Synthesis, structure, electrochemistry, and spectroelectrochemistry of hypervalent Phosphorus(V) octaethylporphyrins and theoretical analysis of the nature of the PO bond in P(OEP)(CH2CH3)(O)

A variety of phosphorus(V) octaethylporphyrin derivatives of the type [P(OE P)(X)(Y)](+)Z(-) (OEP: octaethylporphyrin) (X = CH3, CH2CH3, C6H5, F; Y = C H3, 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 c ompounds reveals that the degree of ruffling of the porphyrin core becomes greater and the average P-N bond distance becomes shorter as the axial liga nds become more electronegative. Therefore, the electronic effect of the ax ial substituents plays a major role in determining the degree of ruffling a lthough the steric effect of the substituents plays some role, A comparison of the H-1 NMR chemical shifts for the series of [P(OEP)(CH2CH3)(Y)](+)Z(- ) complexes with those of the corresponding arsenic porphyrins, which posse ss a planar core, indicates a much smaller ring current effect of the porph yrin core in the severely ruffled phosphorus porphyrins. The electrochemist ry, spectroelectrochemistry and ESR spectroscopy of the singly reduced comp ounds 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 ana lysis of P(OEP)(CH2CH3)(O) reveals that the PO bond length is very short (1 .475(7) Angstrom) and is comparable to that in triphenylphosphine oxide (1. 483 Angstrom). The features of the quite unique hexacoordinate hypervalent compounds are investigated by density functional calculation of a model (Po r)P(CH2CH3)(O) and (Por)P(F)(O) (Por: unsubstituted porphyrin).