Owing to the central importance of multiporphyrin assemblies in photosynthetic reaction centers and light-harvesting antenna complexes, considerable attention has been focused on the development of covalently linked porphyrin arrays as effective biomimetic models. Systematic studies on these models will aid also in the development of new photonic materials and molecular devices.[' In these model studies a variety of bridges that connect porphyrin chromophores have been examined in their abilities to facilitate electron and photon connectivity or to perturb the spectral properties of the porphyrin chromophores. As an extension. a bridgeless, directly coupled porphyrin array may be a fascinating. ultimate candidate for exploring novel connectivi ty.Here we report on a novel, very facile oxidative coupling reaction of zinc(1r) 5,15-di(3,5-di-tert-butylphenyl)porphyrin (1) to give porphyrin dimer 2 and porphyrin trimer 3 as the first example of meso,meso-coupled multiporphyrins. Treatment of a chloroform solution of 1 with AgPF, (0.5 equiv) dissolved in acetonitrile for 5 h gave 2 and 3; NMR analysis revealed the distribution of products: 1 (47%), 2 (27%), and 3 (4%). Although these products were difficult to separate over standard silica gel columns, they were separated by size exclusion chrom a t~g r a p h y ,~~] by which the products are eluted in the order of molecular weight: first, higher oligomers and trace amounts of tetramer 4 > 3 > 2 > 1. The yields of isolated compounds were 25% for 2 and 4 % for 3, based on the amount of 1 used.Reaction of 2 under analogous conditions (0.5 equiv AgPF,) gave 4 in 23% yield. The regioselectivty of the coupling was quite high.'']Compounds 2-4 were fully characterized by 'H NMR spectroscopy (500 MHz) and FAB mass spectrometry. 'HNMR analysis revealed the presence of one meso-and two, four, six, and eight &protons in 1-4, respectively (Scheme 1). In the spec-1 2 9.20 8.72 8.l7 8.29 n m I r kr 3 8.84 9.21 Ar Ar 4 Ar 5 Scheme 1. Structures of 1-5. NMR chemical shifts of the mesoand fi-protons (CDCI,) are indicated. Ar = 3,5-tBu,C,H3.trum of 2 the signals of the inner P-protons are shifted upfield by A6 = 1.33 and 0.46 ppm relative to those of 1, reflecting the ring current effect of the second porphyrin ring, while the signals of the outer P-protons appear nearly at the same chemical shifts. Similar features are observed for 3 and 4. These data, analyzed in terms of the ring current model, suggest an approximate perpendicular arrangement of the neighboring porphyrins. AgCIO, and AgBF, were similarly effective in this coupling, but the use of AgNO, led to meso-nitration, giving 5 almost quantitatively. The coupling reaction was accelerated by addition of I,; under these conditions the reaction was complete within 5-10 min.['] In the I,-promoted reactions use of one or more equivalents of the Ag' salt and I, led to lower yields of 2 and 3, under otherwise the same reaction conditions."'] Most probably, the initial generation of radical cation 1" followed by nucleophilic attack by ...

Meso-meso coupled diporphyrins were prepared from 5,10,15-trisubstituted zinc-porphyrins in high yields upon treatment with AgPF6 alone or with AgPF6 and I2.

Eine starke Excitonkopplung, die zur Aufspaltung der Soret‐Bande führt, und nur geringe spektroskopische Änderungen bezüglich der Q‐Bande deuten auf die senkrechte Anordnung der beiden Porphyrinringe im Dimer 1 hin. Diese Verbindung sowie die analogen linearen Tri‐ und Tetramere entstehen durch oxidative Kupplung des entsprechenden 5,15‐Diarylporphyrins und sind die ersten Beispiele für Verbindungen mit direkt meso‐meso‐verknüpften Porphyrin‐Chromophoren. Ar = 3,5‐tBu2C6H3.

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Facile Regioselective meso-Iodination of Porphyrins.-Regioselective iodination leads to different types of porphyrins, e.g. (II), (V), and (VII). The products are interesting starting materials for the synthesis of supramolecular porphyrin models as shown by two examples. -(NAKANO,

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