Sitting-a-top

Proton NMR spectral analysis of the protonated complexes 5.89-5.91 revealed highly unsymmetrical structures, each of which appeared (on the basis of integration studies) to contain three internal NH protons. For these reasons, a sitting-a-top structure was proposed for these complexes. Subsequently, the out-of-plane metal ligation that these structures required was confirmed via a single crystal X-ray diffraction study of complex 5.90. The resulting structure is shown in Figure 5.5.3. ... 

Perhaps as a consequence of Johnson s failure, 20 years elapsed before Sessler and coworkers reported that certain p -type complexes could in fact be formed with heterosapphyrins.These latter workers were clearly inspired by their earlier successful syntheses of p -type rhodium(I) and iridium(I) carbonyl complexes of pentaazasapphyrins 5.21 and 5.23 vide supra). Thus, in a first experiment, they treated the monothiasapphyrin 5.71 with Rli2(CO)4Cl2 (Scheme 5.5.4). This afforded the structurally characterized [Rh(CO)2]2 monothiasapphyrin complex 5.100 (Figure 5.5.6). Subsequently, they prepared the bis-iridium complex 5.101 of the mono-selenasapphyrin 5.73. This complex was also characterized by X-ray diffraction analysis. The resulting structure then served to confirm the expected sitting-a-top binding mode (Figure 5.5.7). 

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