The chemistry of Group 15 element porphyrins bearing element–carbon bonds: synthesis and properties

A variety of Group 15 element porphyrins bearing element–carbon bond(s) were synthesized mainly by use of R3Al as an alkylating reagent. The synthetic methods, X-ray crystallographic structures, some spectral data (1H-NMR), and some reactions of the porphyrins were surveyed. One of the most important properties of these compounds is the formation of the element–oxygen double bond in the phosphorus and arsenic porphyrins. The bond formation was confirmed by X-ray crystallographic analysis of (OEP)P(Et)(O). The PO bond length of [(OEP)P(Et)(OH)]+Cl− and (OEP)P(Et)(O) was 1.636(4) and 1.484(9) Å, respectively (cf. PO bond length of Ph3PO is 1.483 Å). Since (OEP)P(Et)(O) was stabilized by the formation of the PO bond, the OH proton of [(OEP)PEt(OH)]+Cl− was acidic (pKa ca. 7–8). Although the similar formation of the double bond was not observed in the corresponding antimony compounds, the corresponding AsO formation was observed in newly synthesized (OEP)As(R)(O). The relatively high acidity of the OH protons in [(OEP)M(R)(OH)]+X− (M=P, As) {and the stability of the (OEP)M(R)(O)} would be the main reason for the relatively high reactivity of phosphorus and arsenic porphyrins, [(OEP)M(R)(OH)]+X−, toward (OEP)Al(Me) to give μ-oxobridged dinuclear porphyrins and the high reactivity of phosphorus and arsenic porphyrins bearing a OOH group toward triphenylphosphine. In addition, X-ray analysis of a variety of phosphorus(V), arsenic(V), antimony(V) octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) derivatives showed the effect of the axial ligand(s) on the distortion of the porphyrin core from the plane.