Showing papers by "Brian W. Skelton published in 2013"
TL;DR: The photochemical mechanisms are illustrated with a combination of NMR, IR, UV-Vis, emission and X-ray structural characterization techniques, clearly demonstrating that the presence of the NHC ligand is responsible for the previously unobserved photochemical behavior in other photoactive tricarbonyl rhenium(I) species.
Abstract: The photophysical and photochemical properties of the new tricarbonyl rhenium(I) complexes bound to N-heterocyclic carbene ligands (NHC), fac-[Re(CO)3(N^C)X] (N^C = 1-phenyl-3-(2-pyridyl)imidazole or 1-quinolinyl-3-(2-pyridyl)imidazole; X = Cl or Br), are reported. The photophysics of these complexes highlight phosphorescent emission from triplet metal-to-ligand (3MLCT) excited states, typical of tricarbonyl rhenium(I) complexes, with the pyridyl-bound species displaying a ten-fold shorter excited state lifetime. On the other hand, these pyridyl-bound species display solvent-dependent photochemical CO dissociation following what appear to be two different mechanisms, with a key step being the formation of cationic tricarbonyl solvato-complexes, being themselves photochemically active. The photochemical mechanisms are illustrated with a combination of NMR, IR, UV-Vis, emission and X-ray structural characterization techniques, clearly demonstrating that the presence of the NHC ligand is responsible for the previously unobserved photochemical behavior in other photoactive tricarbonyl rhenium(I) species. The complexes bound to the quinolinyl-NHC ligand (which possess a lower-energy 3MLCT) are photostable, suggesting that the photoreactive excited state is not any longer thermally accessible. The photochemistry of the pyridyl complexes was investigated in acetonitrile solutions and also in the presence of triethylphosphite, showing a competing and bifurcated photoreactivity promoted by the trans effect of both the NHC and phosphite ligands.
51 citations
TL;DR: The bimetallic ruthenium complex 3(PF6) was quantitatively prepared by treatment of 3 with 1 equiv of [FeCp2]-PF6 at −78 °C and characterized by EPR spectroscopy as mentioned in this paper.
37 citations
TL;DR: In this paper, the reaction between Ru(C≡CH)(dppe)Cp* (1) and oxalyl chloride affords ({Ru(dppecp*)Cp*) 2CO (2) in 72% yield.
37 citations
TL;DR: In this article, a series of Ni(II and Pd(II) complexes of two bidentate and two tetradentate N-heterocyclic carbene (NHC)/amidate ligands have been prepared.
34 citations
TL;DR: In this paper, the first three complexes were investigated for their photophysical properties, highlighting phosphorescent emission from their triplet metal-to-ligand charge transfer excited states, although in the case of the dinuclear species the quantum yield was found to be extremely low.
28 citations
TL;DR: Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin-resistant Staphylococcus aureus MRSA, highlighting the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development.
Abstract: Herein we describe the preparation and structure-activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin-resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 10442). Compound 10 was most active against Moraxella catarrhalis with minimum inhibitory concentrations (MICs) of 0.12-0.25 μg mL-1 and against Staphylococcus spp. with MICs ranging from 2-4 μg mL-1. The derivative 17 showed increased activity with MICs of 0.06-0.25 μg mL-1 against M. catarrhalis and 0.12-1 against Staphylococcus spp. This level of activity is similar to that reported for S. aureus for antibiotics, such as vancomycin, with MICs of ≤2.0 μg mL-1 and clindamycin with MICs of ≤0.5 μg mL -1. As an indicator of toxicity, 17 was tested for its ability to lyse sheep erythrocytes, and showed low haemolytic activity. Such results highlight the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development. Routes to new antibiotics: The preparation of and structure-activity relationship studies on a range of stilbene based compounds revealed two related compounds, each bearing carboxylic acid moieties, exhibiting pronounced activity against several bacterial strains including methicillin-resistant Staphylococcus aureus, MRSA (see scheme, dba = dibenzylidene acetone).
25 citations
TL;DR: Adducts of a number of tertiary pnicogen ligands ER(3) and -arsine, AgSCN are structurally and spectroscopically characterized and the wavenumbers of the ν(CN) bands in the IR spectra are in broad agreement with the empirical rule that distinguishes bridging from terminal bonding.
Abstract: Adducts of a number of tertiary pnicogen ligands ER3 (triphenyl-phosphine and -arsine (PPh3,AsPh3), diphenyl,2-pyridylphosphine (PPh2py), tris(4-fluorophenyl)phosphine (P(C6H4-4F)3), tris(2-tolyl)phosphine (P(o-tol)3), tris(cyclohexyl)phosphine (PCy3)), with silver(I) thiocyanate, AgSCN are structurally and spectroscopically characterized. The 1:3 AgSCN:ER3 complexes structurally defined (for PPh3,AsPh3 (diversely solvated)) take the form [(R3E)3AgX], the thiocyanate X = NCS being N-bound, thus [(Ph3E)Ag(NCS)]. A 1:2 complex with PPh2py, takes the binuclear form [(pyPh2P)2Ag(SCNNCS)Ag(PPh2py)2] with an eight-membered cyclic core. 1:1 complexes are defined with PPh2py, P(o-tol)3 and PCy3; binuclear forms [(R3P)Ag(SCNNCS)Ag(PR3)] are obtained with P(o-tol)3 (two polymorphs), while novel isomeric tetranuclear forms, which may be envisaged as dimers of dimers, are obtained with PPh2py, and, as further polymorphs, with PCy3; these latter may be considered as extensions of the ‘cubane’ and ‘step’ forms previously described for [(R3E)AgX]4 (X = halide) complexes. Solvent-assisted mechanochemical or solvent-assisted solid-state synthesis methods were employed in some cases, where complexes could not be obtained by conventional solution methods, or where such methods yielded a mixture of polymorphs unsuitable for solid-state spectroscopy. The wavenumbers of the ν(CN) bands in the IR spectra are in broad agreement with the empirical rule that distinguishes bridging from terminal bonding, but exceptions occur for compounds that have a double SCN bridged dimeric structure, and replacement of PPh3 with PPh2py apparently causes a significant decrease in ν(CN) to well below the range expected for bridging SCN in these structures. 31P CP MAS NMR spectra yield additional parameters that allow a correlation between the structures and spectra.
23 citations
TL;DR: In this paper, N-Heterocyclic carbene ligands derived from C 2-symmetric diamine with naphthyl side chains are introduced as chiral monodentate ligands, and their palladium complexes (NHC)Pd(cin)Cl are prepared.
Abstract: N-Heterocyclic carbene ligands derived from C
2-symmetric diamine with naphthyl side chains are introduced as chiral monodentate ligands, and their palladium complexes (NHC)Pd(cin)Cl are prepared. These compounds exist as a mixture of diastereomers, and the palladium complexes can be successfully separated. When used in the asymmetric Suzuki–Miyaura and Kumada coupling, chiral biaryls can be obtained in high yield and moderate selectivity.
23 citations
TL;DR: The reaction of 2-pyridyltetrazolate with [Re(CO)5X] (X = Cl, Br) yielded the formation of an unexpected cyclic metallacalix[3]arene, as revealed by X-ray structural studies, characterised by aqua emission and reversible three-electron oxidation.
Abstract: The reaction of 2-pyridyltetrazolate with [Re(CO)5X] (X = Cl, Br) yielded the formation of an unexpected cyclic metallacalix[3]arene, as revealed by X-ray structural studies, characterised by aqua emission and reversible three-electron oxidation.
21 citations
TL;DR: An efficient synthetic sequence involving carbonylation, formation of a β-keto-sulfoxide, and cyclization is presented en route to the antibiotic and antitumor compound (±)-BE-26554A.
21 citations
TL;DR: The interplay of the components have been investigated using Hirshfeld surface analysis, with the nature of the species in aqueous solution in the absence of the paramagnetic lanthanide ions studied using 1 H NMR and modeled using molecular simulations as mentioned in this paper.
Abstract: p-Sulfonatocalix(5)arene forms host−guest complexes in the solid state with hydroxyl-functionalized imidazolium and bis-imidazolium cations, also involving gadolinium(III) ions which form a coordination polymer through the sulfonate groups of the calixarene. The interplay of the components have been investigated using Hirshfeld surface analysis, with the nature of the species in aqueous solution in the absence of the paramagnetic lanthanide ions studied using 1 H NMR and modeled using molecular simulations.
TL;DR: In this paper, the preparation, characterization, and single-crystal X-ray diffraction molecular structure determinations of four complexes containing metal-ligand centers linked by chains of C(sp) atoms are described.
Abstract: As part of an extensive investigation into the chemistry of complexes containing metal-ligand centers linked by chains of C(sp) atoms, the preparation, characterization, and single-crystal X-ray diffraction molecular structure determinations of four complexes {MLn}-C≡CC≡C-{M′L′m} [MLn = Ru(dppe)Cp*, M′L′m = Fe(dppp)Cp* (1), Ru(dppe)Cp* (2), MLn = M′L′m = Os(PPh3)2Cp (3)], and {Cp*(dppe)Ru}C≡CC≡C{trans-RuCl(dppe)2} (4), in which the alternating C(sp)–C(sp) bonds have values between 1.375 and 1.40 A (single) and between 1.20 and 1.259 A (triple), respectively, are described. In addition, a structure determination of Ru3(μ-H){μ3-C2C≡C[Ru(PPh3)2Cp]}(CO)9 (5) shows that the C2 fragment attached to the HRu3 cluster shows the expected lengthening [to 1.311(7) A] and bending at the two carbon atoms [to 152.6(6) and 157.6(5)°] (resulting from back-bonding from the Ru3 cluster into the C≡C π* orbitals) compared with the essentially linear Ru–CC– moiety [C≡C 1.222(6) A, angles at C of 178.0(5), 172.3(6)°],
TL;DR: Three bisannulation strategies have been used to rapidly construct pentacyclic benzo-fused pyrrolo[4,3,2-mn]acridines, similar to several biologically active natural products as mentioned in this paper.
TL;DR: In this article, 1,10-phenanthroline reacts with malonitrile and aldehydes in the presence of isocyanides as domino-Knoevenagel-nucleophilic cycloaddition for generation of a new class of 10-(aryl)-11-(alkyl- or arylamino-)pyrrolo[1,2-a][1,10]phenanthusline-9-carbonitrile compounds in excellent yield.
TL;DR: In this paper, a 1 to 2 mol-ratio reaction of LnCl3 with Na2(PDDA) in aqueous solution yielded 2H2O, structurally characterized for Ln = Ce (1), Sm (2) (redetermination), Tb (3) and Y (4) in monoclinic C2/c array.
Abstract: Reaction of LnCl3 with Na2(PDDA) (PDDA = phenylene-1, 2-dioxydiacetate) in a 1 to 2 mol ratio in aqueous solution yielded [Ln2(PDDA)3(H2O)6]•2H2O, structurally characterized for Ln = Ce (1), Sm (2) (redetermination), Tb (3) and Y (4) in a monoclinic C2/c array, a second related structural form [orthorhombic, Pbcn] being obtained for Tb (5), Ho (6) and Er (7). The 'domains of existence' of these two previously described forms are now extended to Ce–Dy, Y, and Eu–Er, respectively. Reaction under the same conditions for the heavier Yb3+ ion yielded [Yb2(PDDA)3(H2O)6](∞|∞)•4H2O (8), orthorhombic, Pbca. In the case of Ln = La the bimetallic species [NaLa(PDDA)2(H2O)2](∞|∞)•4H2O (9) was obtained, while reaction of LnCl3 with Na2(PDDA) in a 1 to 3 mol ratio led to the isolation of the isotypic (monoclinic, P21/c) [NaLn(PDDA)2(H2O)2](∞|∞)•4H2O) for Ln = Ce (10) and Sm (12). With the smaller Ln = Yb, the more definitively bimetallic [NaYb(PDDA)2(H2O)2](∞|∞)•3H2O (13) (triclinic, Pequation image)) was obtained, the trihydrate solvation ascribed differing from that recorded (dihydrate) in a cosynchronous report.
TL;DR: The title compound, [Co(C8H9N4O)2]Cl·0.5H2O, is a solvatomorph of the corresponding trihydrate, where the ligand molecules are deprotonated at the phenol O atom and octahedrally coordinate the CoIII atoms through the azomethine N and phenolate O atoms in a mer configuration.
Abstract: The title compound, [Co(C8H9N4O)2]Cl·0.5H2O, is a solvatomorph of the corresponding trihydrate. Unlike in the structure of the latter compound, there are two different cations in the asymmetric unit of the title compound. The ligand molecules are deprotonated at the phenol O atom and octahedrally coordinate the CoIII atoms through the azomethine N and phenolate O atoms in a mer configuration. In the crystal, the cations, chloride ions and lattice water molecules are linked by N—H⋯O, N—H⋯Cl, O—H⋯Cl and O—H⋯O interactions, forming a two-dimensional network parallel to (10-1).
TL;DR: In this paper, the Hirshfeld surface approach and a tri-cationic structural synthon extracted from the asymmetric units has been analyzed and quantified using the common underlying pattern of close intercomponent approaches.
Abstract: Salts of the family [M(NCMe)4]+X− (M = Cu, Ag; X− = [BF4]−, [ClO4]−, [PF6]− crystallize in the space groups Pna21 or P212121 with very similar cell dimensions. This gives rise to two sets of true isomorphs (four members in Pna21, two in P212121), and a solvated species (Cu/PF6/MeCN) with a distorted P212121 lattice. Across the two space groups and regardless of the choice of metal atom or anion, the underlying basic structures are virtually identical in the six unsolvated cases, consisting of alternate sheets of cations and anions, mainly held together by C–H⋯C,N and C,N⋯C,N interactions, and a columnar cation–anion motif perpendicular to the sheets maintained by C–H⋯F,O interactions. The pair of concomitant polymorphs found with Cu/BF4 in both Pna21 and P212121 can readily be described as being quasi-isomorphous. Using a Hirshfeld surface approach and a tri-cationic structural synthon extracted from the asymmetric units, the common underlying pattern of close intercomponent approaches has been analysed and quantified. The structure of the Ag/PF6 complex is new; low-temperature redeterminations are recorded for the Ag/ClO4 and the Cu/PF6/MeCN complexes.
TL;DR: The title compound, [Cu2(C9H10NO2)4], is built of discrete centrosymmetric dimers that pack relative to each other in such a way that the Cu2O2 planes of adjacent dimers are orthogonal.
Abstract: The title compound, [Cu2(C9H10NO2)4], is built of discrete centrosymmetric dimers. The CuII atoms are each five coordinated by two deprotonated Schiff base ligands that are bonded differently to the metal atoms. Of the two phenolate O atoms, one is coordinated to one CuII atom, whereas another bridges the two metal atoms. The basal plane of the square pyramid around CuII atoms is formed by the imino N and phenolate O atoms of the bidentate and the monodentate/bidentate Schiff base ligands. The bridging phenolate oxygen occupies the apical position of the coordination sphere with a considerably longer Cu—O bond length. In the crystal, the dimeric molecules pack relative to each other in such a way that the Cu2O2 planes of adjacent dimers are orthogonal.
TL;DR: In this article, Ni(PymNH2)2(5-BrSal-H)2]n·2dmf has been synthesized and characterized by elemental analysis, X-ray crystallography and infrared spectroscopy.
TL;DR: In this article, a novel complex PNC was tested in the title reactions to produce the chiral biaryls with low to moderate e.e.s, and the results showed that the PNC can be used to produce chiral Biaryls of low and moderate degree.
Abstract: A novel complex PNC is tested in the title reactions to produce the chiral biaryls with low to moderate e.e′s.
TL;DR: The conformationally restricted glutamate analogues, 3-alkyl-1-amino-2-cyclopentene-1,3-dicarboxylates and N-alksylated analogues have been prepared in a regioselectives and diastereoselective manner and compound 13b was found to be the most potent antagonist at mGluR2.
TL;DR: In this article, a two-dimensional polymer was constructed for 1,2-bis(diphenylarsino)ethane using a single crystal X-ray structure determination, where the potassium atoms were linked by bridging 1,4-dioxane units, the oxygen atoms of which formed a quasi-square planar array about the potassium atom.
Abstract: In attempting the metallation of 1,2-bis(diphenylarsino)ethane, the title compound KAsPh2·2(1,4-dioxane) was obtained and characterised with a single crystal X-ray structure determination. Like the sodium counterpart, which is a monosolvate, NaAsPh2·1,4-dioxane, the complex may be considered as a two-dimensional polymer, the potassium atoms being linked by bridging 1,4-dioxane units, the oxygen atoms of which form a quasi-square planar array about the potassium atom (K–O 2.676–2.839(3) A). Unlike the sodium complex, in which arsenide bridging is an intrinsic motif in the construction of the polymer, the K⋯As distance here is long (3.4662(10) A), with the anion being terminal/monodentate, and counterposed in what may be considered a quasi-octahedral coordination sphere, by a trans-approach to two atoms of a neighbouring aromatic ring (K⋯C(ar) 3.361, 3.416(4) A), extending the polymer in the third dimension.