Reactivity and Structural Effects of Subtle Changes to Cyclopentadienyl Ligands in Actinide Metallocenes

This dissertation focuses on evaluating the effects of changing a single methyl substituent in the well established (C5Me5) 1- ligand system that has dominated actinide organometallic chemistry for decades. Specifically, the substitution with SiMe3 to give (C5Me4SiMe3)1- and with H to give (C5Me4H)1- has led to new classes of actinide complexes as well as new reactivity patterns for actinide-element bonds.;In Chapter 1, the synthesis of the first uranium complexes with the (C 5Me4SiMe3)1- ligand are described. Evaluating the thermal stability of the dialkyl metallocene (C5Me 4SiMe3)2UMe2 led to two C-H bond activations that metalate the SiMe3 groups of both (C5Me 4SiMe3)1- ligands. This yields (C 5Me4SiMe2CH2-kappaC) 2U, a dialkyl complex that has the U-C bonds tethered to a cyclopentadienyl ring through a silylalkyl group. The structural parameters of (C5Me 4SiMe2CH2-kappaC)2U show this to be a viable tethered analog of other uranium dialkyl metallocene complexes.;The complex (C5Me4SiMe2CH2- kappaC)2U provided a unique opportunity to explore U-C bond reactivity in a tethered system, Chapter 2. The tethered U-C bonds were found to be reactive toward insertion substrates such as CO, CO 2, and nitriles. In each case, uranium complexes with new classes of tethered ligands, including enolate, carboxylate, and ketimide, respectively, were produced.;In Chapter 3, unprecedented U-C insertion reactions found with (C5Me4SiMe2CH2-kappaC )2U are described. In the first example of U-C bond reactivity with elemental sulfur, insertion of two S atoms into each U-C bond forms the bis(tethered disulfide) complex (eta5:eta 2-C5Me4SiMe2CH2S 2)2U. In contrast to other uranium dialkyl reactions, C≡N tBu undergoes 1,1-insertion into both U-C bonds to form the first bis(iminoacyl) actinide complex [eta5:eta 2-C5Me4SiMe2CH2C(=N tBu)]2U. This complex undergoes a new mode of isomerization for bis(iminoacyl) metal complexes.;Chapter 4 describes the formation of mixed tether uranium complexes formed from the reactivity of (C5Me4SiMe2CH 2-kappaC)2U with one equivalent of bulky substrate to make (C5Me4SiMe2CH2- kappaC)U(C5Me4SiMe2CH2-substrate) species. This yields complexes with a reactive tethered alkyl (C5Me 4SiMe2CH2-kappaC)2- ligand in the presence of a chelating ligand in the metallocene wedge. The effects of these environments on U-C chemistry was investigated and led to a multi-step cascade reaction that formally involved U-C and C-N bond cleavage, U-O, C-C, and C-N bond formations, and alkyl or silyl migration initiated by CO insertion into a U-C bond.;A description of the use of the (C5Me4SiMe 3)1- ligand to expand an unusual class of sterically crowded tris(polyalkylcyclopentadienyl) complexes is presented in Chapter 5. This resulted in the most sterically congested f element metallocene isolated complex to date, (C5Me4SiMe3)3U, based on the structural parameters and the reactivity observed.;Chapter 6 describes the reactivity of a series of tris(polyalkylcyclopenadienyl) complexes with NO, which led to the isolation of the first f element nitrosyl complex (C5Me4H)3UNO. The structure of (C 5Me4H)3UNO unexpectedly contained a linear U-N-O linkage of the type found for NO1+ metal complexes. However, magnetic susceptibility, spectroscopy, and DFT studies suggest that (C 5Me4H)3UNO contains U4+ and NO 1-.;Studies of the (C5Me4SiMe3)1- and (C5Me4H)1- ligands were also carried out in the area of actinide hydride chemistry, Chapter 7. Although the known (C5Me5)1- based uranium and thorium hydrides, [(C5Me5)2UH 2]2 and [(C5Me5)2ThH 2]2, form from hydrogenation of dimethyl precursors, (C 5Me5)2AnMe2, it was found that hydrogenation of (C5Me4H)2ThMe2 produced a much more complicated multimetallic polyhydride complex, the tetrathorium octahydride (eta5-C5Me4H)4(mu-eta 5:eta1C5Me3CH2H) 2Th4(mu2-H)4(mu3-H) 4.