Title: Calculated properties and ring-chain rearrangements of triphosphirane (P3H3)
Authors: Nguyen, Minh Tho ×
Dransfeld, A
Landuyt, L
Vanquickenborne, Luc
Schleyer, PV #
Issue Date: 2000
Series Title: European journal of inorganic chemistry issue:1 pages:103-112
Conference: date:Univ Louvain, Dept Chem, B-3001 Louvain, Belgium; Univ Erlangen Nurnberg, Inst Organ Chem, D-91054 Erlangen, Germany
Abstract: Ab initio quantum chemical calculations have been used to explore the P3H3 potential energy surface focussing on the ring-chain rearrangements of the three-membered ring in (PH)(3) (1), the parent triphosphirane. Relative energies between stationary points were estimated using the QCISD(T)/6-311G(d,p) method based on MP2/631G(d,p) geometries and corrected for zero-point contributions. Ring strain, proton affinities, ionization and excitation energies and heats of formation have been evaluated using larger basis sets, e.g. 6-311++G(3df,2p). The cyclic trans-triphosphirane (1a) is the most stable P3H3 isomer and lies about 40 kJ/mol below the open-chain phosphanyldiphosphene (H2P-P=PH). The decrease of ring strain in three-membered rings when CH2 is replaced by PH is confirmed. Triphosphirane 1a is a virtually strain-free ring and even gains some stabilization relative to three separate P-P single bonds. The reduced ring strain also helps diminish the phosphorus inversion barrier to 224 kJ/mol compared to the monocyclic isomers of (CH2)(PH)(2) and (CH2)(2)(PH) Compound la follows a pure ring-opening or a 1,2-hydrogen shift rather than a combined motion pathway, in fundamental contrast with corresponding processes of diphosphirane and phosphirane. This is due to the existence of an open-chain P3H3 phosphorane intermediate stabilized by allylic conjugation. The pericyclic ring-opening of 1a is the most favored process but the energy barrier in the gas phase is about 180 kJ/mol high. Electron density is largely delocalized within the three-membered P-3 ring not only in the C-3v-symmetric 1b (all-cis) but also in 1a (C-s). The proton affinity of 1a is similar to that of PH3. The proton affinities decrease with n in cyclo-(CH3)(3-n)(PH)(n) and their values were obtained: PA(1a) = 777 +/-10, PA(diphosphirane) = 799 +/-10 and PA(phosphirane) = 802 +/-10 kJ/mol. Heats of formation are evaluated as follows (Delta H degrees(fo) at 0 K in kJ/mol): 1a, 70 +/-10; cyclo-(PH)(2)(PH2)(+) (protonated 1a), 821 +/-10; diphosphirane, 85 +/-10; cyclo-(CH2)(PH) (PH2)(+) (protonated diphosphirane), 814 +/-10; phosphirane, 86 +/-10; and protonated phosphirane, 812 +/-10 kJ/mol. All P rings remain cyclic following ionization to the radical cations. Adiabatic ionization energies (IEa) are estimated as: la and diphosphirane, 9.3 +/-0.3 eV and phosphirane 9.5 +/-0.3 eV. The first UV absorption band shifts toward the longer wavelength region on going from phosphirane to 1a. The GIAO/B3LYP computed magnetic shieldings for la and related molecules reveal a clear relationship between the narrow bond angles in the rings and their unusually strong magnetic shielding. The similarity of the predicted P-31-NMR signals in la and its heteroanalog diphosphirane, (CH2)(PH)(2), can be rationalized in terms of a compensation of the carbon-substituent effect [downfield shift) and the bond-bending effect imposed by the ring (upfield shift).
ISSN: 1434-1948
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

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