Group-IVb Porphyrins

If Sn11 salts are reacted with porphyrins one usually obtains SnIV porphyrins, but in rigorously dried and degassed pyridine another complex is obtained with a Soret band close to 460 nm [Whitten (203)]. This could not be demetalated, neither could the metal be exchanged with copper salts. The latter treatment results, however, in formation of SnIV porphyrins. Reduction of SnIV porphyrins with sodium boro-hydride leads to tin porphyrins which can be demetalated by hydrochloric acid, but no 460 nm band is found in the reaction mixture [Fuhrhop (75)]. Thus, the properties of Sn11 porphyrins remain unconfirmed. 

These metalloporphyrins are extremely acid-stable and produce a normal electronic spectrum [Snlv OEP (OAc)2 576 (19,100) 538 (19,100) 411 (403,000)] [Parnemann (139)]. The electrochemical redox pattern probably does not involve a SnIV Sn11 reduction. It follows that the porphyrin ligand is reduced, not the SnIV central ion [Fuhrhop (74)]. 

These metalloporphyrins are extremely acid-labile and produce the typical lead-porphyrin electronic spectrum with a Soret band close to 470 nm (see text relating to Fig. 1). 

A complex has been obtained by electrochemical oxidation of the Pb11 complexes. This oxidation is the only case where the porphyrin ligand is first oxidized to a cation radical, which then on further oxidation converts to the porphyrin with a four-valent central ion -e -e 

PbIV porphyrins are also formed on chemical oxidation, have a normal electronic spectrum (577, 538, 409) and are extremely unstable [Fuhrhop 

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