51 research outputs found

    2-(Biphenyl-4-yl)propan-2-ol

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    The title compound, C15H16O, crystallizes with two independent mol­ecules in the asymmetric unit. Due to the space-group symmetry, this results in the formation of a tetra­mer where the four mol­ecules are connected by O—H⋯O hydrogen bonds. The mol­ecules pack parallel to the c axis. Both mol­ecules in the asymmetric unit are nonplanar and the dihedral angles between connected aromatic rings in each mol­ecule are 7.96 (12) and 9.75 (13)°. This contrasts with the gas phase density functional theory (DFT) optimized conformation, where this dihedral angle is 39.33°

    Orientation of trimethylolethane cyclic phosphite in rhodium complexes : structure of [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)]

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    Density functional theory calculations showed that rotation of the (P(OCH2)3CCH3) group in the rhodium-acetylacetonato complex [Rh(acac)(CO)(P(OCH2)3CCH3)] has a negligible influence on the energy of the complex. Density functional theory calculations further showed that the minimum energy orientation of the cyclic (P(OCH2)3CCH3) group in square planar rhodium- (P(OCH2)3CCH3)-(CO) complexes containing a bidentate ligand that is larger than the acetylacetonato ligand, is with one of the P-O bonds near parallel (within 10°) to the plane defined by the four atoms coordinated to Rh. The three P-O bonds of the rigid (P(OCH2)3CCH3) group adopt a C3-symmetrical conformation around the Rh-P axis. The lowest energy geometry of [Rh(BID)(CO)(P(OCH2)3CCH3)] (BID = bidentate ligand with two O donor atoms and charge -1) complexes is where one P-O bond is aligned near parallel to the Rh-OBID trans to CO bond, while the geometry with a P-O bond orientated near parallel to the Rh-CCO bond, is slightly higher in energy, but still possible experimentally. The highest energy orientation of the (P(OCH2)3CCH3) group in square planar [Rh(BID)(CO)(P(OCH2)3CCH3)] complexes, is with one of the P-O bonds near perpendicular to the plane described by the four atoms coordinated to Rh. The orientation of the cyclic (P(OCH2)3CCH3) group in available experimental structures of square planar [Rh(BID)(CO) (P(OCH2)3CCH3)] complexes, confirms this finding.The South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.http://www.elsevier.com/locate/poly2017-06-30hb2016Chemistr

    Geometrical isomers of tris(beta-diketonato)metal(III) complexes for M = Cr or Co: Synthesis, X-ray structures and DFT study

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    Solid state crystal data of three tris(b-diketonato)metal(III) complexes (M = Cr or Co), representative of the three different molecular symmetries that these complexes can obtain, namely D3, C3 or C1 symmetry, are presented and compared with related experimental structures. Density functional theory calculations show that both fac and mer isomers of tris(b-diketonato)metal(III) complexes containing unsymmetrical b-diketonato ligands can exist, in agreement with experimental NMR data. The orbital ordering for both the S = 3/2 [Cr(acac)3] and S = 0 [Co(acac)3] (Hacac = acetylacetone) complexes in order of increasing orbital energy is: dxy < dxz; dyz < dz2 ; dx2 y2 .South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.http://www.elsevier.com/locate/ica2017-06-30hb2016Chemistr

    Conformational preferences of heteronuclear Fischer carbene complexes of cymantrene and cyclopentadienyl rhenium tricarbonyl

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    Homo- and heteronuclear bimetallic carbene complexes of group VII transition metals (Mn and Re), with cymantrene or cyclopentadienyl rhenium tricarbonyl as the starting synthon, have been synthesized according to classic Fischer methodology. Crystal structures of the carbene complexes with general formula [RC5 H4  M'(CO)2 {C(OEt)(C5 H4  M(CO)3 )}], where M = M′ = Mn, R = H (1), R = Me (2); M = Mn, M′ = Re, R = H (3); M = M′ = Re, R = H (4); and M = Re, M′ = Mn, R = H (5), are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the binuclear complexes. Application of second-order perturbation theory (SOPT) of the NBO method revealed stabilizing interactions between the methylene C–H bonds and the carbonyl ligands of the carbene metal moiety. Energy calculations in the gas phase of the cis and trans conformations of the Cp rings relative to one another are comparable, with the trans conformation slightly lower in energy. The theoretical findings have also been confirmed with single-crystal X-ray diffraction, and all solid-state structures are found in the trans geometry.The South African National Research Foundation [grant number 93638] and the University of Pretoria.http://www.tandfonline.com/loi/gcoo202017-09-30hb2016Chemistr

    Jahn-Teller distortion in tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]manganese(III) isomers : an x-ray and computational study

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    The solid state crystal data of a mer isomer of the [Mn(CF3COCHCOC4H3S)3] complex, [Mn(tfth)3], exhibits elongation Jahn-Teller distortion (elongation of the metal-ligand bonds along the z-axis and shortening of the metal-ligand bonds along both the x and y-axes). Density functional theory calculations (DFT) show that one fac and three mer isomers of [Mn(tfth)3] can exist. The difference between the three mer isomers of [Mn(tfth)3] is that the Jahn-Teller elongation of the two trans axial Mn-O bonds along the zaxis occur along three different Otfth-Mn-Otfth bonds. DFT calculations further show that the ground state geometry of all the [Mn(tfth)3] isomers exhibits elongation Jahn-Teller distortion.South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.http://www.elsevier.com/locate/molstruc2017-09-30hb2016Chemistr

    X-ray and electronic structure of tris(benzoylacetonato-κ2O,O')iron(III)

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    Solid state crystal data of d5 tris(benzoylacetonato-k2O,O0)iron(III), [Fe(ba)3], are presented. The mer isomer crystallized in the solid state. Density functional theory calculations show that both fac and mer isomers of [Fe(ba)3] can exist. Both fac and mer [Fe(ba)3] are high spin d5 complexes with the same ordering of the d-based molecular orbitals in order of increasing orbital energy, namely dxy < dyz z dxz < dz2 z dx2-y2.South African National Research Foundation (Grant No: 93442) and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.http://www.elsevier.com/ locate/molstruc2017-11-30hb2016Chemistr

    Crystal and electronic structures of tris[4,4,4-Trifluoro-1-(2-X)-1,3-butanedionato]iron(III) isomers (X = thienyl or furyl) : an X-ray and computational study

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    Please read abstract in the article.Norwegian Supercomputing Program (NOTUR) (Grant No. NN4654K), the South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein.http://www.elsevier.com/locate/molstruchb2014ai201

    Electrochemistry of Fischer alkoxycarbene complexes of chromium : the use of Density Functional Theory to predict and understand oxidation and reduction potentials

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    The electrochemical behaviour of a series of Fischer ethoxycarbene complexes of the type [(CO)5Crdouble bond; length as m-dashC(OEt)R] with R = 2-thienyl (1), 2-furyl (2), 2-(N-methylpyrrolyl) (3), N-methyl-2-(2′-thienyl)pyrrole) (4) and 2,2′-thienylfuran (5), is investigated by means of cyclic voltammetry. Results show that the first one electron reduction process is sensitive to the energy, shape and distribution of the LUMO orbital, leading to a linear relationship between the formal reduction potential and the LUMO energy: E0′(Ccarbene) = –0.70 ELUMO–3.44 (R2 = 1.00) which is valid over a large potential range. The dimeric heteroarene substituents of 4 and 5 lead to enhanced stabilization of the reduced complexes 4 and 5, making another one electron reduction possible. The formal reduction potential, E0′(Cr) of the first oxidation process of 1–5 lays within a narrow potential range of 0.43–0.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carbon.http:// www.elsevier.com/locate/electactahb2014ai201

    Conformation of a MnCP(CO)2-thienothiophene carbene complex : a spectroscopic and computational study

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    The carbine complex [MnCp(CO)2C(OEt)(TT)], (TT = 3,6-dimethylthieno[3,2-b]thiophene) 1, was synthesized according to the classical Fisher method. The novel complex was fully characterized using various spectroscopic techniques. The infrared spectrum of the complex, recorded as a solution in dichloromethane, revealed a four-band spectrum in the carbonyl region instead of the expected two-band spectrum. A density functional theory (DFT) study was undertaken to explain the presence of more than one conformer in solution. The crystal structure of 1 is reported.http://www.elsevier.com/locate/molstru

    Facile Suzuki-Miyaura coupling of activated aryl halides using new CpNiBr(NHC) complexes

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    Nine new Ni(II)-NHC complexes, [CpNiBr(NHC)], were synthesised from nickelocene and the corresponding symmetric or asymmetric alkyl/-benzyl/phenylethyl imidazolium bromide ligands in relatively high yield. Access to each of the synthesised symmetric or asymmetric alkyl/benzyl/phenylethyl imidazolium bromide salts was obtained through deprotonation of imidazole, followed by treatment with an alkyl- or aryl halide, which is subsequently followed with reaction of a secondary alkyl-, benzyl-, or phenylethyl halide. The series of [CpNiBr(NHC)] exhibited catalytic activity in the Suzuki-Miyaura coupling of activated aryl halides with phenylboronic acid to give the respective biphenyl and biphenyl-containing products. In general, the more electron-donating NHC-bearing Ni complexes showed higher activity with aryl halides bearing electron-withdrawing functionalities including carboxaldehyde moieties. All complexes were characterised by 1H- and 13C-NMR spectroscopy, FT-IR spectroscopy, CHN and MS analyses, along with six selected single crystal X-ray structures that are reported here.The National Research Foundation of South Africa (NRF) and the University of Pretoria (UP).http://www.elsevier.com/locate/jorganchem2017-07-31hb2016Chemistr
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