Structure and reactivity of biomimetic iron-centered 2D materials from ultra-high vacuum to near-ambient pressure

It is curious how life can seem obvious, and how easily we take it for granted, while billions of complex biological processes unfold every second within and around us. From plants capturing sunlight and converting it into chemical energy while releasing oxygen into the atmosphere, to microorganisms in the soil performing, under ambient conditions, one of the most challenging chemical reactions known to humankind: the conversion of dinitrogen gas into ammonia. Many of them are catalyzed by metalloproteins whose reactive centers consist of an isolated metal atom embedded in tetrapyrrolic macrocycles, such as porphyrins. The exceptional selectivity and efficiency of these natural systems have inspired biomimetic approaches to stabilize single metal atoms in well-defined coordination environments for heterogeneous catalysis. In this context, 2D metalorganic architectures based on metalated porphyrins represent a promising platform, as they can self-assemble on suitable supports where the intrinsic properties of the metal center can be tuned through surface trans-effect and lateral coordination. This thesis investigates the structural, electronic and reactive properties of mono- and bi-metallic porphyrin-based layers and networks under UHV and NAP conditions, with a focus on the interaction with CO and O2. Two porphyrins featuring the same Fe-based macrocycle but distinct peripheral functionalization residues were selected as molecular building blocks: FeTPyP deposited on Gr/Ir(111), and hemin deposited on Au(111). In both systems, cobalt atoms were introduced as a second metal to generate bimetallic structures. Structural characterization was performed by STM, complemented, depending on the system, by NAP-XPS, IR-Vis SFG, NEXAFS spectroscopies and DFT calculations. FeTPyP molecules self-assemble into a close-packed structure with Fe in +2 oxidation state. Upon Co post-deposition, the molecular layer undergoes a complete structural reorganization, yielding a bimetallic network in which Co atoms coordinate to the pyridinic termination. This restructuring is accompanied by a significant electronic rearrangement: Co is stabilized in the +1 oxidation state, while the central Fe gets unexpectedly reduced to Fe(I), a highly reactive species capable of activating O₂ even under UHV conditions at room temperature. While Fe in the monometallic system is inert toward CO and O2, Co addition induces an electronic reorganization that activates Fe, leading both metals to participate in the reactions. CO adsorption was probed as a function of Co loading, revealing site-dependent cooperativity and changes in adsorption energies, while O₂ exposure yields ligation and activation at both metal centers, highlighting the potential applicative approaches of such monophasic bifunctional catalysts. Hemin on Au(111) forms a close-packed structure composed of both Fe-free and Fe-filled (heme) units, limited by the purity of the biological precursor. The molecules lie flat, with peripheral carboxyl groups tilted with respect to the macrocycle plane and, in some cases, overlapping the macrocycle of neighboring molecules. While CO shows negligible interaction with this system, O₂ is stabilized at the Fe centers by the additional coordination offered by the nearby carboxyl groups, mimicking the distal histidine in oxyhemoglobin and oxymioglobin, effectively reproducing the second coordination sphere observed in biological environments. To fill the vacant centers, Co was deposited onto the monolayer. Rather than simply occupying the empty sites, Co induces trans-metalation, also producing intermediate states in which both Co and Fe are present within the macrocycles. Upon O2 exposure, dioxygen activation takes place, further promoting trans-metalation. Overall, this work demonstrates that variations in peripheral functional groups strongly influence lateral coordination and reactivity in bio-inspired heterogeneous catalysts. ​