Multinuclear NMR solution studies on complexes of hexakis(pyrazol-1-yl)benzene (hpzb) with Ag(I)

Abstract The reaction of the polydentate N-donor ligand hexakis(pyrazol-1-yl)benzene (hpzb) with AgSbF 6 /PPh 3 or AgClO 4 PPh 3 in a 1:1 ratio leads to the complexes [Ag(PPh 3 )(hpzb)]SbF 6 ( 1 ) or [Ag(PPh 3 )(hpzb)]ClO 4 ( 3 ). When two or three equivalents of the silver derivatives are used the species [Ag(PPh 3 ) 2 ]X are formed in addition to 1 or 3 . In the case of SbF 6 − the remaining Ag + competes with AgPPh 3 + for coordination to hpzb and the derivative [Ag(hpzb)]SbF 6 ( 2 ) is also obtained, while in the case of ClO 4 − the insoluble salt AgClO 4 is formed. The same reactions performed with hpzb– 15 N 12 confirmed the presence of the N-donor ligand in 1 – 3 . At room temperature a Ag–P dissociation process is observed for all the derivatives containing Ag–PPh 3 fragments. Complexes 1 – 3 show in solution an intramolecular argentotropic shift that makes the six pyrazolyl rings of the hpzb ligand equivalent on the 1 H NMR time scale. When the amount of counteranion present in solution is sufficiently high, an intermediate of lower coordination number (stabilized with the anion) is observed for complexes 1 and 3 in the low temperature 31 P NMR spectra in addition to the three-coordinated species. This intermediate is more stable in the case of ClO 4 − due to the higher coordinating ability of this anion.