Marilé Landman

Bio: Marilé Landman is an academic researcher from University of Pretoria. The author has contributed to research in topics: Carbene & Transition metal carbene complex. The author has an hindex of 16, co-authored 67 publications receiving 687 citations. Previous affiliations of Marilé Landman include University of South Africa.

Synthesis and reactivity of metal carbene complexes with heterobiaryl spacer substituents

Abstract: Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M′(CO)5}; M, M′ = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1–20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N′-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved. Alkylation of acyl metallates with triethyloxonium tetrafluoroborate or methyl trifluoromethanesulfonate in THF afforded not only the expected carbene complexes with ethoxy or methoxy substituents, but in the case of bithiophene with methyl trifluoromethanesulfonate, carbene complexes with alkoxy substituents incorporating a ring-opened tetrahydrofuran moiety. X-Ray crystallographic structure determinations were performed on [W(CO)5{C(OMe)(thienylfuran)}] (14), [W(CO)5{C(OMe)(N-methylthienylpyrrole)}] (20) and [{W(CO)5}2{µ-C(OEt)(N,N′-dimethylbipyrrolylC(OEt)}] (12) to assess the role of the heterobiaryl substituent on the structural features of the carbene ligand in the complexes. Complexes [{Cr(CO)5}2{µ-C(OMe)bithienylC(OEt)}] (3), [(CO)5Cr{µ-C(OMe)bithienylC(OMe)}W(CO)5] (5) and [{Cr(CO)5}2{µ-C(OMe)thienylfuranC(OMe)}] (15) were reacted with 3-hexyne to study their behaviour in benzannulation reactions. The major products generated by the biscarbene complexes were regio-selectively determined by the nature of the metal site and that of the heteroatom in the arene rings. The monocarbene complexes [Cr(CO)5{C(OMe)thienylfuran] (13) and [Cr(CO)5{C(OEt)(N-methylthienylpyrrole)}] (19) were refluxed in THF for 2 hours in the presence of [Pd(PPh4)4] to afforded the carbene–carbene coupled olefinic products and small amounts of the corresponding 2-ethyl(biheteroaryl)acetate. By contrast, the biscarbene complex of thienylfuran (15), afforded only the 2,9-diester of thienylfuran.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

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