ) (a) Cardin, D. J.; Lappert, M. F.; Raston, C. L. (7) (a) Burger, B. J.; Santarsiero, B. D.; Trimmer, M. S.; Bercaw, J. E. Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann, H.; Marks, T. J. J. Am. Chem. SOC. 1985,107,8091-8103. (c) Jeske, G.; Schock, L. E.; Swepston. P. J.; Schumann, H.; Marks, T. J. J . Am. Chem. SOC. 1985, 107, 8103-8110. (d) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T. J.