This dissertation describes the synthesis and characterization of a series of copper(I) thiolates and Tin-containing derivatives featuring as attractive London dispersion effects and rare structures with unusual chemical behavior.

Chapter 2 describes the synthesis of the first two-coordinate, dimeric copper thiolato complexes {CuSAr*}2 and comparison of copper thiolates with their lithium congeners. Reactions of the large terphenyl thiols HSAr* (Ar* = very bulky terphenyl ligands) with stoichiometric amounts of mesitylcopper(I) afforded the corresponding two-coordinate, dimeric copper thiolato species {CuSAr*}2. These complexes feature centrosymmetric dimeric structures with planar Cu2S2 core in which the two Cu atoms are bridged by sulfurs from two terphenyl thiolato ligands, which bear a resemblance to the CuA site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. Single X-ray crystallography shows that the Cu derivatives feature much longer Cu- -Cu distances than the Li--Li distances in their dimeric Li congeners. Given the very similar effective ionic radii of the Li+ (0.59 Å) and Cu+ (0.60 Å) ions, this unusual phenomenon is probably a consequence of stronger dispersion interactions which are caused by a higher degree of instantaneous induced dipoles between copper atoms.

Chapter 3 is an extension of the studies in Chapter 2. Further investigation of the reactions described in Chapter 2 revealed that the adjustment of the amount of mesitylcopper(I) afforded a new type of heteroleptic aryl Cu(I) thiolato compounds with formula {Cu2(SAr*)Mes}2 (Ar* = very bulky terphenyl ligands). The molecular structures of those compounds show they all display tetrametallic Cu4 cores in which two thiolato or two mesityl ligands bridge the metals. It is noteworthy that the use of relatively less bulky thiolato ligands yielded products that feature the expected conventional alternating thiolato and mesityl bridging patterns. Nevertheless, switching to bulkier ligands afforded a previously unknown structural arrangement in which the two thiolato ligands are adjacent to each other. The new complex with cis arrangement of the ligands is sterically counterintuitive which is likely due to London dispersion (LD) energy effects. Dispersion corrected DFT calculations have been carried out to show that 3 has the highest LD effect stabilization arising from the increased numbers of C-H···H-C interactions of the isopropyl ligand substituents.

Chapter 4 depicts the London dispersion effects in an equilibrium of distannene and a tristannane with identical substituents. {Sn(C6H2-2,4,6-Cyp3)2}3, a new cyclotrisyannane, was produced by reacting lithium salt {LiC6H2-2,4,6-Cyp3·Et2O}2 with SnCl2 in Et2O at -78oC. Variable temperature (VT) 119Sn NMR spectroscopy shows {Sn(C6H2-2,4,6-Cyp3)2}3 can be converted to the distannene {Sn(C6H2-2,4,6-Cyp3)2}2 upon heating in hydrocarbon solution. However, the presence of the corresponding monomer :Sn(C6H2-2,4,6-Cyp3)2 at elevated temperature was not detected neither by VT 119Sn NMR spectroscopy nor by 1H-DOSY NMR spectroscopy. The suppression of the formation of the monomeric stannylene is a reflection of enhanced London dispersion energy between the two Sn(C6H2-2,4,6-Cy3)2 units in the {Sn(C6H2-2,4,6-Cyp3)2}3 and {Sn(C6H2-2,4,6- Cyp3)2}2, as evidenced by multiple computational studies. Van’t Hoff analysis revealed a cyctristannane {Sn(C6H2-2,4,6-Cyp3)2}3 to distannene {Sn(C6H2-2,4,6-Cyp3)2}2 conversion ΔHconv. energy value of 33.36 kcal mol−1 and a ΔSconv. value of 0.102 kcal mol−1 K-1, which gives ΔGconv.300 K = 2.86 kcal mol−1.

Chapter 5 described novel reactivities of stannylene :Sn(C6H3-2,6-(C6H3-2,6-iPr2)2)2 with phenylacetyene and diphenylacetylene. Stannylenes have shown high reactivities towards unsaturated small molecules (CO, alkene, alkyne, azide, etc...) due to their relatively modest HOMO-LUMO gap. However, only a few reactions of stannylene (:SnR2) with alkynes have been investigated so far. This chapter depicts the reactions of diaryl stannylene Sn(C6H3-2,6-(C6H3-2,6- iPr2)2)2 with terminal or non-terminal alkynes in benzene at elevated temperature, from which aryl alkyl stannylene products were isolated and characterized by X-ray crystallography and spectroscopy.

Abstract. A series of studies of the chemistry of first-row transition metal M{N(SiMe3)2}3 complexes is described herein. Both divalent M{N(SiMe3)2}2 and trivalent M{N(SiMe3)2}3 transition metal complexes have been described in the literature since the early 1960s. However, while the divalent complexes have been the subject of a great deal of study, comparatively little attention has been paid to the trivalent complexes since their initial discovery. The reason for this disparity appears to be the notion that the steric crowding in these molecules results in their low reactivity. Although work in this laboratory has periodically examined these complexes, our most recent interest stemmed from the observation that the detailed molecular structure of the vanadium complex V{N(SiMe3)2}3 had been absent from the literature as recently as 2019, despite the complex having been reported in 1971. By isolating this complex as violet-colored crystals, Wagner and coworkers determined that the original report of ‘brown’ V{N(SiMe3)2}3 had probably mischaracterized this material. This observation encouraged us to reexamine the chemistry of these classic metal amido complexes, which revealed a vibrant chemistry that had not been described until now.

Chapter 2 describes the synthesis and characterization of a series of M{N(SiMe3)2}3L2 complexes (L = nitrile or isocyanide ligand) of titanium and vanadium. Although it had been initially thought that the considerable steric crowding in M{N(SiMe3)2}3 complexes precluded the formation of Lewis base complexes, it is shown that the formation of such donor complexes is possible by judicious selection of the donor molecule (isocyanide or nitrile bases). A spectroscopic study of these complexes revealed that the donors are only weakly bound in solution, with stronger binding in the case of the vanadium complexes. Furthermore, we observed no complex formation for M = Cr, Mn, Fe, or Co, a property that we attribute to the absence of empty, low-energy orbitals available in the later metals to accept electrons from donor molecules.

In Chapter 3, we exploit the observations made in Chapter 2 to show that V{N(SiMe3)2}3 can be oxidized by reagents similar in shape to the Lewis bases used to form M{N(SiMe3)2}3L2 complexes. Thus, the reaction of V{N(SiMe3)2}3 with iodosylbenzene (PhIO) or trimethylsilylazide (Me3SiN3) afforded the vanadium(V) complexes V(=O){N(SiMe3)2}3 or V(=NSiMe¬3){N(SiMe¬3)2}3, respectively, which were studied structurally and spectroscopically. Despite several reports of its attempted synthesis, V(=O){N(SiMe3)2}3 had not been isolated until now. It had been suggested that the V=O moiety reacts with a ligand trimethylsilyl group to give the V(OSiMe3)(=NSiMe3){N(SiMe3)2}2 ¬isomer. Indeed, we show this to be the case, and provide a kinetic study of this transformation in solution.

Chapter 4 describes the reduction of M{N(SiMe3)2}3 (M = V, Cr, Fe) complexes with the metal hydride reagents LiAlH4 or AlH3(NMe3). Thus, the reaction of V{N(SiMe3)2}3 with LiAlH4 afforded the highly unstable polyhydride [V(µ2-H)6[Al{N(SiMe3)2}2]3][Li(OEt2)3]. In contrast, the reaction of V{N(SiMe3)2}3 with LiAlH4 in the presence of 12-crown-4 gave the rare terminal hydride [VH{N(SiMe3)2}3][Li(12-crown-4)2]. The presence of this hydride was verified by the preparation and spectroscopic study of the corresponding deuteride complex [VD{N(SiMe3)2}3][Li(12-crown-4)2] by the reaction of V{N(SiMe3)2}3 with LiAlD4 in the presence of 12-crown-4. The reaction of LiAlH4 with M{N(SiMe3)2}3 (M = Cr, Fe) in the presence of 12-crown-4 afforded the ionic metal(II) complexes [M{N(SiMe3)2}3][Li(12-crown-4)2], rather than any hydride complexes. In the absence of 12-crown-4, the reaction of Fe{N(SiMe3)2}3 with LiAlH4 gave the so-called “hydrido inverse crown” complex [Fe(µ2-H){N(SiMe3)2}2(µ2-Li)]2, while treatment of the same trisamide with AlH3·NMe3 afforded the mixed-metal polyhydride Fe(µ2-H)6[Al{N(SiMe3)2}2]2[Al{N(SiMe3)2}(NMe3)].

Chapter 5 describes attempts to prepare divalent M{N(SiMe3)2}2 complexes of titanium and vanadium by reduction of the corresponding M(Cl){N(SiMe3)2}2 complexes. Additionally, efforts to determine the fate and role of the bromine atom in the synthesis of M{N(SiMe3)2}3 (M = Mn, Co) complexes by oxidation of the divalent M{N(SiMe3)2}2 with BrN(SiMe3)2 are detailed. Reduction of Ti(Cl){N(SiMe3)2}2 with 5 %(wt) sodium on sodium chloride afforded the unusual mixed-metal, mixed-valent Ti(III/IV) hydride complex Ti2(μ-H)2{N(SiMe3)2}3{N(SiMe3)(SiMe2CH)}(Na) rather than “Ti{N(SiMe3)2}2,” while the analogous reaction using V(Cl){N(SiMe3)2}2 gave only a mixture of intractable products. After isolation of Co{N(SiMe3)2}3 formed by the reaction of BrN(SiMe¬3)2 with Co{N(SiMe3)2}2, storage of the mother liquor afforded a small amount of crystalline, polymeric [(μ-Br)Co{μ-N(SiMe3)(SiMe2CH2CH2Me2Si)(Me3Si)μ-N}Co(μ-Br)]ꝏ, indicating that the three products of this reaction are Co{N(SiMe3)2}3, HN(SiMe3)2, and the aforementioned polymer. In order to better understand the role of bromine in these oxidations, we also treated M{N(SiMe3)2}2 (M = Mn or Co) with elemental bromine. Surprisingly, treatment of Mn{N(SiMe3)2}2 with bromine gave the trisamide Mn{N(SiMe¬3)2}3 as the only isolated product. In contrast, the reaction of Co{N(SiMe¬3¬)2}2 with elemental bromine gave the heteroleptic [Co(Br){μ-N(SiMe3)2}]2.

Chapters 6 and 7 differ from the preceding chapters in that the focus is no longer the chemistry of transition metal amide complexes. In Chapter 6, the synthesis and characterization of several homoleptic, dimeric aryloxide and thiolate complexes of iron are described. Thus, treatment of [Fe{N(SiMe¬3)2]2¬ with the appropriate phenol or thiol affords the dimers {Fe(OC6H2-2,6-But2-4-Me)2}2 and {Fe(OC6H3-2,6-But2)2}2, or the monomeric Fe{SC6H3-2,6-(C6H3-2,6-Pri2)2}2. Recrystallization of {Fe(OC6H2-2,6-But2-4-Me)2}2 or {Fe(OC6H3-2,6-But2)2}2 from diethyl ether gives the corresponding three-coordinate ether complexes Fe(OC6H3-2,6-But2-4-Me)2(OEt2) and Fe(OC6H3-2,6-But2)2(OEt2). However, recrystallization of the thiolate Fe{SC6H3-2,6-(C6H3-2,6-Pri2)2}2 from diethyl ether afforded no new products. Fe(OC6H3-2,6-But2-4-Me)2(OEt2) and Fe(OC6H3-2,6-But2)2(OEt2) were found to weakly coordinate ether in solution, a property which allowed the complete assignment of the 1H NMR spectra of the parent dimers and the monomeric diethyl ether complexes. In contrast to the weak coordination of diethyl ether, the iron aryloxides were shown to strongly complex ammonia as exemplified by the four-coordinate Fe(OC6H2-2,6-But2-4-Me)2(NH3)2, which does not lose diethyl ether in solution or under heating and low pressure. Alternatively, Fe{SC6H3-2,6-(C6H3-2,6-Pri2)2}2 was shown to reversibly bind either one or two ammonia molecules, giving the products Fe{SC6H3-2,6-(2,6-Pri2-C6H3)2}2(NH3) and Fe{SC6H3-2,6-(2,6-Pri2-C6H3)2}2(NH3)2.

In Chapter 7, work on the design of a ‘dispersion effect donor’ ligand which is capable of stabilizing a dimeric R2SnSnR2 species in solution is described. The vast majority of distannene (R2SnSnR2) molecules possess only weak Sn-Sn interactions and thus dissociate into monomeric stannylene (SnR2) fragments in solution. However, we show that the reaction of 2 eq. of LiC6H2-2,4,6-Cy¬3¬·OEt2 (Cy = cyclohexyl) with SnCl2 afforded the distannene {Sn(C6H2-2,4,6-Cy3)2}2, which remains a dimer in solution even at elevated temperatures. A computational study revealed that the origin of its stability is the London dispersion attraction between multiple close contacts of ligand C-H moieties across the Sn-Sn bond. Whereas the only previous example of a distannene to remain a dimer in solution at ambient temperature was shown to be stabilized by strong covalent interactions between tin atoms, we show here that Sn-Sn interactions in {Sn(C6H2-2,4,6-Cy3)2}2 are comparatively weak, and that its stability is mainly due to London dispersion effects.

This dissertation describes the reactivity of a terphenyl-substituted heavier group 14 dimetallyne, and a diplumbyne with dinuclear transition metal carbonyls, as well as the synthesis and reactivity of certain divalent tin hydrides. The solid-state structures of the reaction products of these preparations are determined by single X-ray crystallography. Other characterization methods include nuclear magnetic resonance spectroscopy, UV-visible spectroscopy, infrared spectroscopy. A summary of the previous investigations of the synthesis and reactivity of heavy group 14 dimetallynes and the prior studies on the synthesis and reactivity of divalent tin hydrides are described in Chapter 1. Chapter 2: In this chapter, it is shown that the metathesis reactions of the diplumbyne AriPr6Pb≡PbAriPr6 (AriPr6 = −C6H3–2,6-(C6H2–2,4,6-iPr3)2) with the dinuclear metal carbonyls Mn2(CO)10, Fe2(CO)9, and Co2(CO)8 under mild conditions afford the complexes Mn(CO)5(PbAriPr6) (1), Fe(CO)4(PbAriPr6)2 (2), and Co4(CO)9(PbAriPr6)2 (3), respectively. Complexes 1–3 are structurally characterized by single-crystal X-ray diffraction and spectroscopically characterized by 1H, 13C{1H}, 59Co{1H}, and 207Pb{1H} NMR; UV–vis; and IR methods. They are rare examples of species formed by the direct reaction of a group 14 dimetallyne with transition metal carbonyls. Complexes 1 and 2 feature Mn–Pb or Fe–Pb single bonds, whereas in 3 a Co–Pb cluster is formed in which the plumbylidyne moiety bridges either an edge or a face of a Co4 carbonyl cluster. Chapter 3: In this chapter, it is shown that the reaction of the aryltin(II) hydrides {AriPr4Sn(μ-H)}2 or {AriPr6Sn(μ-H)}2 (AriPr4 = –C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = –C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the molybdenum carbonyl [Mo(CO)5(THF)] yields the divalent tin hydride transition metal complexes, Mo(CO)5{Sn(AriPr6)H}, (1), or Mo(CO)5{Sn(AriPr4)(THF)H} (2), respectively. Complex 1 effects the facile hydrostannylation of carbon dioxide, to yield Mo(CO)5{Sn(AriPr6)(κ2-O,O′-O2CH)}, (3), which features a bidentate formate ligand coordinating to the tin atom. Reaction of 3 with the pinacolborane, HBpin (pin = pinacolato), in benzene regenerates 1 in quantitative yield by NMR spectroscopy. All complexes are characterized by X-ray crystallography, as well as by UV-visible, IR, and multinuclear NMR spectroscopies. The isolation of 1 and 2 is consistent with the existence of monomeric forms of {AriPr4Sn(μ-H)}2 and {AriPr6Sn(μ-H)}2 in solution. Regeneration of 1 from 3 via reaction with pinacolborane as the hydrogen source shows the catalytic potential of 1 in the hydrogenation of CO2. Chapter 4: In this chapter, it is shown that reaction of the aryltin(II) hydride {AriPr6Sn(µ-H)}2 (AriPr6 = -C6H3-2,6-(C6H2-2,4,6-iPr3)2) with two equivalents of the tungsten carbonyl THF complex, [W(CO)5(THF)], gives the divalent tin hydride transition metal complex, W(CO)5{Sn(AriPr6)H}, (1). Complex 1 reacts rapidly with ethylene, or propylene under ambient conditions to yield the corresponding hydrostannylated organometallic species, W(CO)5{Sn(AriPr6)(Et)} (2), or W(CO)5{Sn(AriPr6)(nPr)} (3), via olefin insertion into the Sn-H bond. Treatment of 1 with the Lewis base dbu (dbu = 1,8-diazabicycloundec-7-ene) yields the Lewis acid-base complex, W(CO)5{Sn(AriPr6)(dbu)H} (4), indicating that the Lewis acidity of the tin atom is preserved in 4. The complexes were characterized by X-ray crystallography, and by UV-visible, FT-IR, and multinuclear NMR spectroscopies. DFT calculations by Dr. Petra Vasko suggest hydrostannylation of ethylene with 1 proceeds via coordination of ethylene to the tin atom, then insertion into the Sn-H bond. Further computational study on the reactivity of 1 towards Ph3SiH indicated that the rate-determining step involves the metathesis reaction of a Sn-C/Si-H bond with a very high energy barrier being 71.3 kcal/mol. The calculated proton abstraction product of 1 with dbu, [W(CO)5{Sn(AriPr6)}]+[H(dbu)]-, is 18.2 kcal/mol less stable than the observed coordination product 4.

The use of sterically demanding m-terphenyl ligands to kinetically stabilize unusual low coordinate molecular geometries in organometallic complexes of aluminum and lead are described. The influence of attractive intramolecular interligand London dispersion forces on their structures was also studied. In Chapter 2, rare examples of diplumbynes, dilead analogues of alkynes, of the formula RPbPbR with lead-lead multiple bonding were prepared and structurally characterized. Using the m-terphenyl ligands C6H3-2,6-(C6H2-2,4,6-tBu3)2 (ArtBu6) and C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2 (AriPr8) gave multiply bonded structures in the solid state. Calculations in collaboration with Prof. Stefan Grimme, Markus Bursch, Jakob Seibert, and Leonard Maurer showed that dispersion energies also contributed significantly to the stability of these molecules. Chapter 3 describes stable m terphenyl lead(II) hydrides that were isolated in the preparation of the diplumbynes.Chapter 4 describes the metathesis reactions of heavy group 14 element alkyne analogues of Ge, Sn, and Pb with Mo-Mo single and triple bonds. These compounds reversibly dissociate in solution to monomeric radicals. By their direct reaction with (CO)3(η5-C5H5)Mo–Mo(η5-C5H5)(CO)3 and (CO)2(η5-C5H5)Mo≡Mo(η5-C5H5)(CO)2¬¬, the energetically favored group 14 element-Mo bonds are formed. Chapter 5 describes the synthesis of the first isolated species with a one-coordinate aluminum atom. The sterically demanding AriPr8 ligand stabilizes this geometry. Nonetheless, calculations showed that a dimer, the dialuminene AriPr8AlAlAriPr8, is slightly favored. This is supported by the facile reactivity of :AlAriPr8 with H2. In Chapter 6 the reaction of :AlAriPr8 with several organoazides is described. When the m-terphenyl azide ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2 is used, the first compound with an Al-N triple bond AriPr8AlNArMe6 was isolated. The attractive dispersion forces between the two terphenyl substituents on the Al and N atoms contribute a stabilization energy that is on the same order of magnitude as the Al-N π-type bonds in the molecule. Chapter 7 describes a new route to dialuminenes of the formula RAl=AlR. These species are highly reactive towards arene solvents in which they are soluble. By using a terphenyl ligand substituted by the -SiMe3 group, C6H2-2,6-(C6H3-2,6-iPr2)2-4-SiMe3 (AriPr4-4-SiMe3) we anticipated increasing the solubility of the dialuminene in solvents with which it would not react. Direct reduction of the iodide precursors to 4-SiMe3AriPr4Al=AlAriPr4-4-SiMe3 failed, so a new route through the comproportionation of Al(Et2O)I2AriPr4-4-SiMe3 or (AlIAriPr4-4-SiMe3)2 with the dialuminyne salt Na2(AlAriPr4-4-SiMe3)2 was used. In hexanes or ether, this reaction mixture turns deep purple before rapidly decomposing. However, in benzene the dialuminene-benzene [2+4] cycloaddition complex is stoichiometrically obtained from the comproportionation reaction.

This dissertation focuses on the synthesis and characterization of ferriotetrylenes, which are complexes featuring a two-coordinate E(II) (E = Ge, Sn, or Pb) σ-bonded to FeCp(CO)2 (Cp = η5-C5H5) and a terphenyl group. The reactivity of the ferriotrylenes with ammonia is also described. Additionally, the synthesis and characterization of the biscarboranyl complexes (bc)Sn·THF, [(bc)Sn]2KCl, and bc-CH=CH-bc (bc = 1,1′-bis(o-carborane) are also described. Single crystal X-ray crystallography was employed to establish the structural details of the solid-state structures. NMR spectroscopic studies (1H, 11B, 13C, 119Sn, 207Pb) were employed for the spectroscopic characterization of the novel complexes and the characterization of the products of their reactions with ammonia. Spectroscopic methods were also used to determine the energetics of the reversible reaction with ammonia. New compounds were additionally characterized by UV-visible and infrared spectroscopy.The ferriogermylene ArMe6GeFeCp(CO)2 (ArMe6 = −C6H3-(C6H2-2,4,6-CH3)2) was synthesized by salt metathesis of the terphenyl germanium chloride (ArMe6GeCl) with the potassium salt of the iron cyclopentadienyl dicarbonyl anion (K[FeCp(CO)2]). In the solid state, ArMe6GeFeCp(CO)2 can form one of three crystalline polymorphs in green, red, or dichroic red-green crystals. Regardless of polymorph, ArMe6GeFeCp(CO)2 is spectroscopically and structurally similar to its more substituted derivative AriPr4GeFeCp(CO)2 (AriPr4 = −C6H3-(C6H3-2,6-iPr)2). Additionally, it was shown to react with H2O to afford the oxidative addition product ArMe6Ge(OH)(H)FeCp(CO)2. The complexes ArGeFeCp(CO)2 (Ar = ArMe6 or AriPr4) were shown to react with ammonia to afford the insertion products ArGe(NH2)(H)FeCp(CO)2 (Ar = ArMe6 or AriPr4). Salt metathesis was also employed in the synthesis of the two tin derivatives ArMe6SnFeCp(CO)2 and ArMe6SnFeCp*(CO)2 (Cp* = η5-C5Me5). The compound ArMe6SnFeCp(CO)(PMe3) was produced through a phosphine-carbonyl exchange reaction. Spectroscopic and structural comparisons of these ferriostannylenes and the more substituted derivatives ArSnFeCp(CO)2 (Ar = AriPr4 or AriPr6) showed the effect of the substituents on the central Sn atom. Increasing the size of the alkyl substituents on the aryl groups (aryl = terphenyl or cyclopentadienyl) narrows the interligand angle at Sn and causes a corresponding bathochromic shift of the HOMO→LUMO transition in the UV-vis spectra. Changing a CO ligand on the Fe fragment to PMe3 widens the interligand angle at Sn while causing a bathochromic shift of the HOMO→LUMO transition in the UV-vis spectrum. The ferriostannylenes ArSnFeCp(CO)2 (Ar = ArMe6 or AriPr4) were observed to react reversibly with ammonia. Visually, the reactions followed a similar color pattern to the reaction of the ferriogermylenes ArGeFeCp(CO)2 (Ar = ArMe6 or AriPr4) with ammonia. Variable temperature 1H NMR studies determined that the free energy of the reversible reaction of AriPr4SnFeCp(CO)2 with ammonia was essentially thermoneutral and are in good agreement with DFT calculations made by the Goicoechea research group on a phosphine system that displayed a related thermoneutral, reversible activation of ammonia. The ferrioplumbylenes ArPbFeCp(CO)2 (Ar = ArMe6 or AriPr4) were synthesized in the same manner as the Ge and Sn congeners to complete the series. Spectroscopic and structural comparisons of the ArEFeCp(CO)2 (E = Ge, Sn, or Pb; Ar = ArMe6 or AriPr4) series revealed a pattern that is reflected in the ferriotetrylene reactivities towards ammonia. The compound ArMe6PbFeCp(CO)2 was inert in the presence of ammonia.

This dissertation describes the reactivity a series of terphenyl-supported heavier group 14 germylenes and stannylenes toward fundamentally important small molecules. The germylenes and stannylenesthat are used in this thesis are Ge(ArMe6)2, Ge(AriPr4)2, Ge(AriPr6)2, Sn(ArMe6)2, Sn(AriPr4)2, and Ge(AriPr6)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2, AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2 and AriPr6 = C6H3-2,6(C6H2-2,4,6-iPr3)2). The solid-state structures of their reaction procuts were determined by single X-ray spectroscopy. Other characterization method includes nuclear magnetic resonance spectroscopy, UV-visible spectroscopy, infrared spectroscopy, melting point analysis, and electron paramagnetic spectroscopy. All operations were carried out under anaerobic and anhydrous conditions using modified Schlenk techniques. All solvents were dried over alumina columns, stored over a sodium or potassium mirror, and degassed before use. A summary of the previous investigations of the synthesis and reactivity of tetrylenes is described in Chapter 1. Chapter 2: The diarylstannylene, :Sn(AriPr4)2 (AriPr4 = C6H3-2,6-(C6H3-2,6- iPr 2)2), undergoes C-H metathesis with toluene, m-xylene or mesitylene in solutions of these solvents at 80 °C. The products afforded [AriPr4Sn(CH2Ar)]2 (Aryl= C6H5 (1a), C6H4-3-Me (1b), C6H3-3,5- Me2(1c)) were characterized via 1H , 13C and 119Sn NMR, UV-vis and IR spectroscopy, and by X-ray crystallography for 1a and 1b. A stoichiometric amount of the arene, AriPr4H, was also produced in these reactions. The use of EPR spectroscopy indicated the presence of a new type of one-coordinate, tin-centered radical, ꞏSnAriPr4, resulting from Sn-C bond cleavage in :Sn(AriPr4)2. Chapter 3: It is shown that the tin-tin triple bond in the distannyne AriPr4SnSnAriPr4 (AriPr4 = C6H3-2,6-(C6H3-2,6- iPr 2)2), undergoes reversible cleavage in deuterated toluene to afford two ꞏSnAriPr4 radicals as shown by 1H NMR and EPR spectroscopy. Variable temperature 1H NMR data afforded an enthalpy of dissociation of ΔHdiss=17.2±1.7 kcal mol-1 via van‘t Hoff analysis. The EPR and 1H NMR data indicated that the Sn-Sn bond in AriPr4SnSnAripr4 is weak and is consistent with the Sn-Sn bond being a charge-shift bond. Chapter 4: In this Chapter, the detection of tin and germanium radicals during the photolysis/thermolysis of diarylstannylene SnR2 and diarylgermylene GeR2 (R = AriPr4 = C6H3-2,6-(C6H3-2,6- iPr2)2 or AriPr6 = C6H3-2,6-(C6H2-2,4,6- iPr3)2 ), by using EPR spectroscopy complemented with theoretical calculations are described. The trapped tin radical is a one-coordinated S = 1/2 Sn(I) radical, i.e., : Sṅ R (R = AriPr4 or AriPr6), with g tensor values of [2.031, 1.980, 1.940] (giso= 1.984). In contrast, the trapped germanium radical is a pseudo-planar S = 1/2 Ge(III)-hydride species, i.e., ꞏGeHRR’ (R = AriPr4 or AriPr6 , R’ is a quaternary carbon), with g tensor values of [2.029, 2.003, 1.989] (giso = 2.007) and a strong 1H-hyperfine tensor [-23.0, -20.5, -31.5] MHz for the hydride. The generation of this Ge(III)-hydride could be due to the greater reactivity Ge(I) radical intermediate (: Gė R) and the greater strength of a Ge-H bond. The Ge(III)-hydride species arise from the insertion of the active Ge(I) radical intermediate in a C-H bond. This chapter provides insights into the radical mechanistic understanding of the heavier group 14 element tetrylenes chemistry. Chapter 5: It is shown that the diarylstannylenes, Sn(AriPr4)2 and Sn(AriPr6)2, (AriPr4 = C6H3- 2,6-(C6H3-2,6- iPr 2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6- iPr3)2), undergo a facile migratory insertion reaction with ethylene at 60 °C to afford the alkyl aryl stannylenes AriPr4SnCH2CH2AriPr4 and AriPr6SnCH2CH2AriPr6 these products were characterized via 1H , 13C and 119Sn NMR, UV-vis and IR spectroscopy, as well as by X-ray crystallography. Quantum mechanical calculations were performed by our collaborator Dr. Guo, and two potential mechanisms were identified. Chapter 6: The diarylgermylenes Ge(ArMe6)2 and Ge(AriPr4)2 (ArMe6=C6H3-2,6-(C6H3-2,4,6- Me3)2), AriPr4=C6H3-2,6-(C6H3-2,6-iPr2)2) were shown to react reversibly with ethylene. It is shown that the more sterically crowded Ge(AriPr4)2 also reversibly binds propylene. The germirane products Ar2GeCH2CHR) (Ar,R = ArMe6, H (1a), AriPr4, H (1b) and AriPr4, Me (1c) were characterized via 1H and 13C NMR spectroscopy and by X-ray crystallography in the case of 1b. Thermolysis of Ge(AriPr4)2 under ethylene resulted in Ge-C bond homolysis and the formation of the digermene [(AriPr4)Ge(Et)]2(1d). The thermodynamic parameters of the reactions were determined by variable temperature 1H NMR spectroscopy. Chapter 7: The diarylgermylene, Ge(ArMe6)2 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2), were shown to react reversibly with the four unstrained alkynes: 3-hexyne, diphenylacetylene, trimethylsilylacetylene and phenylacetylene at ambient temperature in toluene. The germirene products, (ArMe6)2GeC(R)=C(R’) (R, R’ = Et, Et (1a), Ph,Ph (1b), H, SiMe3 (1c) and H, Ph (1d) were characterized via 1H and 13C NMR spectroscopy and by X-ray crystallography in the case of 1a and 1d. The thermodynamic parameters of the reactions were determined by variable temperature 1H NMR spectroscopy and the experimental Gibbs free energies indicated their near thermoneutrality. Chapter 8: The facile heterodehydrocoupling of a range of primary or secondary amines and even ammonia with pinacolborane (HBPin) was accomplished using {ArMe6Sn(μ-OMe)}2 (1, ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) as a pre-catalyst for a catalytically active tin(II) hydride. The more sterically hindered pre-catalyst {2, AriPr4Sn(μ-OMe)}2 (AriPr4 = C6H3-2,6-(C6H3-2,6- iPr2)2) facilitated the dehydrocoupling only of primary amines with HBPin, but at an increased rate relative to the less crowded {ArMe6Sn(μ-OMe)}2. Also presented is {ArMe6Sn(μ-NEt2) (3), which can be converted into the structurally characterizable {ArMe6Sn(μ-NEt2)(μ-H)SnArMe6} (4) via the addition of pinacol borane. This, alongside stoichiometric studies, gives insight into the mechanism of the catalysis. Chapter 9: The diarylgermylene Ge(ArMe6)2 (ArMe6=C6H3-2,6-(C6H2-2,4,6-Me3)2) was shown to react with azobenzene at room temperature to yield the Ge(IV) diamido products, (ArMe6)2Ge{N(H)(Ph)-o(Ph)(H)N}(1a) and (ArMe6)2Ge{N(H)-o-C6H4N(Ph)}(1b) which were characterized via 1H and 13C NMR spectroscopy and by X-ray crystallography. Treatment of Ge(ArMe6)2 with bulkier diazenes,1,2-bis(2,6-diethylphenl)diazene or 1,2-bis(1,3,5- trimetylphenyl)diazene, even at elevated temperature did not afford N-N bond cleavage and only C-H activation of the germylene was observed. Use of the analogous tin species Sn(ArMe6)2 under the same condition afforded no reactions.

The purpose of the first part of this thesis is to describe how dispersion energy donor ligands derived from 1-bromo-2,4,6-tricyclohexylbenzene (BrC6H2-2,4,6-Cy3) can effect the stabilization of low-valent transition metal and main group compounds. Thus, reactions of 2,4,6-tricyclohexylphenol with [M{N(SiMe3)2}2]2 (M = Mn(II), Fe(II), Co(II)) at room temperature in hexanes afforded the dimeric species [M(OC6H2-2,4,6-Cy3)2]2 (M= Mn(II), Fe(II), Co(II)) in high yield as crystalline species. Use of the sterically similar ligand HOC6H3-2,6-Pri2 (Pri = isopropyl) gave trimeric species [M(OC6H3-2,6-Pri2)2]3 (M = Fe(II), Co(II)) and implicates the dispersion energy donor capabilities of the phenol HOC6H2-2,4,6-Cy3 as the driving force for the formation of dimeric rather than trimeric species. While the Mn(II) and Fe(II) aryloxides are thermally stable, the corresponding Co(II) derivative rearranges to form a dimeric Co(II) semiquinone complex when heated under dynamic vacuum to temperatures above ca. 180 oC. Analogous reactions of HOC6H2-2,4,6-Cy3 with main group bis(trimethylsilyl)amides M{N(SiMe3)2}2 (M = Ge(II), Sn(II), and Pb(II)) gave the dimeric tetrel(II) aryloxides [M(OC6H2-2,4,6-Cy3)2]2. For Ge(II), stirring the reaction for longer than ca. 30 minutes at room temperature in hexane allows the isolation of the rearranged Ge6O8 cluster [Ge6(μ3-O)4(μ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 which traps in situ generated ammonia in non-coordinating positions through the dispersion energy donor interactions provided by the cyclohexyl groups of -OC6H2-2,4,6-Cy3.The arylthiolates [M(SC6H2-2,4,6-Cy3)2]2 (M = Ge(II), Sn(II), Pb(II)) were synthesized in an analogous manner to the tetrel(II) aryloxides by the addition of HSC6H2-2,4,6-Cy3 to the M(II) bis(trimethylsilyl)amides. They are the first examples of dimeric M(II) arylthiolates of Ge(II) and Sn(II). Also, the Pb(II) species is the first arylthiolate isolable in the absence of donor ligands or Lewis bases. Previous attempts to obtain a Ge(II) arylthiolate using the thiol HSC6H2-2,4,6-Pri3 gave the Ge(IV) hydride HGe(SC6H2-2,4,6-Pri3)3. DFT calculations revealed that an increase in the dispersion energy stabilization provided by -SC6H2-2,4,6-Cy3 in the species [Ge(SC6H2-2,4,6-Cy3)2]2 prevents the formation of a Ge(IV) hydride analogous to that observed when the thiolato ligand -SC6H2-2,4,6-Pri3 was used. A concentration dependent monomer-dimer equilibrium is evident in benzene solutions of [Ge(SC6H2-2,4,6-Cy3)2]2, despite the large increase in dispersion energy stabilization. The Ge(II) and Sn(II) arylthiolates are not isostructural with their aryloxo congeners and have a cis arrangement of the ligands in the solid state. In contrast, the Pb(II) thiolate is isostructural with the Pb(II) aryloxo congener and crystallizes with a trans arrangement of the -SC6H2-2,4,6-Cy3 ligands. The final section of this thesis provides detail on the synthesis and isolation of Ni(I) and Ni(II) bis(trimethylsilyl)amides that were isolated during pursuit of the solid-state structure of the highly unstable species Ni{N(SiMe3)2}2. The use of the bis(trimethylsilyl)amide K{N(SiMe3)2} as transfer agent was reported to give intractable solids when reacted with NiCl2 in diethyl ether. This prompted a reinvestigation of the use of this transfer agent in the synthesis and isolation of new Ni(II) bis(trimethylsilyl)amides. The reaction of K{N(SiMe3)2} with NiI2 in Et2O gave the three new complexes [K][Ni{N(SiMe3)2}3], [K][Ni{N(SiMe3)2}2], and [K(THF)2][Ni{N(SiMe3)2}3]. The use of NiCl2(DME) (DME = 1,2-dimethoxyethane) instead of NiI2 as the nickel source gave [K(DME)][Ni2{N(SiMe3)2}3]. The isolation of the Ni(I) complexes [K][Ni{N(SiMe3)2}2] and [K(DME)][Ni2{N(SiMe3)2}3] highlights both the tendency for K{N(SiMe3)2} to function as a reducing agent and the sensitivity and unpredictable nature of the Ni(II) bis(trimethylsilyl)amido derivatives. Introduction of adventitious O2 to solutions of [K][Ni{N(SiMe3)2}2] gave the first nickel inverse crown ether (ICE) species [K2][O(Ni{N(SiMe3)2}2)2], which is one of just four known ICE complexes of the 3d metals. While the Ni(I) species can be isolated as crystalline solids from the disproportionation of the Ni(II) species, the corresponding Ni(III) products were not readily isolable under the employed reaction conditions.