& Materials Chemistry Water Formation for the Metalation of Porphyrin Molecules on Oxidized Cu(111) Alberto Verdini, [b] Prasha Shinde, [e] Gian Luca Montanari, [c] Simone Tommaso Suran-Brunelli, [a] Marco Caputo, [d] Giovanni Di Santo, [a] Carlo A. Pignedoli, [e] Luca Floreano, [b] Daniele Passerone, [e] and Andrea Goldoni* [a] Abstract: Herein the formation of water molecules in the in- termediate step of the redox reaction of porphyrins self-met- alation on O/Cu(111) is demonstrated. Photoemission meas- urements show that the temperature on which porphyrins pick-up a substrate metal atom on O/Cu(111) is reduced by about 185  15 K with respect to the pure Cu(111). DFT cal- culations clearly indicate that the formation of a water mole- cule is less expensive than the formation of H 2 on the O/ Cu(111) substrate and, in some cases, it can be also exother- mic. Finding the means for the creation of ordered systems on a nanometric scale of metalloporphyrins, in particular those not available in nature or difficult to obtain by simple chemical solution reactions, represents one of the challenges of the cur- rent scientific research on metal–organic molecules. This is be- cause metalloporphyrins are involved in many natural process- es with the role of catalyst, absorber, releaser and carrier of gases, sunlight harvester, etc. [1–6] New metalloporphyrins, espe- cially ordered, can offer novel and interesting playgrounds with properties not yet exploited, such as in magnetic sys- tems. [7, 8] Recently, the vacuum metalation of porphyrins (or in general of tetrapyrrole-based molecules) provided complex nanostruc- tures and unattainable materials through conventional synthet- ic protocols, while sharing the main features common to the redox reaction occurring in solutions and even the same bio- synthetic pathways. The main sequence of the involved redox reaction includes the supply of the metal ion, the coordination of the metal ion with the nitrogen atoms of the macrocycle with the given molecular valence state, and the deprotonation of the basic macrocycle. [9] In order to coordinate such a process in an exothermic way, a relevant role is played by an „inter- mediate reaction“ step in which the metal center forms a bond with the macrocycle and, at the same time, participates in the fabrication of a hydrogen molecule with the two not yet re- leased hydrogen atoms coming from the center of the macro- cycle (sitting-atop the molecule). DFT calculations in the gas phase identify the transfer of the first hydrogen atom to the metal center as being the main barrier to overcome. [9] In any case, the metalation should also be influenced by de- formations of the macrocycle ring. The substrate can easily lead to macrocycle deformations and it can catalyze the metal- ation reaction, mimicking the role of the proteins in the bio- synthesis. Finally, another benefit of the vacuum route for met- alloporphyrin formations is the solvent-free environment. We can discriminate three vacuum metalation methods for growing a porphyrin monolayer on surfaces, namely metal physical vapor deposition, [9–21] substrate self-metalation, [22–31] and alternative routes based on the copresence of thermally unstable metal–organic molecules. [32, 33] Among the three meth- ods, which of course have advantages and disadvantages, self- metalation allows the use of only the free-base porphyrins without any other reactant. At the moment, of course, this method cannot be used to create heterostructures and the range of suitable substrates is small. A new method based on oxidation of substrate surfaces has been reported by Nowakowski et al., [28] showing that surface adsorption of oxygen on Cu(100) enables full self-metalation of 2H-tetraphenyl-porphyrin at about room temperature, that is lower by about 200 K than the temperature at which a full metalation was observed on the Cu(100) surface. [24, 28] Herein we show that this is also true for the more-stable Cu(111) for both 5,10,15,20-tetraphenyl-21H,23H-porphyrin (2H-TPP) and meso-tetra-(3,5-di-tert-butylphenyl)porphyrin (2H-TBPP), with the evidence that the redox reaction is related to the forma- tion of water molecules instead of H 2 formation [a] Dr. S. T. Suran-Brunelli, Dr. G. Di Santo, Dr. A. Goldoni Elettra Sincrotrone Trieste s.s. 14 km 163.5 in Area Science Park, 34149 Trieste (Italy) E-mail : goldonia@elettra.eu [b] Dr. A. Verdini, Dr. L. Floreano Istituto Officina dei Materiali—CNR, Laboratorio TASC s.s. 14 km 163.5, 34149 Trieste (Italy) [c] Dr. G. L. Montanari Dipartimento di Fisica, Università di Trieste via A. Valerio 2, 34100 Trieste (Italy) [d] Dr. M. Caputo Laboratoire de Physique des Solides, CNRS-UMR 8502 Universit Paris-Sud, 91405 Orsay (France) [e] Dr. P. Shinde, Dr. C. A. Pignedoli, Prof. D. Passerone Empa, Swiss Federal Laboratories for Materials Science and Technology Nanotech@surfaces Laboratory Ueberlandstrasse 129, 8600 Dübendorf (Switzerland) Chem. Eur. J. 2016, 22,1–7  2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 && These are not the final page numbers! ÞÞ Full Paper DOI: 10.1002/chem.201602105