Cis-dicarbonyl binding at cobalt and iron porphyrins with saddle-shape conformation

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Diatomic molecules attached to complexed iron or cobalt centres are important in many biological processes. In natural systems, metallotetrapyrrole units carry respiratory gases or provide sensing and catalytic functions. Conceiving synthetic model systems strongly helps to determine the pertinent chemical foundations for such processes, with recent work highlighting the importance of the prosthetic groups' conformational flexibility as an intricate variable affecting their functional properties. Here, we present simple model systems to investigate, at the single molecule level, the interaction of carbon monoxide with saddle-shaped iron– and cobalt–porphyrin conformers, which have been stabilized as two-dimensional arrays on well-defined surfaces. Using scanning tunnelling microscopy we identified a novel bonding scheme expressed in tilted monocarbonyl and cis-dicarbonyl configurations at the functional metal-macrocycle unit. Modelling with density functional theory revealed that the weakly bonded diatomic carbonyl adduct can effectively bridge specific pyrrole groups with the metal atom as a result of the pronounced saddle-shape conformation of the porphyrin cage.

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Figure 1: Saddle-shape conformation of CoTPP on Ag(111) and response towards CO exposure.
Figure 2: Transfer of carbonyl ligands by molecular manipulation.
Figure 3: Comparison of experimental data and theoretical description.
Figure 4: Electronic properties of the bridged carbonyl complexes.


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This work was supported by the European Research Council Advanced Grant MolArt (no. 247299), the Deutsche Forschungsgemeinschaft Cluster of Excellence Munich Center for Advanced Photonics, Canadian National Science and Engineering Research Council (NSERC) and Canada Foundation for Innovation (CFI). W.A., A.W.-B. and J.R. thank the Technische Universität München Institute for Advanced Studies, the German Academic Exchange Service and the Deutsche Forschungsgesellschaft for scholarships, respectively. M.–L.B. acknowledges computational time at the Leibniz Rechenzentrum Garching. N.L. thanks Spanish Ministerio de Ciencia e Innovación for financial support (grant no. FIS2009-1271-C04-01).

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K.S., W.A., A.W.-B. and J.R. performed the STM experiments, and analysed and interpreted the experimental data. The theoretical analysis was provided by M.-L.B. and N.L. J.V.B., W.A. and M.-L.B. conceived the studies and co-wrote the paper with K.S. and N.L.

Correspondence to Johannes V. Barth.

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Seufert, K., Bocquet, M., Auwärter, W. et al. Cis-dicarbonyl binding at cobalt and iron porphyrins with saddle-shape conformation. Nature Chem 3, 114–119 (2011) doi:10.1038/nchem.956

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