Acceptor-Substituted Cyclopentadienyl Compounds

Efficient methodologies for the synthesis of acceptor-substituted perfunctionalized cyclopentadienyl (Cp) compounds were investigated. A facile multigram, one-pot synthesis of [FeC10(HgO2CC3H7)10] from ferrocene and Hg(O2CC3H7)2 is reported. In the corresponding compound, the Hg-C bonds are inert towards oxygen, moisture and even strong Brønsted acids like trifluoroacetic acid and [C5F5NH][SbF6]. Instead, protonation of the carboxylic groups is observed yielding [FeC10(HgO2CCF3)10] and [FeC10Hg10(C5F5N)n][SbF6]10. In the compound [FeC10Hg10(C5F5N)n][SbF6]10, the labile C5F5N ligands are readily displaced by MeCN or tetrahydrothiophene (THT) to afford rare examples of organometallic decacations [FeC10(HgL)10][SbF6]10 (L = MeCN, THT). Electrochemical investigations on the (soluble) permercurated compounds reveal increasing redox potentials of the corresponding Fe(II)/Fe(III) redox couples with increasing Lewis acidity of the Hg-sites. The isolation of the oxidized forms was realized by reaction with [NO]+ or [NO2]+ salts or MoF6. Furthermore, the first crystallographic characterization of permetalated aromatic compounds [FeC10(HgX)10] (X = Cl, O2CCF3, O2CCCl3), [FeC10(HgTHT)10][SbF6]10 and [FeC10(HgMeCN)10][SbF6]10[MoF6] is presented. Complete halodemercuration is observed in the reaction of [FeC10(HgO2CC3H7)10] with K[Br3] followed by halogenation with FeBr3 and elemental Br2. An oxidation potential of E1/2 = 1.1V renders the corresponding ferrocenium cation as potent oxidizing agent. The isolation is realized by reaction of [FeC10Br10] with AsF5. Further functionalization of [FeC10Br10] is achieved by metalation with elemental Mg or by lithium-halogen-exchange with tBuLi. Quenching experiments with dimethylsilylchloride (DMSCl) yielded polysilylated compounds. Full functionalization was achieved after multiple metalation-silylation sequences. The resulting product [FeC10DMS10] displays the first example of a persilylated metallocene. A series of polysilylated derivatives [FeC10DMSnH10-n] (n = 7, 8, 9, 10) is analyzed by CV, single-crystal XRD, NMR and UV/VIS spectroscopy to evaluate the effect of silylation on the electronic properties of metallocenes. The obtained data are supported by quantum-chemical calculations. In the context of perhalogenated Cp compounds, the reaction of C5X6 (X = Cl, Br) with AsF5 and SbF5 is investigated. Here, the formation of unprecedented [2+2]-cycloaddition products of two Cp cations [C5X5]+ is observed. The obtained dications [C10X10]2+ are analyzed by XRD and NMR spectroscopy. DFT calculations reveal that the dimerzation to [2+2]- instead of [2+4]-products is thermodynamically preferred due to the formation of two allylic p-electron systems. Furthermore, in cooperation with the group of Prof. Dr. Schulz the electrochemical properties of [C5(C6F5)5]+ are presented

Noncovalent Interactions in Halogenated Pyridinium Salts of the Weakly Coordinating Anion [Al(OTeF5)4]–

The synthesis and the first structural characterization of the halogenated pyridinium salts [C 5 F 5 NH] + , [C 5 F 4 ClNH] + , [(C 5 F 5 N) 2 H] + , [(C 5 Cl 5 N) 2 H] + of the weakly coordinating anion (WCA) [Al(OTeF 5 ) 4 ] − , showing noncovalent interactions in the solid state, are presented. The salts were characterized by the multinuclear NMR and IR spectroscopy as well as X-Ray diffraction. Hirshfeld surface analysis and solid state structures reveal various intermolecular anion-π and σ-hole interactions between the corresponding halogenated pyridinium cations and the anion [Al(OTeF 5 ) 4 ] −

Synthesis and Characterization of Silicon Polyoxolenes

Tris(catecholato)silicate dianions, a compound class that is already known for over a century, can be readily prepared by reacting sand with catechol under basic conditions. Strikingly, the two-electron-oxidized derivative – silicon tris(perchloro)dioxolene 1Cl – has been recently accessed, representing a thermally stable, neutral triplet diradical and the first non-metal complex with redox-active and mixed-valence substituents. In the present work, the redox properties of 1Cl are investigated and by the synthesis of the corresponding monoradical anion [1Cl]•−, the redox series of tris(catecholato)silicates in general is completed. With cyclic voltammetry the redox potentials E1/2 = 0.43 V and 0.88 V (vs. Fc/Fc+) were finally determined. Comparing the redox potentials of 1Cl with free tetrachloro-o-benzoquinone, a tremendous shift of about 1.2 V becomes apparent. Moreover, 1Cl is applicable as efficient redox catalyst. By varying the quinone ligands and the silicon source, further homo- and heteroleptic derivatives are prepared. Variable temperature EPR measurements disclose the existence of diradicals with a triplet ground state. With a more profound understanding of the monomeric species, the synthesis is extended to higher nuclearity. A straightforward approach is established by introducing substituted 2,5-dihydroxy-p-benzoquinone (H2dhbqY) as [dhbqY][Na@15c5]2 (Y = Cl, Br, Ph, NO2) salts and mixing with bis(catecholato)silanes 2X (X = Cl, Br, CF3, iPr) to obtain the dinuclear species [4X,Y][Na@15c5]2, which are robust to coordinating environments. By selective combination of more electron-rich 2X and electron-poor dhbq linkers diradicaloid complexes [4X,Y]2− (X = Cl, iPr and Y = Cl, Br, NO2) were obtained and characterized. The opposite extreme with the smallest diradical character was accomplished by combining electron-poor 2CF3 and electronrich dhbqPh. The underlying design principle is further disclosed by computational analyses. Conclusively, this one-step protocol grants access to dimeric silicon polyoxolenes with control over and fine-tuning of the spin ground state. Lastly, preliminary results are obtained for the trimeric structures by implementing the six-fold deprotonated tritopic linker 2,3,6,7,10,11-hexahydroxytriphenylene (H6hhtp) with 2Cl. The results gathered in this work present a fundamental understanding of silicon-bridged polyoxolenes and thus are valuable extensions based on a non-metal main group element to known works based on transition metals

Quaternary Ammonium Salts and Brønsted Superacids based on Weakly Coordinating [Al(OTeF5)4]− Anion

A series of tetraalkylammonium tetrakis(pentafluoroorthotellurato)aluminate salts [NAlk4][Al(OTeF5)4], Alk4 = –(CH3)4, –(C2H5)4, –(C2H5)3CH3, –(C3H7)4, –(C4H9)4 were described, characterized and some identified as ionic liquids. The Brønsted superacid [o-C6H4F2-H][Al(OTeF5)4] was applied for the protonation of very weak bases – halogenated pyridines C5F5N, C5F4ClN, C5Cl5N and C5H2F2N and C5H4BrN – to yield the corresponding [C5F5N-H][Al(OTeF5)4], [(C5F5N)2H][Al(OTeF5)4], [C5F4ClN-H][Al(OTeF5)4], [(C5Cl5N)2H][Al(OTeF5)4], [C5H4BrN-H][Al(OTeF5)4] and [C5F3H2N-H][Al(OTeF5)4] salts. The obtained crystal structures in the solid state of these salts show rare non-covalent interactions like anion-π and σ-hole interactions between pyridinium cations and the [Al(OTeF5)4]– weakly coordinating anion. The reaction of commercial refrigerant HFO-1234yf with arene-based Brønsted superacids lead to selective C(sp3)-F bond activation and resulted in the typical trifluoroallyl-substituted arenes, which are Friedel-Crafts like products

Carboranes: Engineering Ligands and Catalysts

Carborane anions have been increasingly utilized as a vital tool in the study of reactive compounds as a result of their high stability and weakly coordinating properties. These unique properties has anchored them into the toolbox of any chemist pursing unique and novel chemistry. Though they have been mainly used as counter anions to stabilize reactive cations, their application in organometallic chemistry is still in its infancy. In this report, we provide an in depth study on their impact towards organometallic chemistry. Specifically, we studied their reactivity with the trityl cation and found that it does not react the way it has historically been explained. Moreover, we sought to use them as phosphine ligand substituents. Their use in the hydroamination of alkynes with gold was explored. Furthermore, their incorporation into a series of zwitterionic Ru complexes were examined. We also investigated how carboranyl phosphines affect the activity of Drent-type palladium polymerization of ethylene. Lastly, we probed an exotic palladium dimer with its reactivity with ethylene

From Lewis Superacidic Aluminum Pentafluoroorthotellurates to Perfluorinated Tritylium and Fluoronium Ions

The properties and reactivity of Lewis superacidic aluminum pentafluoroorthotellurates are investigated. An improved synthesis for the dimeric [Al(OTeF5)3]2 was developed, yielding a pure product with an enhanced thermal stability. Different solvent adducts were synthesized, resulting in monomeric complexes of the Lewis acid with up to three solvent molecules attached. The complexes of Al(OTeF5)3 with toluene, fluorobenzene and sulfuryl chloride fluoride remained Lewis superacidic, as quantum-chemical calculations confirmed. Additionally, the high Lewis acidity of [Al(OTeF5)3]2 and its solvent adducts were further verified by experimental methods. Two different routes for the synthesis of the perfluorinated trityl cation [C(C6F5)3]+ were established. One utilizes the Lewis superacid [Al(OTeF5)3(OSOClF)2], the other the corresponding Brønsted superacid [H–C6H4F2][Al(OTeF5)4]. A crystallographic characterization of this cation in conjunction with the weakly coordinating anion [Al(OTeF5)4]− was achieved for the first time. These routes finally give access to the perfluortrityl cation in SO2ClF and organic solvents such as ortho-difluorobenzene. This improved handling enabled insights into the reactivity of this cation as hydride abstractor and oxidation reagent, which was proven by experimental and theoretical methods. Organic divalent fluoronium ions were only investigated by spectroscopic studies, while a characterization in the solid state so far did not yield success. In this thesis, the synthesis and crystallographic analysis of a symmetrical [C–F–C]+ fluoronium ion is reported. The vibrational spectrum of the fluoronium salt is discussed and the nature of the bonding situation in this type of cations are quantum-chemically studied and compared with heavier halonium homologues. Besides the isolation and characterization of elusive cations with strong Lewis acids, the synthesis of a novel solid Lewis superacid is reported. Hereby, the reaction of a mixture of AlCl3 and [Al(OTeF5)3]2 with CCl3F leads to an anion-doped aluminum chlorofluoride AlCl0.1F2.8(OTeF5)0.1. This material was studied by PDF analysis, EXAFS and MAS NMR spectroscopy, confirming an intact OTeF5 group. A reaction with CD3CN and subsequent IR spectroscopy revealed the Lewis superacidic nature of the material. Lastly, the catalytic activity of the material in dehydrofluorination reactions was tested.Die Eigenschaften und die Reaktivität von Lewis-supersauren Aluminiumpentafluoroorthotelluraten wurden untersucht. Es wurde eine verbesserte Synthese für dimeres [Al(OTeF5)3]2 entwickelt, die ein reineres Produkt mit erhöhter thermischer Stabilität ergibt. Es wurden verschiedene Lösungsmitteladdukte syn- thetisiert, wobei monomere Komplexe der Lewis-Säure mit bis zu drei gebundenen Lösungsmittelmolekülen erhalten wurden. Die Komplexe von Al(OTeF5)3 mit Toluol, Fluorbenzol und Sulfurylchloridfluorid gelten immernoch als Lewis-Supersäuren, was durch quantenchemische Berechnungen bestätigt wurde. Darüber hinaus wurde die hohe Lewis-Azidität von [Al(OTeF5)3]2 und seinen Lösungsmitteladdukten durch experimentelle Methoden weiter verifiziert. Es wurden zwei unterschiedliche Routen zur Synthese des perfluorierten Tritylkations [C(C6F5)3]+ entwickelt. Die erste Route nutzt die Lewis-Supersäure [Al(OTeF5)3(OSOClF)2], während die zweite Route die korrespondierende Brønsted Supersäure [H–C6H4F2][Al(OTeF5)4] verwendet. Das schwach koordinierende Anion [Al(OTeF5)4]− ermöglichte die kristallographische Charakterisierung dieses Kations mittels Einkristall-Röntgenstrukturanalyse. Die vorgestellten Synthesrouten führen so erstmalig zur Handhabung des Perfluortrityl-Kations in SO2ClF und organischen Lösungsmitteln wie ortho-Difluorbenzol. Dies erlaubte Einblicke in die Reaktivität dieses Kations als Hydridabstraktor und Oxidationsreagenz, was mit experimentellen und theoretischen Methoden nachgewiesen wurde. Organische, divalente Fluoroniumionen wurden bisher nur durch spektroskopische Studien untersucht, während eine Charakterisierung im festen Zustand bisher nicht möglich war. In dieser Arbeit wird über die Synthese und kristallographische Analyse eines symmetrischen [C–F–C]+ Fluoroniumions berichtet. Darüber hinaus wird das Schwingungsspektrum des Fluoroniumsalzes diskutiert und die Bindungssituation in dieser Art von Kation quantenchemisch untersucht und mit schwereren Halonium-Homologen verglichen. Neben der Isolierung und Charakterisierung von schwer-fassbaren Kationen mit starken Lewis-Säuren wird über die Synthese einer neuartigen festen Lewis-Supersäure berichtet. Dabei führt die Reaktion einer Mischung aus AlCl3 und [Al(OTeF5)3]2 mit CCl3F zu einem anionen-dotierten Aluminiumchlor-fluorid AlCl0.1F2.8(OTeF5)0.1. Dieses Material wurde mittels PDF-Analyse, EXAFS- und MAS-NMR- Spektroskopie untersucht, wodurch die Intakthaltung der OTeF5 Gruppe bestätigt werden konnte. Eine Reaktion mit CD3CN und anschließende Untersuchung mittels IR-Spektroskopie zeigten die Lewis-supersauren Eigenschaften des Materials. Schließlich wurde die katalytische Aktivität des Materials in Dehydrofluorierungsreaktionen getestet

Tetrel Bonding in Anion Recognition: A First-Principles Investigation

Twenty-five molecule-anion complex systems [I4Tt...X-] (Tt = C, Si, Ge, Sn and Pb; X = F, Cl, Br, I, At) were examined using density functional theory (wB97XD) and ab initio (MP2 and CCSD) methods to demonstrate the ability of the tetrel atoms in molecular entities, I4Tt, to recognize the halide anions when in close proximity. The tetrel bond strength for the [I4C...X-] series, and [I4Tt...X-] (Tt = Si, Sn; X = I, At), was weak-to-moderate, whereas that in the remaining 16 complexes was dative tetrel bond type with very large interaction energies and short Tt...X close contact distances. The basis set superposition error corrected interaction energies calculated with the highest-level theory applied, [CCSD(T)/def2-TZVPPD], ranged from -3.0 to -112.2 kcal mol-1. The significant variation in interaction energies was realized as a result of different levels of tetrel bonding environment between the interacting partners at the equilibrium geometries of the complex systems. Although the wB97XD computed intermolecular geometries and interaction energies of [I4Tt...X-] were close to those predicted by the highest level of theory, the MP2 results were shown to be misleading for some of the molecule-anion complex systems investigated. To provide insight into the nature of the intermolecular chemical bonding environment in the 25 molecule-anion complexes investigated, we discussed the charge density based topological and isosurface features that emanated from the application of quantum theory of atoms in molecules and independent gradient model approaches, respectively

Synthesis of Carborane Pincer Complexes and Exploration Of The Reactivity of Metal-Boron Bonds

Exploration of transition metal complexes with metal-boron bonds for the cooperative bond activation of small molecules in catalysis is one of the recent developments in novel synthetic strategies. The use of boron clusters as a modular platform for the formation of metal-boron bond has been successfully utilized by our and other groups. Carboranes are icosahedral boron-carbon molecular clusters that have gained attraction as multifunctional ligands due to their unique geometry, electronic properties, and versatility of functionalization methods. Their 3-D structure exerts a steric bulk around the exohedral substituent, either metal or non-metal center. Furthermore, due to the cluster geometry, five of the cluster atoms are always in proximity with the exohedral metal center vertex resulting in the possibility of 3-center-2-electron B–H…M bridging interactions that support the 2-center-2-electron metal-boryl -bond. The use of rigid tridentate pincer ligands with carborane backbone and heteroatom donor groups allowed the synthesis of transition metal B-carboranyl complexes through the activation of relatively inert cluster B–H bonds. The unique geometry of the cluster with the pincer donor arms has resulted the highly strained, electron rich metal-boron bonds that have the potential to act as nucleophilic reaction centers in the bond activation of small molecules. Transition metal benzyne complexes have been intensively studied due to their ability of small molecule activation. The benzyne chemistry inspired the synthesis of the transition metal carboryne complexes, which can be considered as 3-D inorganic boron-based analogues of benzynes, in many cases similar reactivity. The highly strained and electron-rich metal-boron bonds in the three-membered (BB)\u3eRu metallacycle can act as nucleophilic reaction centers in bond activation of small molecules. In this dissertation, a novel synthetic stratergy was employed in synthesizing (BB)\u3eRu carboryne complexes via neutral ruthenium carborane dichloride complex as an intermediate, which allowed to install several classes of auxiliary ligands in trans- position to boryls: nitriles and phosphines. The replacement of strongly bound π-accepting carbonyls by these predominantly σ-donating and more labile ligands opened several new reactivity manifolds. New examples of the reactivity of the ruthenium carboryne bis(benzonitrile) complex in C-C bond activation of terminal alkynes, C-H bond activation of the phenyl group, N=N bond activation of azides and C-H and C-C bond activation of aldehydes wasstudied, in addition to the unique reactivity observed in ruthenium carboryne bis(diphenylphosphine) complex for the aldehydes. In addition, the presence of an exohedral 2-center-2-electron B-Ru bond and a 3- center-2-electron B-H…Ru bond in the same metal complex with the metal hydride resulted in catalytic activity in the transfer hydrogenation reaction. A series of boryl hydride complexes (POBOP)Ru(H)(L) [L=PPh3, PHPh2, PEt3] were synthesized, which were used as a platform for the assembly of heterometallic complexes. Functionalization of the carbon vertex of the carborane cluster is carried out using alkali metal-containing strongly basic reagents to generate carbon-centered nucleophiles. The careful utilization of metal chelating ligands to capture and remove the metal center from the metalated carbon vertex of the cluster generated strong carbon-centered nucleophiles with uncompensated negative charge on the carbon atom in these separated ion pairs. The alkali metal cation was separated from the deprotonated cluster using metalchelating crown ethers, which allowed us for the first time to isolate, structurally and spectroscopically characterize the highly nucleophilic “naked” 3-D carborane carbanion. Analogously, the doubly deprotonated 1,1′-bis(o-carborane) yielded similar dianionic “naked” carbanionic species serving as the first example of carbdianion

Structure-reactivity studies on hypervalent square-pyramidal dithieno[3,2-b:2’,3’-d]phospholes

A series of neutral pentacoordinate dithieno[3,2-b:2’,3’-d]phosphole compounds were synthesized by [4+1] cycloaddition with o-quinones. Counter to the expected trigonal bipyramidal geometry, the luminescent hypervalent dithienophospholes exhibit square pyramidal geometry with inherently Lewis acidic phosphorus center that is stabilized via supramolecular π-stacking interactions in the solid state and in solution. Due to their Lewis-acid character, the compounds react with nucleophiles, suggesting their potential as mediator in organic transformations. The new species thus present an intriguing structural plaform for the design of neutral P(V) Lewis acids with useful reactivities.NSERC, CFI, Canada Research Chair

A Short, Versatile Route Towards Benzothiadiazinyl Radicals

A family of substituted 1,2,4-benzothiadiazine 1-chlorides have been prepared by treatment of N-arylamidines in neat thionyl chloride at reflux. The S(IV) 1-chlorides are readily reduced under mild conditions to persistent 1,2,4- benzothiadiazinyl radicals which have been characterised by EPR spectroscopy and cyclic voltammetry. Crystallographic studies on isolated radicals indicate that the radicals dimerise via pancake bonding in the solid-state, resulting in spin-pairing and net diamagnetism