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PhIBrsub2/sub, first purported to exist over 100 years ago, has been subject of few reports due to its low stability. However, a recent publication proposes a reaction of PIFA (PhI(OC(O)-CFsub3/sub)sub2/sub) with TMSBr to form PhIBrsub2/subiin situ/iand demonstrated its efficacy in aryl brominations. This report investigates this synthesis by replicating bromination reactions claiming to useiin situ/iPhIBrsub2/subas described. The spectroscopical and computational results indicate formation of PhI and Brsub2/subwhere Brsub2/subis responsible for bromination and no supporting evidence for invoking PhIBrsub2/subas an intermediate is found.

It has been previously proposed that pyridines can activate PhICl2 by displacing a chloride and forming the [PhI(Pyr)(Cl)]+ cation as a reactive intermediate. Here we show that pyridine does not displace chloride, but rather forms a weak complex with the iodine via halogen bonding along the C-I bond axis. This interaction is interrogated by NMR, structural, charge density, and theoretical investigations, which all indicate that pyridine does not activate PhICl2 as proposed.

A study on the potential activating role of pyridine in the electrophilic chlorination of anisole by PhICl2 has led to the discovery that soluble sources of chloride ions activate PhICl2 in the reaction at catalytic loadings, greatly increasing the rate of chlorination. It is further shown that presence of chloride increases the rate of decomposition of PhICl2 into PhI and Cl2. The specific mechanism by which chloride induces electrophilic chlorination and decomposition of PhICl2 remains an open question.

The mono- and dianions of CO2 (i.e., CO2− and CO22−) have been studied for decades as both fundamentally important oxycarbanions (anions containing only C and O atoms) and as critical species in CO2 reduction and fixation chemistry. However, CO2 anions are highly unstable and difficult to study. As such, examples of stable compounds containing these ions are extremely limited; the unadulterated alkali salts of CO2 (i.e., MCO2, M2CO2, M = alkali metal) decompose rapidly above 15 K, for example. Herein we report the chemical reduction of a cyclic (alkyl)(amino) carbene (CAAC) adduct of CO2 at room temperature by alkali metals, which results in the formation of CAAC-stabilized alkali CO2− and CO22− clusters. One-electron reduction of CAAC–CO2 adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals [M(CAAC–CO2)]n (M = Li, Na, K, 2–4) analogous to the alkali CO2− radical, and two-electron alkali metal reduction affords dianionic clusters of the general formula [M2(CAAC–CO2)]n (5–8) with reduced CO2 units which are structurally analogous to the carbonite anion CO22−. It is notable that crystalline clusters of these alkali–CO2 salts may also be isolated via the “one-pot” reaction of free CO2 with free CAAC followed by the addition of alkali metals – a process which does not occur in the absence of carbene. Each of the products 2–8 was investigated using a combination of experimental and theoretical methods.

ion of a pyridine ligand from Weiss’ reagent ([PhI(Pyr)2]2+) using BF3-Et2O was found to activate Weiss’ reagent towards electrophilic aromatic substitution reactions. The activated species can be isolated when 4-DMAP is used as the pyridine ligand and was determined to be [PhI(4-DMAP)]2+ in solution. The isolated cation was reactive in electrophilic aromatic substitution reactions towards mesitylene, xylene and toluene that Weiss’ reagent itself does not react with.

A family of four Ir(iii) complexes of the form [Ir(ppy)2(L)]Cl (where ppy = 2-phenyl-pyridine and L = a pyridyl-1,2,4-triazole or pyridyl-1,3,4-oxadiazole ligand bearing a boronic acid group) have been prepared as potential luminescent sensors for carbohydrates. A modular eight step procedure was developed to synthesise the complexes, and this was initiated with the preparation of two benzhydrazide and three S-ethylated pyridine-2-thiocarboxamides precursors. Reaction of these precursors produced three new 1,2,4-triazole- and one 1,3,4-oxadiazole-based ligands substituted with boronic acid pinacol ester groups. The boronic acid pinacol esters were then converted to boronic acids in two steps via potassium trifluoroborate intermediates. The boronic acid substituted ligands and their Ir(iii) complexes were fully characterised using a range of techniques including X-ray crystallography in the case of the pyridyl-1,3,4-oxadiazole ligand and two of the Ir(iii) complexes. The capacity of the synthesised Ir(iii) complexes to form boronic acid cyclic esters with the simple sugars glucose and fructose was evaluated using high-resolution mass spectrometry (HRMS) and photoluminescence titration studies. These studies confirm that the Ir(iii) complexes form adducts with both glucose and fructose, with increased levels of boronic acid cyclic esters being formed with fructose at higher pHs. Theoretical calculations were used to gain insight into the nature of the electronic transitions involved in the electronic absorption and emission spectra.

A new strategy to create iridium(iii)-based ECL labels reveals limitations of conventional approaches., Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

Previously reported annihilation ECL of mixtures of metal complexes have generally comprised Ir(ppy)3 or a close analogue as a higher energy donor/emitter (green/blue light) and [Ru(bpy)3]2+ or its derivative as a lower energy acceptor/emitter (red light). In contrast, here we examine Ir(ppy)3 as the lower energy acceptor/emitter, by combining it with a second Ir(iii) complex: [Ir(df-ppy)2(ptb)]+ (where ptb = 1-benzyl-1,2,3-triazol-4-ylpyridine). The application of potentials sufficient to attain the first single-electron oxidation and reduction products can be exploited to detect Ir(ppy)3 at orders of magnitude lower concentration, or enhance its maximum emission intensity at high concentration far beyond that achievable through conventional annihilation ECL of Ir(ppy)3 involving comproportionation. Moreover, under certain conditions, the colour of the emission can be selected through the applied electrochemical potentials. We have also prepared a novel Ir(iii) complex with a sufficiently low reduction potential that the reaction between its reduced form and Ir(ppy)3+ cannot populate the excited state of either luminophore. This enabled, for the first time, the exclusive formation of either excited state through the application of higher cathodic or anodic potentials, but in both cases, the ECL was greatly diminished by parasitic dark reactions.

The electronic spectra of 2-bromoethylbenzene and its chloro and fluoro analogues have been recorded by resonant two-photon ionisation (R2PI) spectroscopy. Anti and gauche conformers have been assigned by rotational band contour analysis and IR-UV ion depletion spectroscopy in the CH region. Hydrate clusters of the anti conformers have also been observed, allowing the role of halocarbons as hydrogen bond acceptors to be examined in this context. The donor OH stretch of water bound to chlorine is red-shifted by 36 cm−1, or 39 cm−1 in the case of bromine. Although classed as weak H-bond acceptors, halocarbons are favourable acceptor sites compared to π systems. Fluorine stands out as the weakest H-bond acceptor amongst the halogens. Chlorine and bromine are also weak H-bond acceptors, but allow for more geometric lability, facilitating complimentary secondary interactions within the host molecule. Ab initio and DFT quantum chemical calculations, both harmonic and anharmonic, aid the structural assignments and analysis.

We have carried out a theoretical investigation of benzene substituted with BeO to assess stability and aromatic properties (with 1-3 BeO units in a six-membered ring); C4H4BeO, C2H2Be2O2, and Be3O3. All species retain a planar geometry. We considered both bare complexes and Be coordinated with L = CO, pyridine, PMe3, and NHC. Coordination of a ligand to Be atoms causes increased Be-O bond distances. Aromatic character has been investigated with NICS and NICS-scan calculations, EDA analysis, as well as considering the energetics of hydrogenation. The complexes with the greatest aromatic character are C4H4BeO (3), and C4H4Be(CO), which have negative NICS(1)zz values and minima in the NICS-scan. Coordination of two ligands to make the Be four-coordinate disrupts ring planarity and reduces aromatic character.

Reaction of phenylsilane with the ring expanded carbene 6-Mes results in facile Si-H oxidative addition to the carbenic carbon at room temperature. Heating the resultant diorganosilane product induces ring expansion through silicon to carbon migration of either the Si-H or Si-Ph bonds.

The reactions of molecules containing E-H functionalities (E = Group 15 or 16 element) and pentaphenylborole were investigated revealing diverse outcomes. For aniline and water, protodeborylation ring opening reactions occurred via the N-H or O-H bonds. Pentaphenylborole reacted with water in a 1 : 1 or 2 : 1 ratio to yield the corresponding boroxane and diboroxane, respectively, whereas aniline reacted strictly in a 1 : 1 ratio. Interestingly, 1-naphthalenethiol reacted to produce a 1-bora-cyclopent-3-ene heterocycle. The reaction with a primary phosphine generated an adduct which was resilient, even at elevated temperatures. DFT calculations provide support for the observed reaction products, and identify the initial adduct as a key intermediate in determining the final product. In particular, ring opening may be linked to the lability of the hydrogen in the initial adduct. Collectively, these reactions provide insight into new reaction pathways, the stability of boroles, as well as mechanistic insight into previously reported transformations.

The formation of a new class of I(III) compound is reported; an N,N′ chelated iodine cation ([bpy-ICl2]+; bpy = 2,2′-bipyridine). The complex is obtained as an [ICl4]− salt and is formed via simple reaction of bpy with ICl3. The compound is relatively unstable, but may be stored as a solid and is shown to be competent in the oxidative chlorination of Au(I)-NHC complexes.

Four cationic heteroleptic iridium(III) complexes have been prepared from methyl- or benzyl-substituted chelating imidazolylidene or benzimidazolylidene ligands using a Ag(I) transmetallation protocol. The synthesised iridium(III) complexes were characterised by elemental analysis, ᴵH and ᶦᶟC NMR spectroscopy and the molecular structures for three complexes were determined by single crystal X-ray diffraction. A combined theoretical and experimental investigation into the spectroscopic and electrochemical properties of the series was performed in order to gain understanding into the factors influencing photoluminescence and electrochemiluminescence efficiency for these complexes, with the results compared with those of similar NHC complexes of iridium and ruthenium. The N^C coordination mode in these complexes is thought to stabilise thermally accessible non-emissive states relative to the case with analogous complexes with C^C coordinated NHC ligands, resulting in low quantum yields. As a result of this and the instability of the oxidised and reduced forms of the complexes, the electrogenerated chemiluminescence intensities for the compounds are also low, despite favourable energetics. These studies provide valuable insights into the factors that must be considered when designing new NHC-based luminescent complexes. Refereed/Peer-reviewed

N-heterocyclic carbenes (NHCs) are generally considered to be extremely robust, ideal spectator ligands. However, in the past two years there have been several reports of the activation of the endocyclic C-N bond with subsequent insertion into element-hydrogen and element-carbon bonds. The new reaction pathway casts the reactivity of the NHC heterocyclic ring into a new light, especially in the context of potential catalyst decomposition. The synthetic reports and theoretical studies in this rapidly developing area are summarized here.

The reaction between trimethylsilyl azide and pentaphenylborole was recently shown to produce the corresponding 1,2-azaborine. Investigating this transformation theoretically suggests that the reaction proceeds via coordination of the azide to the borole, rearrangement to a bicyclic species, and conversion to a kinetically favoured eight-membered BN3C4 heterocycle or expulsion of N2 to furnish the thermodynamically favoured 1,2-azaborine. The eight-membered species was structurally characterized as a borole adduct and represents an unusual analogue of cyclooctatetraene.

Ab initio metods have been employed to investigate first row transition metal hydrides and helides of form: TMHn+ (where n = 0–2) and TMHen+ (where n = 1–3), respectively. Multi-configurational SCF and IC-MRCI methods have been used, along with all-electron ROHF-UCCSD(T) methods, in order to compare trends in the bonding of these series. Equilibrium geometries, dissociation energies and vibrational frequencies have been determined for the low-lying electronic states. A comparison with the diatomic first row transition metal hydrides illustrates the limit of isoelectronic approaches and so further highlights the unique binding properties of helium.

The all-electron CCSD(T)/cc-pCVTZ level of theory was used to generate a 63 point discrete potential energy hypersurface for the χ 2A1 electronic state of He2C3+. The optimized geometry was of C2v symmetry with a RC–He bond length of 1.218 Aand an included bond angle of 107.9°. Dissociation products were also examined. A Pade′ (4,5) potential function, employing a Simons–Parr–Finlan expansion variable, was used in subsequent calculations. The fit to the discrete abinitio surface yielded a (χ2)1/2 value of 1.35×10-5Eh. The potential function was embedded in an Eckart–Watson rovibrational Hamiltonian, which was solved variationally. The '‘full’' anharmonic fundamental frequencies for the breathe, bend and asymmetric stretch vibrations were 1199.2, 673.4 and 1411.9 cm-1 respectively. Vibrational intensities were calculated using the variational wavefunctions and a dipole moment function generated from an all-electron QCISD/aug-cc-pVTZ 43 point dipole moment surface.

A theoretical study focusing on the ring expansion that occurs in the reaction of N-heterocyclic carbenes with silanes has been carried out. A detailed reaction pathway was determined which indicates that formation of C-H bonds is the crucial factor in the transformation.

The ground state potential energy surfaces (PESs) of MH(2)(n+) (M = Li, Be, Na, Mg, K, Ca; n = 1, 2) have been investigated using relativistically corrected, coupled-cluster (CC) and multi-reference configuration interaction (MRCI) methods. The PESs for MH(2)(+) (M = Li, Na, K) and MH(2)(n+) (M = Be, Mg, Ca; n = 1, 2) exhibit global minima corresponding to C(2v) symmetry equilibrium structures, with local minima for D(∞h) and C(∞v) symmetry states. Conversely, the ground state PESs of LiH(2)(2+), NaH(2)(2+) and KH(2)(2+) are repulsive. In all cases, the D(∞h) states resulting from the insertion of M(n+) into the H(2) moiety were significantly higher in energy than the co-linear C(2v) states. It is generally assumed a priori that these species are the result of the interaction between the metal ion charge state and the quadrupole moment of the H(2) moiety. However, analysis of the functional ΔΘ(αα)(R(M(n+)-H(2))) = Θ(αα)(MH(2)(n+)) - Θ(αα)(M(n+)) (which is effectively the difference between traceless quadrupole moments (Θ(αα)) of MH(2)(n+) and the isolated M(n+) ion computed using MRCI) as a function of M(n+)-H(2) distance demonstrates that a local maximum in ΔΘ(αα) along the molecular C(2) axis is necessary for the formation of a thermodynamically stable complex. It is concluded that the topology of ΔΘ(αα) provides a convenient indicator of the stability of such molecular ion-quadrupole complexes.

Multi-reference configuration interaction (MRCI) calculations have been employed to characterize the low-lying states of first-row transition metal dihelide dications, He(2)TM(2+) (TM = Sc-Cu). The most important state-ordering principles were determined to be the occupation of the 4s orbital and orientation of the occupied 3d orbital. The ground states of all species are predicted to be of D(infinityh) symmetry arising from a 3d(n+1) electronic configuration. For excited states with singly occupied 4s or doubly occupied 3d(sigma) orbitals, bending to C(2v) symmetry typically lowers the energy and shortens the He-TM bond length. Coupled cluster singles and doubles with a perturbative treatment of triple excitations (CCSD(T)) results for ground state spectroscopic properties are in agreement with the MRCI predicted trends.