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Chapter 1. The relevant background to the project is communicated in addition to the project hypothesis and strategy. Tetrylene-f-element bonded complexes are introduced as compounds of nearly unexplored chemical reactivity and bonding character. The strategy of combining tetrylenes with coordinatively unsaturated f-element precursors is briefly described.Chapter 2. Novel uranium-tetrylene bonded complexes are synthesized by utilization of amidinate-supported silylenes. The solid- and solution-state structures of these compounds are examined by X-ray crystallography, absorption spectroscopy, nuclear magnetic resonance spectroscopy, and variable-temperature magnetometry. The nature of the uranium-silicon interactions is further elucidated by density functional theory methods.Chapter 3. The reactivity of f-element-silylene complexes toward hydrogen gas is reported. Despite showing little evidence for bonding in solution, a uranium-silylene complex rapidly activates hydrogen to yield a dihydrosilane product. Lanthanide analogues to the uranium-silylene complex are much less efficient catalysts, while common main group Lewis acids show no catalytic activity. The mechanisms of both the actinide- and lanthanide-catalyzed reactions are deconvoluted through isotope labeling studies and kinetic and theoretical modeling. Investigation of the uranium-catalyzed pathway reveals that dihydrogen complexation by uranium is accessible and may underpin the particular efficiency of this catalyst.

This dissertation describes efforts to expand the understanding of Ln(II) chemistry, particularly that of the non-traditional 4fn5d1 ions, through the synthesis and isolation of new Ln(II) species supported by bis(trimethylsilyl)amide ligands and exploration of their reactivity. Described herein is the isolation of a new series of Ln(II) complexes ligated by NR2 (R = SiMe3) ligands. These ligands were previously not thought to be capable of supporting the nontraditional lanthanide ions in the 2+ oxidation state. Following their isolation, the reaction chemistry of these [LnIINR2)3]1− complexes was investigated to provide insight into the unique reaction chemistry of non-traditional Ln(II) ions. Chapter 1 outlines the synthesis and characterization of a new series of Ln(II) complexes [M(crypt)][Ln(NR2)3] (M = K or Rb) and describes their spectroscopic properties as they relate to electron configuration. Chapter 2 discusses the synthesis of the elusive [YII(NR2)3]1− complex in addition to reactions of [Ln(NR2)3]1− with CO. Chapter 3 describes new examples of uranium in the +2 oxidation state isolated by reduction of Cptet3U (Cptet = C5Me4H) and U(NR2)3 (R = SiMe3) in the presence of 2.2.2-cryptand to produce [K(crypt)][Cptet3U] and [K(crypt)][U(NR2)3], respectively. Chapter 4 expands the understanding of lanthanide-based dinitrogen reduction chemistry through discovery of the first end-on Ln2(μ-η1:η1-N2) complexes. The formation of end-on versus the more common side-on Ln2(μ-η2:η2-N2) complexes was possible by using the Ln(II) complexes detailed in Chapters 1 and 2. Chapter 5 details the reaction chemistry of the [Gd(NR2)3]1− complexes with toluene and the isolation of a methylcyclohexadienyl dianion. Chapter 6 discusses the reaction chemistry of [Gd(NR2)3]1− with BiPh3 and PPh3 and the formation of a rare example of a complex containing a Ln−Bi bond.

This dissertation describes the targeted attempts at the generation of transition metal species that function as precise electronic structure mimics to the well known spin triplet (S =1) metal carbonyls fragments Fe(CO)4 and CpCo(CO). These unsaturated fragments have been shown to display a wide range reactivity, and competency towards important reaction chemistry such as alkane and N2 binding, and E–H bond activation due to a unique interplay of a strong ligand field, formal dn count, and orbital symmetry, rendering these fragments primed for bond activation. Accordingly, ligand architectures that can accurately mimic the ligand field provided by CO to kinetically stabilize these fragments could provide new inroads to novel small molecule activation pathways. To this end, sterically encumbering m-terphenyl isocyanides serve as isolobal ligand surrogates for carbon monoxide (CO). Additionally isocyanides have the added benefit of providing kinetic stabilization by virtue of readily tunable isocyano–R (CN–R) group. The first section of this dissertation describes the synthesis and protonation of an encumbered tetra-isocyanide iron dianion, Na2[Fe(CNArMes2)4] (ArMes2 = 2,6-(2,4,6 –Me3C6H2)2C6H3), which serves as a platform for targeting species of the formulation Fe(CNArMes2)4. It is shown that the reactivity of the electronically unsaturated Fe(CNR)4 fragment upon protonation of Na2[Fe(CNArMes2)4] and subsequent alkylation of Na[HFe(CNArMes2)4], yields the dinitrogen stabilized species Fe(N2)(CNArMes2)4. Fe(N2)(CNArMes2)4 is shown to readily undergo intramolecular C–H activation of the ligand scaffold upon liberation N2 under ambient conditions purportedly through and insipient [Fe(CNArMes2)4] fragment. Further more, ability of Na2[Fe(CNArMes2)4] to facilitate the reductive disproportionation of CO2, in addition to CO2 capture with electrophilic silyl sources is presented culminating in a rare class of low valent Fe-aminocarbyne complexes. The second vignette of this dissertation focuses on the generation of species that mimic the formulation CpCo(L). It is shown that with less encumbering m-terphenyl isocyanides that aggregation akin to the unsaturated carbonyl congeners is realized. Use of encumbering m-terphenyl isocyanides provides access to the three memebered electron transfer series [(µ2-CNArMes2)2[CpCo]2]n (n = 0,–1, –2). Notably, this series is the first of its kind to span all three ostensible electronic states (e.g. d8-d8, d8-d9, and d9-d9), previously unavailable with other π-acidic ligand frameworks. Additionally this allows for a systematic reassessment of the metal-metal bonding within this class of dimeric species. Evidence is put forth in favor of no M–M bonding interactions occur within these systems and the integrity of the dimeric framework is in fact mitigated through a unique interplay of the metal d-manifold and the isocyanide π*–system. Modulation of the steric profile of the m-terphenyl isocyanide and the Cp unit to Cp* so as to increase the steric pressure provides access to the first reported mono-nuclear Cp*Co(N2)L fragments. It is shown that these species function as viable sources of Cp*Co(CNR) for a number of bond activation processes including Si–H, H–H, and P–P bond scission. Moreover, the reactivity of these species culminates with the isolation of the second example of a structurally authenticated transition metal nitrous oxide (N2O) adduct, which exhibits an unprecedented η2–(N,N) coordination mode to Co. Finally, the reduction of the encumbered Cp*Co(CNArTripp2) (CNArTripp2 2,6-(2,4,6-(i-Pr)3C6H3)2C6H3) fragment provide access to the unique dianion K2[Cp*Co≡CNArTripp2]. It is shown that the dianion K2[Cp*Co≡CNArTripp2] exhibits 3-fold bonding between Co and the isocyanide –Ciso through an extreme case of M→(CN) π*-back donation and gives rise to the first example of a Co-carbyne complex. The reactivity and electronic structure are presented for K2[Cp*Co≡CNArTripp2] and it is concluded that this reactive dianion behaves as a potent metal based nucleophile and source of [Cp*Co(CNR)]2– for a number of bond activation process.

The mechanism for the addition of alkynes to low-valent silicon compounds was investigated in this thesis using a cyclopropyl alkyne mechanistic probe (1.31). The addition of alkyne 1.31 to the asymmetrically-substituted disilene 1.37 was investigated. The structures of the products obtained indicate the reaction proceeds through a stepwise mechanism with a biradical intermediate and the dipole moment of the disilene bond was not sufficient to alter the reaction mechanism. The addition of alkyne 1.31 to the NHC-stabilized silylene 1.38 was also investigated. The structure of the product formed in the reaction lead to two conclusions: that silylene 1.38 acts as a nucleophile in the reaction with alkyne 1.31, and the cyclopropyl ring of alkyne 1.31 regioselectively opens toward the phenyl substituent in the presence of an α-anion.

In this thesis, the synthesis, characterization and applications of aluminum compounds and cluster from aluminum monohalide solutions, AlX (where X = Cl or Br) are described. Chemistry of AlX solutions is not well understood, but AlX has proven adept at producing aluminum metalloid clusters (AlnLm where n>m). A brief overview of the renaissance of low-valent aluminum chemistry and select low-valent Al products is presented as background. The neutral mononuclear aluminum tris-bpy complexes [Al(Mebpy)3] and [Al(tBubpy)3] have been synthesized, isolated, and structurally characterized via X-ray single crystal diffraction. These complexes are the first structurally characterized homoleptic tris-bpy complexes and were studied via ESI-MS, d.c. magnetic susceptibility, electrochemical analyses. Electrochemistry demonstrates that six oxidation states are accessible from both neutral complexes: [Al(Rbpy)]n (n = -3 to 3, R = Me or tBu). The [Al(Mebpy)3] complex demonstrates unexpected magnetic ordering at 19 K which is not observed in [Al(tBubpy)3] nor in transition metal centered tris-bpy congeners. Synthesis, isolation, and characterization of the low-valent aluminum cluster [LiOEt2]2[HAl3(PPh2)6] via NMR and ESI-MS studies are also described. These experiments proved the presence of an H atom, and developed a complete and comprehensive picture of the structure, magnetism, and spectroscopy of this compound. Solution studies of reactions of AlBr with tBu-thiolate via ESI-MS show the formation and identification of [Al17Br(StBu)10S3]1-, [Al10(StBu)4S5]1-, [Al13(StBu)4BrS]1-, and [Al5(StBu)7Br]1-¬ in solution. The preparation and characterization of the aluminum (III) thiolate complex, Na[Al(SPh)4], is also described. These studies demonstrate the importance of reaction conditions in the formation of aluminum clusters in solution, and the viability of thiolate ligands to isolate low-valent aluminum products. Al nanoparticles (NP) can be produced from AlX solutions and have been successfully supported on both graphene and graphene oxide. The reduction of AlX solutions are quick, facile, and performed at low temperatures (-78°C). In the presence of graphene, faceted and well-dispersed graphene supported Al-NPs can be obtained. The [AlBrNEt3]4 cluster is isolated from AlBr⋅NEt3 solution and is soluble in toluene and diethyl ether. The burning rate of the hydrocarbon fuel doped with the tetramer is studied. There is an increase in burning rate attributed to the presence of [AlBrNEt3]4.