29 research outputs found

    Chalcogen controlled redox behaviour in peri-substituted S, Se and Te naphthalene derivatives

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    Cyclic and square wave voltammetry of (PhE)2 peri-disubstituted naphthalene[1,8-cd]dichalcoganyls and acenaphthene[5,6-diyl]dichalcoganyls (E = S, Se, Te, 12 compounds) is reported. Mixed (E1 = Se, Te; E2 = Br, I) naphthalene[1,8-cd]halochalcoganyls were also investigated, as well as an exemplar bearing two PhS([double bond, length as m-dash]O) groups and another bearing one PhSe and one Ph2P([double bond, length as m-dash]S) substituent. The voltammetry, in CH2Cl2/0.4 M [nBu4N][PF6] at both platinum and glassy carbon macro-disk working electrodes, shows two sequential chemically reversible and electrochemically quasi-reversible oxidation processes, and the lack of accessible reductions. Additional oxidations above +1.5 V vs. Fc+/0 have not been investigated in detail. In situ and ex situ EPR spectroscopy conclusively demonstrate that both anodic processes are 1e transfers; persistent radical cations could be generated for all the dichalcoganyls except when E1 = E2 = Te; for the latter case thermally stable dications are generated instead. The complex possible solution conformations of these compounds in 0, +1 and +2 charge states were modelled with DFT at the B3LYP-D3(BJ)/6-31+G(d) level of theory in a CH2Cl2 PCM continuum solution model and adiabatic ionisation energies calculated, which correlate linearly (R = 0.88) with the Ea1p values. Crystal structures of four solvolysis and hydrolysis products of the ditellurium dications are reported and were modelled computationally. Interpretative comparisons to unsubstituted naphthalene[1,8-cd]dichalcogenoles are reported and the crystal structure of naphtho(1,8-cd)(1,2-dithiolium) tetrafluoroborate has been obtained. This is the first structure reported for any salt of this cation radical. Electron transfer mechanisms of both the (PhE)2 and E2 peri-disubstituted naphthalene series are correlated using a redox molecular orbital interpretative framework

    Synthesis, electronic structures and electrochemistry of 3-triarylphosphoraniminato-1,3,5-trithia-2,4,6,8-tetrazocines: detection of trithiatetrazocinyl radical anions

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    Sherpa Romeo green journal. This is the peer reviewed version. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Reaction of the bicyclic sulfur-nitrogen heterocycles RC6H4CN5S3 (R = 4-CH3O, 4-CH3, 4-H, 4-Cl, 4-CF3, 3-CF3, with PR’3 (R’ =C6H5 or 4-CH3OC6H4) produces 3-phosphoraniminato-7-aryl-1,3,5-trithia-2,4,6,8-tetrazocines RC6H4CN4S3NPR’3. In all cases, only the endo-isomers were isolated and characterized by 1H, 31P, and 19F NMR, UV spectroscopy, and X-ray crystallography. RB3LYP/6-311+G(d,p)// RB3LYP/6-31G(d,p) computations were undertaken to help explain the atom-exact syntheses via intermediates previously detected spectroscopically. Three reasonable intermediates have been computed as stationary points with energies consistent with the observed reaction path. Cyclic and square wave voltammetry studies of RC6H4CN4S3NPR’3 using a glassy carbon working electrode in CH2Cl2 with 0.4 M [nBu4N][PF6] all displayed two IRR reduction processes at RT at approximately –1.9 V and –2.2 V, respectively, and one IRR oxidation process at approximately 1.0 V (versus Fc+/0). [RC6H4CN4S3NPR’3]–• radical anions (R’ = 4-CH3OC6H4, R = 4- CH3O, 4-H, 4-CF3,) were detected at -50 °C in CH2Cl2 by in-situ electrolysis and simultaneous electron paramagnetic resonance spectroscopy: [4-RC6H4CN4S3NP(4-CH3OC6H4)3]–•, estimated a(31P) = 0.078 mT, a(14N1) = 0.031 mT, a(14N2,3) = 0.256 mT, a(14N4,5) = 0.341 mT. The signals decay rapidly but after electrolysis is ended, a persistent EPR signal is always obtained with EPR parameters that match for known 4-aryl-1,2,3,5-dithiadiazolyls, e.g. a(N) = 0.51 mT and g = 2.0105, consistent with production of [4-CF3-C6H4CN2S2]•.Ye

    Mono‐ and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis‐1,4‐([3]Cumulene)‐p-carboquinoid System

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    An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.peerReviewe

    Mono- and bis-imidazolidinium ethynyl cations and the reduction of the latter to give an extended bis-1,4-([3]cumulene)-p-carbo-quinoid system

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    Sherpa Romeo yellow journal. This is the peer reviewed version. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsAn extended π-system containing two [3]cumulene fragments separated by a p-carbo-quinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis-imidazolidinium ethynyl cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carbo-quinoid due to the πaccepting properties of the capping NHCsYe

    Crystal structure of bis(triphenylphosphonium) hexabromadigallate(II) in the correct space group: conformational complexity in a heteroethan

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    Sherpa Romeo green journal. Open access article. Creative Commons Attribution 4.0 License (CC-BY) appliesThe crystal structure of [Ph3PH]2[Ga2Br6], previously described as having a disordered anion in the space group R̄ 3, has been re-determined in the correct space group P̄ 3, where it is fully ordered. Interestingly, two-thirds of the [Ga2Br6]2− dianions have an intermediate conformation with a Br–Ga–Ga–Br torsion angle of 36.91 (1)°, while the remaining is staggered as required from adopting a site with inversion symmetry. In the lattice, [Ph3PH]+ ions lie along the same threefold axes as the dianions and are oriented such that the P–H bond is directed towards a gallium atom. The phosphonium ions lie back-to-back and interact with relatively strong T-interactions between phenyl rings on adjacent cations. DFT calculations at the B3LYP/6–311+G(fd,) level have been used to determine the barriers to rotation in [Ga2X6]2− ions. For X = Cl and X = Br, the barriers are found to be very small, with values of 4.3 and 5.1 kJ mol−1 for the two halogens.Ye

    Group 13 complexes of dipyridylmethane, a forgotten ligand in coordination chemistry

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    The reactions of dipyridylmethane (dpma) with group 13 trichlorides were investigated in 1 : 1 and 1 : 2 molar ratios using NMR spectroscopy and X-ray crystallography. With 1 : 1 stoichiometry and Et2O as solvent, reactions employing AlCl3 or GaCl3 gave mixtures of products with the salt [(dpma)2MCl2]+[MCl4]− (M = Al, Ga) as the main species. The corresponding reactions in 1 : 2 molar ratio gave similar mixtures but with [(dpma)MCl2]+[MCl4]− as the primary product. Pure salts [(dpma)AlCl2]+[Cl]− and [(dpma)AlCl2]+[AlCl4]− could be obtained by performing the reactions in CH3CN. In the case of InCl3, a neutral monoadduct (dpma)InCl3 formed regardless of the stoichiometry employed. A neutral adduct (dpma)(BCl3)2 was obtained from the reaction between dpma and BCl3 in Et2O using 1 : 2 stoichiometry. With 1 : 1 molar ratio of reagents, a mixture of products and deprotonation of the methylene bridge in [(dpma)BCl2]+ was observed. The experimental data showed that the structural flexibility of the dpma ligand results in more diverse coordination chemistry with group 13 elements than that observed for bipyridine (bpy), while computational investigations indicated that the investigated metal–ligand interactions are, to a first approximation, independent of the ligand type. Electrochemical and chemical attempts to reduce the cations [(dpma)MCl2]+ showed that, in stark contrast to the chemistry of the related [(bpy)BCl2]+ cation, the neutral radicals [(dpma)MCl2]˙ are extremely unstable. Differences in the redox behaviour of dpma and bpy could be rationalized with the electronic structure of the ligand and that of the methylene bridge in particular. As a whole, the facile reactivity of the methylene bridge in the dpma ligand renders it amenable to further reactivity and functionalization that is not possible in the case of bpy.peerReviewe

    Coordination complexes of thiazyl rings: Synthesis, structure and DFT computational analysis of CpCr(CO)x (x = 2,3) complexes of fluorinated and non-fluorinated 1lamda^3-1,2,4,6-thiatriazinyls, with differing Cr—S bond orders.

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    Sherpa Romeo green journal. Permission to archive accepted author manuscript.Reaction of [3,5-Ph2-C2N3S]2 with [CpCr(CO)3]2 in toluene at RT forms an adduct via a Cr—S bond, formulated as CpCr(CO)3SN3C2Ph2, which has fitting NMR, IR and combustion analysis data. The structure was determined by a single-crystal X-ray structure diffraction study (P21/n, a = 8.4611(17)Å; b = 20.509(4) Å, c = 11.757(2) Å, = 104.453(7)°). The Cr—S bond-length = 2.4908(11) Å corresponds to a bond-order of 1.0 from > 90 values for CpCr(CO)x or Cp*Cr(CO)x moieties (x = 2,3) bonded to S which are used to establish a Pauling-type bond order scale specific to this class of compounds. Similar reactions of fluorinated thiatriazinyls derived from [3-Ph-5-CF3-C2N3S]2 or [4-MeOC6H4-5-CF3-C2N3S]2 are accompanied by the loss of CO to produce CpCr(CO)2SN3C2PhCF3 (P, a = 8.0929(8) Å; b = 10.3160(10) Å, c = 11.2405(11), = 70.032(2)°, = 72.076(2)°, = 82.375(2)° ) and CpCr(CO)2SN3(CCF3)(C6H4OCH3) (P21/c, a = 8.1311(7)Å; b = 24.284(2) Å, c = 9.1025(8) Å, = 97.218(2)°), also fully characterized by spectroscopy and crystallography. Their measured Cr—S bond-lengths, 2.2987(14) Å and 2.2965(11) Å, correspond to bond orders of 1.5. (U/R)B3PW91/6-311+G(2df,2p)//B3PW91/6-31G(2d,p) hybrid DFT calculations show that the tricarbonyl complex has an unusual bond. However, the dicarbonyl complexes of the fluorinated thiatriazinyls are -bonded.Ye

    A variable temperature X-ray diffraction investigation of [PPN+][S4N5]: supramolecular interactions governing an order/disorder transformation and the first high resolution X-ray structure of the anion

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    Sherpa Romeo green journal. Open access article. Creative Commons Attribution 3.0 LIcense (CC BY 3.0) appliesThe title salt, triphenyl(P,P,P-triphenylphosphineimidato-N)-phosphorus(1+) 1,3,5,7-tetrathia(1,5-SIV)-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1,4,6,7-tetraene(1−), CAS [48236-06-2], prepared by the literature method, is found by crystallography to be a 1:1 CH3CN solvate. Disorder exists for the N atoms of the anion. A VT crystal structure study was conducted at 100 K, 120 K, 140 K, 172 K, 200 K, 240 K and 280 K. The 100 K structure is superior, with only 10% of a second anion position oppositely-oriented w.r.t the diad axis of point group 2mm. At 120 K, an adjacent two-site disorder is encountered, but at higher temperatures three-site disorder with both opposite and adjacent placements of S4N5 − ions is required w.r.t. the primary component. At 240 and especially 280 K, the anion nitrogen atoms appear fully scrambled amongst the six possible sites on the edges of an S4 tetrahedron with 83.3% occupancy for each. The PPN+ geometry does not show strong cation-cation interactions. However, there are numerous supramolecular contacts corresponding mostly to non-classical H-bonds between PPN+ ions and S4N5 − as well as CH3CN. The geometry of the anion is corroborated from B3LYP/6-311++G(3df) DFT calculations, and the infra-red spectrum was assigned with excellent agreement between experimental and calculated frequencies.Ye
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