From Coordination to π‐Hole Chemistry of Transition Metals: Metalloporphyrins as a Case of Study

Herein we have evidenced the formation of favorable π‐hole Br⋅⋅⋅metal noncovalent interactions (NCIs) involving elements from groups 9, 11 and 12. More in detail, M (M=Co2+, Ni2+, Cu2+ and Zn2+) containing porphyrins have been synthesized and their supramolecular assemblies structurally characterized by means of single crystal X‐ray diffraction and Hirshfeld surface analyses, revealing the formation of directional Br⋅⋅⋅M contacts in addition to ancillary hydrogen bond and lone pair‐π bonds. Computations at the PBE0‐D3/def2‐TZVP level of theory revealed the π‐hole nature of the Br⋅⋅⋅M interaction. In addition, the physical nature of these NCIs was studied using Quantum Chemistry methodologies, providing evidence of π‐hole Spodium and Regium bonds in Zn2+ and Cu2+ porphyrins, in addition to unveiling the presence of a π‐hole for group 9 (Co2+). On the other hand, group 10 (Ni2+) acted as both electron donor and acceptor moiety without showing an electropositive π‐hole. Owing to the underexplored potential of π‐hole interactions in transition metal chemistry, we believe the results reported herein will be useful in supramolecular chemistry, organometallics, and solid‐state chemistry by i) putting under the spotlight the π‐hole chemistry involving first row transition metals and ii) unlocking a new tool to direct the self‐assembly of metalloporphyrins. In this combined experimental (X‐ray structure analysis) and computational (DFT‐D3 calculations) study we have systematically evaluated the π‐hole donor ability of elements across Groups 9 to 12 using metalated porphyrins (ppys) as model systems. The results obtained will make impact in the fields supramolecular chemistry, crystal engineering and catalysis, where noncovalent Lewis Base⋅⋅⋅Metal interactions play a crucial role.