Dithiaporphyrins

The unnatural porphyrin family still fascinates the imagination. This year, to give a flavor for the diversity, there has appeared hybrid calixphyrins <00OL3103>, doubly A-confused porphyrins , unsymmetrical porphyrins attached to a modified 5,10,15,20-tetra (4-(2-trimethylsilylethynyl)phenyl]-21-23-dithiaporphyrin <00TL3709>,... 

The first example of a metal complex of the dithiaporphyrin (400) has been reported. Ligand (400) reacts with [Ru(cod)Cl2] to give tra 5-[RuCl2(400)] which has been characterized in solution using NMR spectroscopy and electrochemical methods, and in the solid state by X-ray diffraction. The latter reveals that the two thiophene rings in coordinated ligand (400) are tilted out of the mean porphyrin plane. 

Several porphyrin analogues with the pyrrolic nitrogens substituted by heteroatoms have been synthesized, but only the oxa analogues (23 X = O, Y = NH) are reported to form stable metal complexes (Figure 8). 60 Formation of a Zn complex of the thia analogue (23 X = S, Y = NH) requires the presence of a large excess of Zn" ion. An iron complex of dithiaporphyrin (23 X = Y = S) is also known. 

Ravikanth and coworkers have synthesized (S-pyrrole-substituted 21,23-dithiaporphyrins by refluxing 21,23-dithiaporphyrin with NBS in chloroform. (5-Aryl-substituted thiaporphyrin 238 (Scheme 94) has been obtained by condensing 3,4-disubstituted pyrroles 237 with thiophene diol 222 (X=S) under mild acid conditions (00CL480). 

The incorporation of cyclic substituents, such as propane-1,3-diyldioxy, its ethyl and benzyl derivatives substituted at the (1-thiophene carbons of 21,23-dithiaporphyrins 240b and 21-monothiaporphyrins 241b (Scheme 95), has also been reported (04BCJ1173) by condensing the substituted thiophene diols 239b with benzaldehyde and pyrrole. The cyclic substituents at the (5-thiophene carbon atoms alter electronic properties of porphyrin. 

A series of tetraalkoxy and dialkoxy-substituted 21,23-dithiaporphyrins 240c and 21-monothiaporphyrins 241c with methoxy, butoxy, octy-loxy, and dodecyloxy substituents at (5-thiophene carbon atoms were also synthesized (02JCS(CC)2642,04T10671). 

The front cover illustration depicts the X-ray structure of 5,10,15,2()-(4-bromophenyl)-21,23-dithiaporphyrin obtained by S. State and T. Sohnel, TU Dresden. 

Macrocycles 158 and 159 containing alternating thiophene and pyrrole rings are obtained by a Rothemund-type synthesis <2001CEJ5099>. The so-called tetrathiaoctaphyrin can be reduced to the dihydrotetrathiaoctaphyrin. Two dithiaporphyrin-like pockets behave as independent proton acceptors. Stepwise protonation leads to several cationic species. The interconversion of isomers in solution has been discussed and a new mechanism proposed. 

The 5,10,15,20-tetra(p-tolyl)-21,23-dithiaporphyrin with an inverted pyrrole ring, 5,10,15,20-tetra(p-tolyl)-2-aza-21-carba-22,24-dithiaporphyrin and 5,10,15,20-tetra(p-tolyl)-25,27-dithiasaporphyrin have been synthesized by the condensation of 2,5-bis[(p-tolyl)hydroxymethyl]thiophene and pyrrole <01OL1933> whereas, their acid condensation yield the novel heteroporphyrins 5,10,15,20,25,30,35,40-octa(p-tolyl)-41,43,45,47-tetrathia-[36]octaporphyrin( 1.1.1.1.1.1.1.1) and 5,10,15,20,5,30,35,40-octa(p-tolyl)-dihydro-... 

In the case of 21,23-dithiaporphyrin derivative 45h, opp-21,23-dithiadibenzoporphyrin opp-Alh was predominantiy formed during the fragmentation (Scheme 15.8) [31]. In the case of 21 -thiaporphyrin derivative 45g, an ethylene molecule was expelled selectively from the bicyclo[2.2.2]octadiene moiety adjacent to the thiophene part to give 21-thiabenzo [( jporphyrin 46g and then 21-thiabenzo[g,g ]porphyrin derivative opp-Alg. In these cases, the last ethylene extrusion occurred from 200 °C and proceeded very slowly [32]. 

---