Computing the Margin of Victory in Preferential Parliamentary Elections

We show how to use automated computation of election margins to assess the number of votes that would need to change in order to alter a parliamentary outcome for single-member preferential electorates. In the context of increasing automation of Australian electoral processes, and accusations of deliberate interference in elections in Europe and the USA, this work forms the basis of a rigorous statistical audit of the parliamentary election outcome. Our example is the New South Wales Legislative Council election of 2015, but the same process could be used for any similar parliament for which data was available, such as the Australian House of Representatives given the proposed automatic scanning of ballots

Kinetic, Spectroscopic, and X-Ray Crystallographic Evidence for the Cooperative Mechanism of the Hydration of Nitriles Catalyzed by a Tetranuclear Ruthenium-μ-oxo-μ-hydroxo Complex

The tetranuclear ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was found to be a highly cooperative catalyst for the nitrile hydration reaction. The cooperative mechanism of the hydration of benzonitrile was established by Hill inhibition kinetics. The treatment of a nitrile substrate with complex 1 led to the catalytically relevant nitrile-coordinated tetraruthenium complex 3. The X-ray structure of the nitrile-coordinated complex 3 showed a considerably “relaxed” tetrameric core structure compared to that of 1. The hydration of para-substituted benzonitriles p-X-C6H4CN with an electron-withdrawing group (X = Cl, Br, CO2H, CF3) exhibited cooperative kinetics, as indicated by the sigmoidal saturation kinetics, while the hydration of nitriles with an electron-donating group (X = OH, OMe, t-Bu, CH3) obeyed Michaelis–Menten saturation kinetics. The formation of a ruthenium hydride species was observed during the hydration of methacrylonitrile, and its monomeric nature was established by using DOSY NMR techniques

Isomer Dependence in the Assembly and Lability of Silver(I) Trifluoromethanesulfonate Complexes of the Heteroditopic Ligands, 2-, 3-, and 4-[Di(1\u3cem\u3eH\u3c/em\u3e-pyrazolyl)methyl]phenyl(di-\u3cem\u3ep\u3c/em\u3e-tolyl)phosphine

Three isomers of a new heteroditopic ligand that contains a di(1H-pyrazolyl)methyl (−CHpz2) moiety connected to a di(p-tolyl)phosphine group via a para-, meta-, or ortho-phenylene spacer (pL, mL, and oL, respectively) have been synthesized by using a palladium(0)-catalyzed coupling reaction between HP(p-tolyl)2 and the appropriate isomer of (IC6H4)CHpz2. The 1:1 complexes of silver(I) trifluoromethanesulfonate, Ag(OTf), were prepared to examine the nature of ligand coordination and the type of supramolecular isomer (monomeric, cyclic oligomeric, or polymeric) that would be obtained. The single crystal X-ray diffraction studies showed that [Ag(pL)](OTf), 1, and [Ag(mL)](OTf), 2, possessed cyclic dimeric dications, whereas [Ag(oL)](OTf), 3, was a coordination polymer. The polymeric chain in 3 could be disrupted by reaction with triphenylphosphine, and the resulting complex, [Ag(oL)(PPh3)](OTf), 4, possessed a monometallic cation where the ligand was bound to silver in a chelating κ2P,N- coordination mode. The solution structures of 1–4 were probed via a combination of IR, variable-temperature multinuclear (1H, 13C, 31P) NMR spectroscopy, as well as by electron spray ionization (ESI)(+) mass spectrometry. A related complex [Ag(m-IC6H4CHpz2)2](OTf), 5, was also prepared, and its solid-state and solution spectroscopic properties were studied for comparison purposes. These studies suggest that the cyclic structures of 1 and 2 are likely preserved but are dynamic in solution at room temperature. Moreover, both 3 and 4 have dynamic solution structures where 3 is likely extensively dissociated in CH3CN or acetone rather than being polymeric as in the solid state

Charge-Transfer Bonding in Metal–Arene Coordination

X-ray crystallographic structures of donor–acceptor complexes of aromatic hydrocarbons with transition metals are re-examined with the focus on the arene ligands. Thus, significant structural and electronic changes are revealed in the arene moiety due to coordination to the metal center including: (i) expansion of the aromatic six-carbon ring; (ii) endocyclic π-bond localization; (iii) distortion of the planarity (folding) of the arene ring; and (iv) shortening of the metal-arene bond distances. All structural features are characteristic of metal–arene (π- or σ-) complexes that exhibit various degrees of (metal-to-ligand) charge transfer. The concept of charge-transfer bonding not only explains the structural details but also the various facets of chemical reactivity of metal-coordinated arenes including efficient carbon-hydrogen bond activation and nucleophilic–electrophilic umpolung, both of which are critical factors in homogeneous metal catalysis

Photoinduced Coupling of Acetylenes and Quinone in the Solid State as Preorganized Donor−Acceptor Pairs

Crystalline electron donor−acceptor (EDA) complexes of various diarylacetylenes (DA) and dichlorobenzoquinone (DB) are isolated and structurally characterized by X-ray crystallography. Deliberate excitation of either the DB acceptor at λDB = 355 nm or the 1:2 [DA, 2DB] complex at λCT = 532 nm in the solid state leads to [2 + 2] cycloaddition and identical (isomeric) mixtures of the quinone methide products. Time-resolved (ps) diffuse reflectance spectroscopy identifies the ion-radical pair [DA•+, DB•-] as the reactive intermediate derived by photoinduced electron transfer in both photochemical procedures. The effects of crystal-lattice control on the subsequent ion-radical pair dynamics are discussed in comparison with the same photocouplings of acetylenes and quinone previously carried out in solution

Preparation and Structures of Crystalline Aromatic Cation-Radical Salts. Triethyloxonium Hexachloroantimonate as a Novel (One-Electron) Oxidant

Triethyloxonium hexachloroantimonate [Et3O+SbCl6-] is a selective oxidant of aromatic donors (ArH), and it allows the facile preparation and isolation of crystalline paramagnetic salts [ArH+•, SbCl6-] for the X-ray structure determination of various aromatic cation radicals. The mechanistic relationship between the Meerwein salt [Et3O+SbCl6-] and the pure Lewis acid oxidant SbCl5 is based on a prior ethyl transfer from oxygen to chlorine within the ion pair

Novel Synthesis and Structures of Tris-Annelated Benzene Donors for the Electron-Density Elucidation of the Classical Mills−Nixon Effect

A versatile method for the high-yield synthesis of various tris-, bis-, and mono-annelated benzenes (as well as cyclooctatetraene) is based on the Pd-catalyzed coupling of three (or four) ethylenic units comprised of α,β-dibromoalkenes and α‘-alkenyl Grignard reagentsall carried out in a single pot. The particular application to tris(bicyclopentyl)-annelated benzene yields the syn isomer 1s in high purity; X-ray diffraction analysis confirms the aromatic bond alternation relevant to the Mills−Nixon effect. Most importantly, the efficient synthesis of 1s crystals of extraordinary quality allows us (for the first time) to make precise electron-density measurements of the “banana-type” distortion and the ellipticity (π-character) of the various aromatic C−C bondssufficient to identify the electronic origin of the classical Mills−Nixon effect. The unique electron-donor properties of tris-annelated benzenes also relate to their highly reversible one-electron oxidation potentials even in nonpolar solvents

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

The stepwise (one-electron) chemical oxidation of the tetraphenylethylene donor and its substituted analogues (D) can be carried out by electron exchange with aromatic cations or antimony(V) oxidants to selectively afford the cation radical (D+•) initially and then the dication (D2+). The ready interchange of the latter establishes the facile disproportionation (i.e., 2D+• ⇌ D2+ + D) that was originally examined by only transient electrochemical techniques. The successful isolations of the crystalline salts of the tetraanisylethylene cation radical (1+•) as well as the tetraanisylethylene dication (12+) allow X-ray diffraction analysis (for the first time) to quantify the serial changes in the molecular structure upon successive oxidations. Five structural parameters (d, l, θ, φ, and q) are identified as quantitative measures of changes in bond (CαCβ, Cαanisyl) lengths, dihedral (CαCβ)/torsional (anisyl) angles, and quinoidal (anisyl) distortion attendant upon the removal of first one-electron and then another electron from the tetraanisylethylene framework. The linear variation of all five parameters in Chart 3 point to a strongly coupled relaxation of tetraanisylethylene (involving simultaneous changes of d, l, θ, φ, and q) to a severely twisted dication. Most noteworthy is the structure of the cation radical 1+• with d, l, θ, φ, and q values that are exactly one-half those of the dication. The complex molecular changes accompanying the transformation:  D → D+• → D2+ bear directly on the donor properties and the disproportionation processes of various tetraarylethylenes

Isolation and X-ray Structures of Labile Benzoic- and Acetic-Acidium Carbocations

New carbocationic salts (via O-protonation of substituted benzoic acids) are prepared for the first time by controlled hydration of the corresponding benzoylium salts and isolated in pure crystalline form. Precise X-ray structural analyses reveal the rather unexpected (electronic) structure of the carboxylic-acidium functionality

Isolation, X-ray Structures, and Electronic Spectra of Reactive Intermediates in Friedel−Crafts Acylations

Reactive intermediates in the Friedel−Crafts acylation of aromatic donors are scrutinized upon their successful isolation and X-ray crystallography at very low temperatures. Detailed analyses of the X-ray parameters for the [1:1] complexes of different aliphatic and aromatic-acid chlorides with the Lewis acids antimony pentafluoride and pentachloride, gallium trichloride, titanium and zirconium tetrachlorides provide unexpected insight into the activation mechanism for the formation of the critical acylium carbocations. Likewise, the X-ray-structure examinations of aliphatic and aromatic acylium electrophiles also isolated as crystalline salts point to the origins of their electrophilic reactivity. Although the Wheland intermediates (as acylium adducts to arene donors) could not be isolated in crystalline form owing to their exceedingly short lifetimes, transient (UV−vis) spectra of benzenium adducts of acylium carbocations with hexamethylbenzene can be measured and directly related to Wheland intermediates with other cationic electrophiles that have been structurally established via X-ray studies