The Role of Weak Interactions in Strong Intermolecular M···Cl Complexes of Coinage Metal Pyrazolates: Spectroscopic and DFT Study

The nondestructive reversible complexation of the macrocyclic group 11 metal pyrazolates {[3,5-(CF3)2Pz]M}3 (M = Cu(I), Ag(I)) to the halogen atom X = Cl, Br of η3-allyliron tricarbonyl halides (η3-2-R-C3H4)Fe(CO)3X is revealed by the variable-temperature spectroscopic (IR, NMR) study combined with density functional theory calculations. The composition of all complexes at room temperature is determined as 1:1. In the case of the [AgL]3 macrocycle, complexes 1:2 are observed at low temperature (<260 K). The complex's stability depends on the substituents in the allyl fragment and halide ligand as well as on the metal atom (Ag(I), Cu(I)) in the macrocycle. For bulky substituents (Me and Ph) the endo/exo equilibrium of the parent (η3-2-R-C3H4)Fe(CO)3X shifts upon the complex formation in favor of the exo isomer due to additional noncovalent interactions of the substituent with macrocycle. © 2016 American Chemical Society.