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  • General Chemistry  (4)
  • KeywordsAb initio calculations, Phosphorus heterocycles, Small ring systems, 31P NMR  (1)
  • 1
    Electronic Resource
    Electronic Resource
    HP4 - and (CH2)P3 - Anions Form Four-membered Rings with an Allyl Moiety – An ab initio/NMR study (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 289-298 
    Details
    ISSN: 0948-5023
    Keywords: KeywordsAb initio calculations, Phosphorus heterocycles, Small ring systems, 31P NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract On the energy hypersurfaces of the anions HP4 - and CH2P3 - at the RMP2(fc) /6-31+G(d) level, the isomers with triphosphaallyl moiety are the lowest energy structures. For these free 1-X-2,4-(PB)2-3-PA - anions characteristic 31P NMR chemical shifts, are predicted to be (for X = PH, 1, δ31P(PA) = 517, δ31P(PB) = 424, and δ31P(PX) = 50; for X = CH2, 4, δ31P(PA) = 611, δ31P(PB) = 450). The observed δexp 31P values for HP4 - (Na/K, DME) completely disagree with the δ31P calculated at GIAO/MP2/6-311+G(d) //RMP2(fc) /6-31+G(d) for structure 1. The rotational average of the phosphinidyltriphosphirene structures (P3-PH-, 3) agree better with the δexp 31P than those with a bicyclo[1.1.0]hydrogentetraphosphanide backbone, 2. MO analysis can rationalize the extreme endo/exo effect (Δδ31P = 455 ppm) on the chemical shift in the exocyclic PH group of 3. The lowest energy geometry of the anion 3 has Erel of 31 kJ mol-1 relative to 1. The most favored 3 + Na+ structure is only 15 kJ mol-1 above the lowest energy HP4Na minimum, 2 + Na+ with Na+ in endo and H in exo orientation of the bicyclo-P4 framework (Erel of 1 + Na+ is 13 kJ mol-1). In most HP4Na structures the Na+ changes the 31P NMR chemical shifts towards higher field with respect to the bare anions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089400060289
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  • 2
    Electronic Resource
    Electronic Resource
    A Density Functional Study of the Dimerization of Phosphaalkynes in the Presence of Transition Metal Fragments (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1281-1289 
    Details
    ISSN: 1434-1948
    Keywords: Phosphaalkynes ; Dimerization mechanism ; Diphosphacyclobutenes ; Density functional theory ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimerization of phosphaalkynes (R-C≡P, R = H, Me, tBu) without and with the presence of transition metal fragments, including CpCo (Cp = cyclopentadienyl) and COT-Ti (COT = cyclooctatetraene), has been probed using density functional theory calculations (B3LYP with different basis sets). MP2 and CCSD(T) calculations were also performed for the [H2C2P2] systems. In an attempt to address the exciting controversy and uncertainty about phosphaalkyne dimerization, a number of dimer formation mechanisms proposed in the literature have been examined. Some new and plausible intermediates have also been identified.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Phosphinidene Transition Metal Complexes: A Combined Ab Initio MO-DFT Study of Cr(CO)5-PR (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 107-115 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Density functional calculations ; Phosphinidene ; Carbonyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio MO and DFT calculations have been performed on phosphinidene complexes of the type Cr(CO)5-PR, with R = H, CH3, SiH3, NH2, PH2, OH, and SH. The formation of the Cr-P bond essentially arises from a ligand-to-metal charge transfer. While a significant π backdonation is also observed for the Cr(CO)5-PH, Cr(CO)5-PCH3, and Cr(CO)5-PSiH3 complexes, this is less the case for Cr(CO)5-POH, Cr(CO)5-PSH, and Cr(CO)5-PNH2, and the backbonding almost disappears for Cr(CO)5-PPH2. In both the lowest lying singlet and triplet states, all complexes exhibit a staggered conformation. CASSCF/CASPT2 calculations performed with the ANO basis sets indicate a closed-shell singlet ground state along the whole series. The binding energy between Cr(CO)5 and PR ranges from 216 kJ/mol for Cr(CO)5-PNH2 to 127 kJ/mol for Cr(CO)5-PSiH3 (B3LYP values). In general, the B3LYP-DFT scheme yields reasonable qualitative and quantitative results when compared with CASPT2(12/12).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Kann 1,2,3-Oxadiazol beständig sein?Diese Arbeit wurde vom Department of Education (Irish Government) unterstützt. (1985)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 97 (1985), S. 704-705 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19850970821
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  • 5
    Electronic Resource
    Electronic Resource
    Can 1,2,3-Oxadiazole be Stable?M. T. N. and A. F. H. thank the Department of Education (Irish Government) for financial support. (1985)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 713-715 
    Details
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198507131
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