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This report investigates the fundamental basis for rather surprising patterns of reactivity in Bronsted acid-mediated cyclizations of pyrrole substrates bearing pendant Michael acceptors that were identified during syntheses of Stemona alkaloids. Integrated experimental and theoretical studies reveal the profound influence that substituent effects have on the viability of these transformations. Additionally, we identify that electronic effects, in addition to barrier-lowering secondary orbital interactions within transition states, account for the exclusive preference for 7-endo-trig cyclizations over 6-exo-trig cyclizations.

The octol of a new rigid, tetraarylene-bridged cavitand was investigated for self-assembly behaviour in solution. 1H and DOSY NMR spectroscopic experiments show that the cavitand readily dimerizes through an unusual seam of interdigitated hydrogen-bonds that is resistant to disruption by polar co-solvents. The well-defined cavity encapsulates small cationic guests, but not their neutral counterparts, restricting the conformation of sequestered tetraethylammonium in solution and the solid state., A robust, dimeric capsule forms quantitatively in low-polarity solvents via a seam of 8 hydrogen bonds. The resulting electron-rich cavity selectively binds small organic cations over neutral counterparts.

Palladium(II) boronates are recognized as fundamental pre-transmetalation intermediates in Suzuki-Miyaura cross-couplings. While these typically transient species have been detected and studied spectroscopically, it is conspicuous that they have never been isolated since this important reaction was discovered over forty years ago. This study reports the synthesis of a family of unprecedented arylpalladium(II) boronates that are, by design, kinetically stable at ambient temperature, both in solution and in the solid state. These properties enabled unambiguous crystallographic confirmation of their structure for the first time and their chemical competence in a Suzuki-Miyaura reaction was demonstrated.

This study investigates the mechanism of Suzuki-Miyaura Csp2-Csp2 cross-couplings facilitated by PCP-type nickel(II) pincer complexes. By employing a combination of standard experimental and theoretical methods, it is proposed that a nickel(I)/(III) cycle is involved in this reaction and single-electron pathways likely operate in this transformation.

The three-component reaction between a resorcinol, 1,3-dimethoxybenzene, and an alkyl aldehyde (R = C1-C11) along with BF3·OEt2 affords a C2v-symmetric resorcin[4]arene tetraether in one step; in most cases, the single isomer can be precipitated from the reaction mixture in moderate to excellent yields (up to 89%). The reaction is tolerant of 2-substituted resorcinols (R' = OH, Cl, Br, Me), allowing a third type of functionality to be regioselectively incorporated during the macrocyclization.

The first total syntheses of the Stemona alkaloid dehydrostenine A and the structure assigned to dehydrostenine B have been completed from a simple pyrrole substrate in 10 and 11 steps, respectively. Two independent Bronsted-acid-mediated intramolecular Michael additions were exploited to construct the tetracyclic dehydrostenine core. As a result of synthetic studies and associated analysis of the relevant literature, revisions of the structures originally assigned to dehydrostenines A and B are proposed.

We have identified and extensively investigated the photochemical activation and reaction of a hydroxyquinone-derived phenyliodonium ylide in the presence of visible light using experiment and theory. These studies revealed that in its photoexcited state this iodonium is capable of facilitating a range of single-electron transfer (SET) processes, including hydrogen atom transfer (HAT), a Povarov-type reaction, and atom-transfer radical addition chemistry. Where possible, we have employed density functional theory (DFT) to develop a more complete understanding of these photoinduced synthetic transformations.

A series of electron donor–acceptor compounds are reported in which both the donor and acceptor strengths are systematically altered using mono-, bi-, and terthiophene as donors and benzo[c][1,2,5]...

The three-component reaction between a resorcinol, 1,3-dimethoxybenzene, and an alkyl aldehyde (R = C

The ground and excited state photophysical properties of a series of fac-[Re(L)(CO)3(α-diimine)]n+ complexes, where L = Br–, Cl–, 4-dimethylaminopyridine (dmap) and pyridine (py) have been extensively studied utilizing numerous electronic and vibrational spectroscopic techniques in conjunction with a suite of quantum chemical methods. The α-diimine ligand consists of 1,10-phenanthroline with the highly electron donating triphenylamine (TPA) appended in the 5 position. This gives rise to intraligand charge transfer (ILCT) states lying lower in energy than the conventional metal-to-ligand charge transfer (MLCT) state, the energies of which are red and blue-shifted, respectively, as the ancillary ligand, L becomes more electron withdrawing. The emitting state is 3ILCT in nature for all complexes studied, characterized through transient absorption and emission, transient resonance Raman (TR2), time-resolved infrared (TRIR) spectroscopy and TDDFT calculations. Systematic modulation of the ancillary ligand caus...

One of a number of intriguing new alkaloids isolated from the Leucetta sp. sponge in 2004, spiroleucettadine displayed unique structural features on a restricted scaffold: a trans-fused 5,5-bicyclic ring system together with an amino hemiketal moiety. Attempts to synthesize the initially proposed structure failed, raising questions as to its veracity, and structure revision ensued in 2008; no successful synthetic approach has been reported to date. Herein, we describe the enantiospecific total synthesis of (-)-spiroleucettadine by a highly efficient biomimetic approach starting from l-tyrosine. One of two key hypervalent-iodine-mediated oxidation reactions forged the spirocyclic center, and the other enabled the installation of the methylamine side chain in the penultimate step. Our approach provides synthetic access to a new class of spiroannulated natural products and will enable future studies of the structure-biological-activity relationships of these antibacterial compounds.

Four planar tripyridyl ligands (Ltripy), 1,3,5-tris(pyridin-3-ylethynyl)benzene 1 a, 1,3,5-tris[4-(3-pyridyl)phenyl]benzene 2 a, and the hexyloxy chain functionalized derivatives 1,3,5-tris[(3-hexyloxy-5-pyridyl)ethynyl]benzene 1 b, and 1,3,5-tris[4-(3-hexyloxy-5-pyridyl)phenyl]benzene 2 b, were synthesized and used to generate a family of [Pd6(Ltripy)8](BF4)12 octahedral cages (Ltripy=1 a, b or 2 a, b). The ligands and cages were characterized using a combination of 1H, 13C, and DOSY nuclear magnetic resonance (NMR) spectroscopy, high resolution electrospray mass spectrometry (HR-ESI-MS), infrared (IR) spectroscopy, elemental analysis, and in three cases, X-ray crystallography. The molecular recognition properties of the cages with neutral and anionic guests were examined, in dimethyl sulfoxide (DMSO), using NMR spectroscopy, mass spectrometry and molecular modeling. No binding was observed with simple aliphatic and aromatic guest molecules. However, anionic sulfonates were found to interact with the octahedral cages and the binding interaction was size selective. The smaller [Pd6(1 a, b)8]12+ cages were able to interact with three p-toluenesulfonate guest molecules while the larger [Pd6(2 a, b)8]12+ systems could host four of the anionic guest molecules. To probe the importance of the hydrophobic effect, a mixed water–DMSO (1:1) solvent system was used to reexamine the binding of the neutral organic guests adamantane, anthracene, pyrene and 1,8-naphthalimide within the cages. In this solvent system all the guests except adamantane were observed to bind within the cavities of the cages. NMR spectroscopy and molecular modeling indicated that the cages bind multiple copies of the individual guests (between 3–6 guest molecules per cage).

We report herein the synthesis and optical properties of unsymmetrically substituted hexaazatrinaphthalene (HATN) systems, and the influence of donor additivity on the electronic properties of the material. The hexaazatrinaphthalenes have been studied by means of electrochemical, electronic absorption and emission, FT Raman and resonance Raman methodologies coupled with DFT calculations. The optical spectra are dominated by low-energy charge-transfer states, which show a redshift of excitation energy of around 0.1 eV and an increase in e of around 125 % as the number of donors is increased. The emission spectra exhibit significant solvatochromism, with Lippert–Mataga analysis yielding Δµ values between 34 and 60 D.

A transition-metal-based donor-(linker)-acceptor system can produce long-lived charge transfer excited states using visible excitation wavelengths. The ground- and excited-state photophysical properties of a series of [ReCl(CO)

A rapid and facile synthesis of benzannulated 6,5-spiroketals from vinyl 1,1-diacylcyclopropanes is reported. The method utilizes mild reaction conditions with good to excellent yields and high diastereoselectivity. This methodology was then used to construct the core of berkelic acid.

A new method to access benzannulated spiroketals from 1,1-diacyl phenylcyclopropanes is described. The method provides rapid access to 5,5 and 5,6-benzannulated spiroketals in low to moderate yields and with moderate to good diastereoselectivity.

A series of Ru(II) 2,2′-bipyridine (bpy) complexes with an electron-accepting dipyrido[3,2-a:2′,3′-c]phenazine (dppz) ligand coupled to an electron-donating triarylamine (TAA) group have been investigated. Systematic alteration of a bridging unit between the dppz and TAA allowed exploration into how communication between the donor and acceptor is perturbed by distance, as well as by steric and electronic effects. The effect of the bridging group on the electronic properties of the systems was characterized using a variety of spectroscopic methods, including Fourier transform–Raman (FT-Raman) spectroscopy, resonance Raman spectroscopy, and transient resonance Raman (TR2) spectroscopy. These methods were used in conjunction with ground- and excited-state absorption spectroscopy, electrochemical studies, and DFT calculations. The ground-state electronic absorption spectra show distinct variation with the bridging group, with the wavelength observed for the lowest energy electronic transition ranging from 449...

A series of donor-acceptor compounds is reported in which the energy of the triarylamine donor is systematically tuned through para substitution with electron-donating methoxy and electron-withdrawing cyano groups. The acceptor units investigated are benzothiadiazole (btd), dipyridophenazine (dppz), and its [ReCl(CO)3(dppz)] complex. The effect of modulating donor energy on the electronic and photophysical properties is investigated using (1)H NMR spectroscopy, DFT calculations, electrochemistry, electronic absorption and emission spectroscopies, ground state and resonance Raman spectroscopy, and transient absorption spectroscopy. Qualitative correlations between the donor energy and the properties of interest are obtained using Hammett σ(+) constants. Methoxy and cyano groups are shown to destabilize and stabilize, respectively, the frontier molecular orbitals, with the HOMO affected more significantly than the LUMO, narrowing the HOMO-LUMO band gap as the substituent becomes more electron-donating-observable as a bathochromic shift in low-energy charge-transfer absorption bands. Charge-transfer emission bands are also dependent on the electron-donating/withdrawing nature of the substituent, and in combination with the highly solvatochromic nature of charge-transfer states, emission can be tuned to span the entire visible region.

Nonporous coordination polymers (CPs) constructed from flexible bridging ligands have seldom been utilized in practical applications, owing to limited solubility and/or stability in most solvents. Here we have produced nanocrystal coordination polymers (NCPs) with identical crystalline structure to their macroscale counterparts, high solvent dispersibility, and large effective surface area for catalytic application. A microemulsion system has been developed for the mild synthesis of the ZnII- and CuII-NCPs, resulting in control over the size, morphology, and reactivity. Both ZnII- and CuII-NCPs demonstrated high catalytic activity in a ring opening reaction of cyclohexene oxide with aniline; furthermore, reduced Cu-NCPs were employed as efficient, reusable catalysts for an azide–alkyne cycloaddition “click” reaction in the nonpolar solvent heptane. In contrast, all macroscale CP equivalents, prepared by conventional methods, were catalytically inactive.

The synthesis of two bipyridine-hexa-peri-hexabenzocoronene (bpy-HBC) ligands functionalized with either (t)Bu or C12H25 and their Re(I) tricarbonyl chloride complexes are reported and their electronic properties investigated using spectroscopic and computational methods. The metal complexes show unusual properties, and we observed the formation of a long-lived excited state using time-resolved infrared spectroscopy. Depending on the solvent, this appears to be of the form Rebpy(•-)HBC(•+) or a bpy-centered π,π* state. TD-DFT calculations support the donor-acceptor charge transfer character of these systems, in which HBC is the donor and bpy is the acceptor. The ground state optical properties are dominated by the HBC chromophore with additional distinct transitions of the complexes, one associated with MLCT 450 nm (ε17 000 L mol(-1) cm(-1)) and another with a HBC/metal to bpy charge transfer, termed the MLLCT band (373 nm, ε = 66 000 L mol(-1) cm(-1)). These assignments are also supported by resonance Raman spectroscopy.

Brefeldin A (BFA) is a fungal metabolite that displays a wide range of biological activities making it an attractive target for drug discovery. To explore the biological potential of the BFA scaffold an amine-macrocycle target 3 was proposed. To access, we dissembled BFA into smaller building blocks in preparation for regenerating the macro-lactone. These entities can then be used to synthesise new brefeldin analogues with various new structural features for biological testing. To overcome supply issues a scaled fermentation process of Penicillium camemberti was employed generating 4.5 kg of BFA. Novel N-BFA type derivatives were generated and herein we describe the synthesis of two new scaffolds 12 and 14 from BFA over six steps in 24% and 17% yield, respectively. A trans-fused bicyclic cyclopentanoid piperidine scaffold 16 can be generated from 12 that may serve as a valuable new scaffold for the synthesis of novel natural product-like compounds.

Hexa-peri-hexabenzocoronenes with a bay-fused five-membered ring are synthesized from fluorenyl precursors. The key oxidative cyclodehydrogenation step is accompanied by regioselective chlorination that is enhanced by methylation at the cyclopenta-ring or increased reaction concentration. The CpHBC products undergo mild electrophilic aromatic bromination, without catalyst, to afford adducts suitable for π-extension by cross-coupling.

The synthesis, spectroscopic characterization, and computational modeling of seven benzo[c][2,1,3]thiadiazole-based donor–acceptor dyes is reported. Using a range of linker units, it is possible to alter the lowest energy transition in terms of intensity (from 8000 to 25000 L mol–1 cm–1) and wavelength (from 350 to 430 nm). Resonance Raman spectroscopy was used in concert with DFT calculations to indicate that the linker unit participates in charge transfer processes. In each compound the excited state behavior appears to be primarily described by a BTD●–-Linker-TPA●+ state. Stokes shift versus solvent parameter gradients are on the order of 15000 cm–1, indicating Δμ values are large. Dual emission is observed in six of the seven compounds and it can be modulated as a function of solvent. TD-DFT calculations, including excited state optimizations (linear response and state specific), indicate that the lowest energy emission is charge transfer in character. The high energy emissive state is assigned as n−π...

Various strategies toward the synthesis of the marine natural product (−)-spiroleucettadine are described. In the original strategy, a biomimetic inspired oxidation of a 2-imidazoline scaffold uncovered unexpected reactivity, where benzylic oxidation followed by a Baeyer–Villiger reaction was observed. The second generation approach examined oxidative dearomatization of the phenol ring system first, where a competing spirocyclization process was uncovered. Efforts to forge the scaffold via a carbocation mediated benzyl migration were unsuccessful. Highlights of the successful synthesis include two consecutive hypervalent iodine reactions: the first formed the spirocyclic center and the second facilitated installation of an acetate group at the C-5 position to allow for subsequent introduction of the methyl amine side chain.

Container molecules (cavitands) derived from resorcin[4]arene are of broad interest in supramolecular chemistry as hosts and fragments of larger constructs. Herein is presented a new class of rigid cavitand where the resorcin[4]arene carbon framework is extended with four bridging arylene rings. Two tenable, isomeric precursors of differing symmetry (C2v and C4) were prepared, of which only one afforded the desired fused bowl. X-ray crystallographic studies provide conformational insight, and show that the cavitand can bind small molecules in the solid state.

The ground and excited state photophysical properties of a series of fac-[Re(L)(CO)

A series of electronically diverse imines were found to readily react with various donor-acceptor cyclopropyl acid chlorides, with complete regioselectivity, to form 1,3-oxazin-4-ones in moderate yields (25-48% over two steps). Select oxazinones underwent a base induced rearrangement to afford the corresponding cycloheptene-fused oxazinones in good yields (up to 70%).

Hexaphenylbenzene (HPB) and hexa-peri-hexabenzocoronene-(HBC) functionalised 1,2,3-triazoles have been synthesised using an optimised copper(i)-catalysed azide-alkyne cycloaddition (CuAAC) reaction. The coordination chemistry of these ligands was explored through the synthesis of the respective palladium(ii) complexes and their activity as catalysts in the Suzuki-Miyaura reaction assessed.

An enyne metathesis/ring closing metathesis (EM/RCM) sequence was used to synthesise acyloxy-semicyclic dienes from an enyne substrate and various vinyl esters. This allowed convenient access to acyloxy-semicyclic dienes not accessible by cross metathesis alone due to the low reactivity of Fischer carbenes with the termini of 1,3-dienes. This new approach also provides an alternative method for the synthesis of 1-acyloxy-1,3-dienes which are useful reactants for Diels–Alder cycloadditions.

A series of ditopic ω-di(2-pyridylmethyl)amine carboxylic acid ligands incorporating a range of n-alkyl linkers (CnCOOH, n = 3–5, 7, 10 and 11) have been synthesised. Solution phase studies showed a 1 : 1 coordination stoichiometry between the ligands and M(ClO4)2·6H2O (M = ZnII or CuII) in all cases. The ZnII and CuII complexes were subsequently crystallised by liquid–liquid diffusion and the solid-state structures investigated by X-ray crystallography. The crystal structures obtained are entirely consistent with the 1 : 1 metal–ligand ratio of the solution-phase adducts. However, the coordination geometries and complex topologies are dependent on the alkyl chain length of the ligand CnCOOH. The ZnII and CuII complexes of the short alkyl chain ligands (n ≤ 5) exhibit 1D coordination polymeric structures with somewhat different conformations for {[Zn(C3COO)(H2O)](ClO4)·3.5H2O}n (1), {[Zn(C4COO)(H2O)]4(ClO4)4·1.5H2O}n (2), {[Zn(C5COO)(H2O)](ClO4)}n (3), {[Cu(C3COO)](ClO4)·MeOH}n (4), {[Cu(C4COO)(H2O)]2(ClO4)2·2H2O}n (5) and {[Cu(C5COO)(H2O)](ClO4)·2H2O}n (6). In contrast, the ligands with longer alkyl chains (n ≥ 7) participate in Zn2L2 metallomacrocyclic structures {[Zn(C7COO)(H2O)](ClO4)}2 (7), [Zn2(C10COO)2(H2O)2](ClO4)2·2H2O·MeOH (8) and {[Zn2(C11COO)2(H2O)2][Zn2(C11COO)2](ClO4)4·H2O}n (9). The formation of metallomacrocycles instead of the 1D coordination polymers is a persistent trend and, with identical crystal growth conditions and a non-coordinating anion employed, appears to be an effect of the longer alkyl chain.

Tertiary phosphines remain widely utilized in synthesis, most notably as supporting ligands in metal complexes. A series of triarylphosphines bearing one to three hexa-peri-hexabenzocoronene (HBC) substituents has been prepared by an efficient divergent route. These “superphenylphosphines”, P{HBC(t-Bu)5}nPh3-n (n = 1–3), form the palladium complexes PdCl2L2 and Pd2Cl4L2 where the isomer distribution in solution is dependent on the number of HBC substituents. The crystalline structures of five complexes all show intramolecular π-stacking between HBC-phosphines to form a supramolecular bidentate-like ligand that distorts the metal coordination geometry. When n = 2 or 3, the additional HBC substituents engage in intermolecular π-stacking to assemble the complexes into continuous ribbons or sheets. The phosphines adopt HBC’s characteristics including strong optical absorption, green emission, and redox activity.

The ground- and excited-state properties of a series of [ReCl(CO)3(dppz)] complexes with substituted donor groups were investigated. Alteration of donor–acceptor communication through modulation of torsional angle and the number and nature of the donor substituents allowed the effects on the photophysical properties to be characterized though both computational and spectroscopic techniques, including time-dependent density functional theory and resonance Raman and time-resolved infrared spectroscopy. The ground-state optical properties show significant variation as a result of donor group modulation, with an increased angle between the donor and acceptor blue-shifting and depleting the intensity of the lowest-energy transition, which is consistently intraligand charge transfer (ILCT) in nature. However, across all complexes studied there was minimal perturbation to the excited-state properties and dynamics. Three excited states on the picosecond, nanosecond, and microsecond time scales were observed in al...

Four planar tripyridyl ligands (L

A tandem deprotection–cyclization reaction of 1,1-diacylcyclopropanes is described which allows rapid access to structurally diverse 2,3-disubstituted chromones in good yields, and with straightforward purification. The utility of this reaction is showcased by the construction of the potent antibacterial marine natural product bromophycoic acid E scaffold.

1,3-Oxazinen-4-ones are medicinally important scaffolds which have traditionally been accessed using a hetero-Diels-Alder approach or more recently using a cobalt-catalyzed three-component cycloaddition. Herein we report a novel strategy to access this scaffold which allows for the rapid and high yielding synthesis of 1,3-oxazinen-4-ones under ambient temperature and pressures with improved substrate scope.

The ligand 2,3,8,9,14,15-hexa(octyl-thioether)-5,6,11,12,17,18-hexaazatrinaphthalene (HATN-(SOct)6) and its mono-, bi-, and trinuclear Re(CO)3Cl complexes are reported. These are characterized by (1)H NMR spectroscopy and electrochemistry, and show broad, intense absorption across the visible wavelength region. Using time-dependent density functional theory (TD-DFT) calculations and resonance Raman spectroscopy these absorption bands are shown to be π → π*, MLCT, ILCT(sulfur → HATN), or mixed MLCT/ILCT in nature. Time-resolved infrared spectroscopy is used to probe structural changes and dynamics on short time scales and supports the assignment of a mixed MLCT/ILCT state in which both sulfur groups and one metal center act as electron donors to the HATN core.

A series of new cyclopenta-fused triphenylenes has been synthesized in high yield and reacted with [Ru(μ3-Cl)Cp*]4 to form [RuCp*(η6-arene)]PF6 complexes. Systematic variation of the cyclopenta[def]triphenylene allowed the site of complexation to be probed and the influence of the electronic and steric properties of the substituents in directing complexation to be assessed. As determined by NMR spectroscopy and X-ray crystallography, in all cases the [RuCp*]+ fragment complexes at a peripheral arene ring, rather than at the central arene ring or as a neutral η5-cyclopentadienyl metallocene adduct. It was shown that electronic influences are minimal, while steric effects afford selective complexations. The electronic properties of the ligands and complexes were probed with electrochemistry, along with electronic absorption and emission spectroscopies.

Rapid entry into the tricyclic ring system of the illudin family of natural products was achieved using a Diels–Alder cycloaddition of allylidenecyclopropane 7 and various cyclic and acyclic dienophiles. The reaction proceeds with complete regioselectivity and moderate to high stereoselectivity in good to excellent chemical yields.

The donor-acceptor ligands 11-(4-diphenylaminophenyl)dipyrido[3,2-a:2',3'-c]phenazine (dppz-PhNPh2) and 11-(4-dimethylaminophenyl)dipyrido[3,2-a:2',3'-c]phenazine (dppz-PhNMe2), and their rhenium complexes, [Re(CO)3X] (X = Cl(-), py, 4-dimethylaminopyridine (dmap)), are reported. Crystal structures of the two ligands were obtained. The optical properties of the ligands and complexes are dominated by intraligand charge transfer (ILCT) transitions from the amine to the dppz moieties with λabs = 463 nm (ε = 13 100 M(-1) cm(-1)) for dppz-PhNMe2 and with λabs = 457 nm (ε = 16 900 M(-1) cm(-1)) for dppz-PhNPh2. This assignment is supported by CAM-B3LYP TD-DFT calculations. These ligands are strongly emissive in organic solvents and, consistent with the ILCT character, show strong solvatochromic behavior. Lippert-Mataga plots of the data are linear and yield Δμ values of 22 D for dppz-PhNPh2 and 20 D for dppz-PhNMe2. The rhenium(I) complexes are less emissive, and it is possible to measure resonance Raman spectra. These data show relative band intensities that are virtually unchanged from λexc = 351 to 532 nm, consistent with a single dominant transition in the visible region. Resonance Raman excitation profiles are solvent sensitive; these data are modeled using wavepacket theory yielding reorganization energies ranging from 1800 cm(-1) in toluene to 6900 cm(-1) in CH3CN. The excited state electronic absorption and infrared spectroscopy reveal the presence of dark excited states with nanosecond to microsecond lifetimes that are sensitive to the ancillary ligand on the rhenium. These dark states were assigned as phenazine-based (3)ILCT states by time-resolved infrared spectroscopy. Time-resolved infrared spectroscopy shows transient features in which Δν(CO) is approximately -7 cm(-1), consistent with a ligand-centered excited state. Evidence for two such states is seen in mid-infrared transient spectra.

A series of dipyrido[3,2-a:2',3'-c]phenazine (dppz)-based ligands have been synthesised in which phenyl or phenyl-ethynyl linkers are terminated by (t)Bu or CN units. The corresponding [ReCl(CO)3(L)] complexes are also prepared. Electrochemistry shows the ligand which contains a phenyl-ethynyl linker and CN substituent is most easily reduced (by 15 mV relative to the other ligands). All complexes are reduced and oxidised at similar potentials. Electronic absorption spectra are consistent with stabilisation of the LUMO by the binding of the metal centre, as complex spectra are red-shifted relative to their ligand. In addition, those containing phenyl-ethynyl linkers show spectra red-shifted (by 650 cm(-1)) relative to their phenyl-linked analogues. Raman and resonance Raman spectroscopy combined with DFT and TD-DFT calculations are consistent with ligands showing π,π* transitions, and complexes showing metal-to-ligand charge-transfer (MLCT) transitions as the lowest energy absorption. Ligands emit from the π,π* excited state (λem ranging from 450 to 470 nm in CH2Cl2). The complexes show emission from both π,π* and MLCT states; the λem(MLCT) lies at 650-666 nm. Transient lifetimes in CH2Cl2 are decreased by the CN substituent, as this increases knr. Transient resonance Raman spectra (TR(2)) of ligands show spectral features associated with the LC state, and the strong similarities between these and complex spectra support an LC excited state at 355 nm for the complexes. Two-colour TR(3) spectra show only small differences to ground state spectra, the most obvious being a decrease in intensity of C[triple bond, length as m-dash]C bands. For [ReCl(CO)3()] and [ReCl(CO)3()] an increase in intensity of a 1575 cm(-1) band attributed to the dppz˙(-) species suggests that these complexes have significant MLCT state population between 20-60 ns after photoexcitation.

The synthesis of a small family of six electronically and sterically modified 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene gold(I) chloride complexes is described. Additionally, the corresponding trans-[PdBr2(iPr2-bimy)(1,3,4-trisubstituted 1,2,3-triazol-5-ylidene)] complexes are also generated and used to examine the donor strength of the 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene ligands. All compounds have been characterized by 1H and 13C NMR and IR spectroscopy, high-resolution electrospray mass spectrometry (HR-ESI-MS), and elemental analysis. The molecular structures of four of the gold(I) and four of the palladium(II) complexes were determined using X-ray crystallography. Finally, it is demonstrated that these 1,2,3-triazol-5-ylidene gold(I) chloride complexes (Au(trz)Cl) are able to catalyze the cycloisomerization of 1,6-enynes, in high yield and regioselectivity, as well as the intermolecular direct etherification of allylic alcohols. Exploiting the Au(trz)Cl precatalysts allowed the etherification of allylic alcohols to be carried out under milder conditions, with better yield and regioselectivity than selected commercially available gold(I) catalysts.

A series of materials for field effect transistors (FETs), with pyrene at the core and four substituted thiophene arms of different lengths (1-3 thiophene units) have been synthesized using Suzuki cross-coupling reactions and characterized by 1H NMR, 13C NMR, UV-vis absorption, emission spectroscopy, and in one case by X-ray crystallography. © 2010 Elsevier B.V.

A series of electronically diverse imines were found to readily react with various donor–acceptor cyclopropyl acid chlorides, with complete regioselectivity, to form 1,3-oxazin-4-ones in moderate yields (25–48% over two steps). Select oxazinones underwent a base induced rearrangement to afford the corresponding cycloheptene-fused oxazinones in good yields (up to 70%).

In the first phytochemical investigation of Trichuriella monsoniae, three known flavonoidal C-glycosides, isoswertisin 1, 2″-O-β-d-galactosyl isoswertisin 2 and 2″-O-β-d-xylosyl isoswertisin 3 were isolated from the methanolic extract of the whole plant. Their structures were elucidated by extensive NMR spectroscopic studies including 2D NMR and HRMS, and the structure of 2 was supported by single crystal X-ray data studies. Further, NMR assignments for 3 are being reported for the first time.