Abstract
Two types of new bis-Pd(II) hexaphyrin π-ruthenium complexes are reported. A double-decker bis-Pd(II) hexaphyrin π-ruthenium complex 4 was obtained by oxidation-induced detachment of a ruthenoarene unit from the triple-decker complex 3 and oxygen-inserted triple-decker bis-Pd(II) hexaphyrin π-ruthenium complex 6 was obtained upon treatment of bis-Pd(II) [26]hexaphyrin 5 with [RuCl2(p-cymene)]2 under aerobic conditions. Although π-metal complexation of porphyrinoids often results in decreased global aromaticity due to the enhancement of local 6π aromatic segments, distinct aromatic characters were indicated for 4 and 6 by 1H-NMR spectral and theoretical calculations. These results are accounted for in terms of possible resonance contributors of hexaphyrin di- and tetraanion ligands. Thus, π-metal coordination has been shown to be effective for modulation of the overall aromaticity.
Highlights
Expanded porphyrins which consist of more than four pyrrole units and methine carbons, have been attracting continuous attention due to their intriguing optical and electrochemical properties, structural diversities, and rich coordination abilities [1,2,3,4,5,6,7]
We report a new π-metal coordination type, wherein a (p-cymene)RuII fragment is η5 -coordinated at the side pyrrole of bis-Au(III) [28]hexaphyrin, forming double-decker π-ruthenium complexes 1 and 2 (Figure 1) [8]
Π-metal complexes of porphyrinoids have been limited to those based on porphyrin, porphycene, subphthalocyanine, and subporphyrazine scaffolds [9,10,11,12,13,14,15,16], and no examples had been reported for expanded porphyrin π-metal complexes before our report [8]
Summary
Expanded porphyrins which consist of more than four pyrrole units and methine carbons, have been attracting continuous attention due to their intriguing optical and electrochemical properties, structural diversities, and rich coordination abilities [1,2,3,4,5,6,7]. Complexes 1 and 2 showed attenuated macrocyclic paratropic ring currents, probably due to the coordination-induced attenuation of the global conjugation circuit, while complex 3 showed distinct 26π aromaticity. This difference suggested that the balance between macrocyclic aromaticity (i.e., 26/28π) and local aromaticity (i.e., 6π) is important and can be modulated by metal π-complexation [17]. We report double-decker bis-Pd(II)[26]hexaphyrin π-ruthenium complex 4 and oxygen-inserted triple-decker bis-Pd(II) [26]hexaphyrin 6 Both complexes show a distinct diatropic ring current
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