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Download fileSynthesis, Structure, Electrochemistry, and Spectroelectrochemistry of Hypervalent Phosphorus(V) Octaethylporphyrins and Theoretical Analysis of the Nature of the PO Bond in P(OEP)(CH2CH3)(O)
journal contribution
posted on 2001-09-25, 00:00 authored by Kin-ya Akiba, Ryo Nadano, Wataru Satoh, Yohsuke Yamamoto, Shigeru Nagase, Zhongping Ou, Xiaoyu Tan, Karl M. KadishA variety of phosphorus(V) octaethylporphyrin derivatives of the type [P(OEP)(X)(Y)]+Z- (OEP: octaethylporphyrin) (X = CH3, CH2CH3, C6H5, F; Y = CH3, CH2CH3, OH, OCH3, OCH2CH3, On-Pr, Oi-Pr, Osec-Bu, NHBu,
NEt2, Cl, F, O-; Z = ClO4, PF6) were prepared. X-ray crystallographic analysis of eleven compounds reveals
that the degree of ruffling of the porphyrin core becomes greater and the average P−N bond distance becomes
shorter as the axial ligands become more electronegative. Therefore, the electronic effect of the axial substituents
plays a major role in determining the degree of ruffling although the steric effect of the substituents plays some
role. A comparison of the 1H NMR chemical shifts for the series of [P(OEP)(CH2CH3)(Y)]+Z- complexes with
those of the corresponding arsenic porphyrins, which possess a planar core, indicates a much smaller ring current
effect of the porphyrin core in the severely ruffled phosphorus porphyrins. The electrochemistry, spectroelectrochemistry and ESR spectroscopy of the singly reduced compounds are also discussed. The OH protons of [P(OEP)(X)(OH)]+ are acidic enough to generate P(OEP)(X)(O) by treatment with aq dilute NaOH. X-ray analysis of
P(OEP)(CH2CH3)(O) reveals that the PO bond length is very short (1.475(7) Å) and is comparable to that in
triphenylphosphine oxide (1.483 Å). The features of the quite unique hexacoordinate hypervalent compounds are
investigated by density functional calculation of a model (Por)P(CH2CH3)(O) and (Por)P(F)(O) (Por: unsubstituted
porphyrin).