This thesis first reports on several features of intramolecular, and in one case intermolecular, C--H bond activation reactions which occur at thorium centers. The studies of intramolecular C--H bond activation include the syntheses, structures and cyclometalation reactions of a series of bis(pentamethylcyclopentadienyl)thorium dialkyl complexes. The mechanism for cyclometalation is proposed to involve a concerted, heterolytic process with hydrogen atom abstraction and metallacycle formation occurring in a four-center transition state. The equilibrium constant, as well as forward and reverse rate constants for the C--H bond activating equilibrium: Cp'(,2)Th(CH(,2)SiMe(,3))(,2) () Cp'(,2)ThCH(,2)SiMe(,2)CH(,2) + Me(,4)Si (Cp' = (eta)('5) - C(,5)Me(,5)); have been measured and give (DELTA)H('o) = +4.6(3) kcal mol('-1), and (DELTA)S('o) = +16.6(5) eu; (DELTA)H('(DBLDAG))(,fwd) = +22.4(3) kcal mol('-1) and (DELTA)S('(DBLDAG))(,fwd) = -17.6(5) eu; and (DELTA)H('(DBLDAG))(,rev) = +17.8(5) and (DELTA)S('(DBLDAG))(,rev) = -34.2(5) eu. Second, this thesis reports on the synthesis, structures, and dynamic NMR behavior of the methylene bridged heterobimetallic complexes obtained in reactions of Cp'(,2)Th(CH(,2)CMe(,2)CH(,2)) (1), as follows. Treat- ment of 1 with Cp(,2)ZrMe(,2) (Cp = (eta)('5)-C(,5)H(,5)) in saturated hydrocarbon solvents yields Cp'(,2)Th((mu)-CH(,2)) ((mu)-h1:(eta)('5)-C(,5)H(,4))ZrCp(Me) (2) and neo- pentane, while reaction between 1 and Cp(,2)HfMe(,2) gives Cp'(,2)Th((mu)- CH(,2)) ((mu)-h1:(eta)('5)-C(,5)H(,4))HfCp(Me) (3). Reaction of 1 and Cp''(,2)ZrMe(,2) gives Cp'(,2)Th((mu)-CH(,2)) ((mu)-h1:(eta)('5)-3,4-C(,5)Me(,2)H(,2))Zr(Cp'')Me (Cp'' = (eta)('5)-1,2-Me(,2)H(,3)C(,5)) (4). These compounds all exhibit a fluxional process which exchanges diastereotopic hydrogen atoms on the (mu)-methyl- ene with (DELTA)G('(DBLDAG)) (T(,c)) for 2 of 11.2(3) kcal mol('-1) (277 K) in toluene and 11.5(2) kcal mol('-1) (287 K) in THF, for 3 of 11.5(2) kcal mol('-1) (268 K) in toluene, and for 4 of 11.8 (2) kcal mol('-1) (282 K) in toluene. Finally, this thesis describes the synthesis and properties of the actinide s-cis-diene/cis-2-butene-1,4-diyl complexes Cp'(,2)U((eta)('5)-C(,4)H(,6)) (5), Cp'(,2)Th((eta)('4)-C(,4)H(,6)) (6), and Cp'(,2)Th((eta)('4)-CH(,2)C(Me)C(Me)CH(,2)) (7). These complexes may be prepared from Cp'(,2)MCl(,2) and the appropriate (THF)(,2)Mg(CH(,2)C(R)C(R)CH(,2)) reagent in THF.