Tuning the Bonding of a μ-Mesityl Ligand on Dicopper(I) through a Proton-Responsive Expanded PNNP Pincer Ligand

We report the synthesis and characterization of a series of cationic, neutral and anionic dicopper(I) complexes featuring a µ-mesityl ligand and a naphthyridine-derived PNNP expanded pincer ligand. Structural characterization showed that the protonation state of the dinucleating ligand has a pronounced effect on the bending and tilting of the µ-mesityl ligand. DFT calculations indicate that the varying orientations of the µ-mesityl ligand are inherent due to changes in electronic structure rather than crystal packing effects. NBO analysis reveals how the interactions that contribute to the 3-center 2-electron bond between the µ-mesityl ligand and the dicopper core change for the various degrees of observed bending and tilting.