(Isocyano Group π-Hole)⋅⋅⋅[d z 2 -MII ] Interactions of (Isocyanide)[MII ] Complexes, in which Positively Charged Metal Centers (d8 -M=Pt, Pd) Act as Nucleophiles

Abstract

Inspection of the X-ray structures of the newly prepared trans-[M^II (CNXyl)₂ (DAPT)₂ ]Cl(BF₄ ) (M=Pd, Pt; Xyl=2,6-Me₂ C₆ H₃ ; DAPT=4,6-diaminopyrimidine-2(1H)-thione) complexes and the appropriate Hirshfeld molecular surface analysis allowed the recognition of the previously unknown π-hole⋅⋅⋅metal interactions between a ligated isocyano group (acting as a π-hole donor) and the positively charged d⁸ -Pt^II and d⁸ -Pd^II metal centers (acting as nucleophiles); this is the first identification of π-hole⋅⋅⋅metal interactions with triple-bond species. Results of DFT calculations followed by the topological analysis of the electron density distribution within the framework of Bader's theory (quantum theory of atoms in molecules, QTAIM) confirmed the presence of these contacts. The electrostatic surface potential calculations indicated that π-hole⋅⋅⋅metal contacts are formed upon interaction between the electrophilic isocyano C atom (π-hole donor) and the nucleophilic d ${}_{z{}^2}$ orbital of the metal centers, which act as π-hole acceptors. Available CCDC data were processed from the perspective of the π-hole⋅⋅⋅metal interactions with isocyanide ligands, and their analysis disclosed the role of metal nucleophilicity in the corresponding π-hole acceptor ability.

Keywords: QTAIM calculations; density functional calculations; isocyanide ligands; metal interactions; noncovalent interactions.