Multinuclear NMR solution studies on complexes of hexakis(pyrazol-1-yl)benzene (hpzb) with Ag(I)
The reaction of the polydentate N-donor ligand hexakis(pyrazol-1-yl)benzene (hpzb) with AgSbF6/PPh3 or AgClO4PPh3 in a 1:1 ratio leads to the complexes [Ag(PPh3)(hpzb)]SbF6 (1) or [Ag(PPh3)(hpzb)]ClO4 (3). When two or three equivalents of the silver derivatives are used the species [Ag(PPh3)2]X are formed in addition to 1 or 3. In the case of SbF6- the remaining Ag+ competes with AgPPh3+ for coordination to hpzb and the derivative [Ag(hpzb)]SbF6 (2) is also obtained, while in the case of ClO4- the insoluble salt AgClO4 is formed. The same reactions performed with hpzb-15N12 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-PPh3 fragments. Complexes 1-3 show in solution an intramolecular argentotropic shift that makes the six pyrazolyl rings of the hpzb ligand equivalent on the 1H 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 31P NMR spectra in addition to the three-coordinated species. This intermediate is more stable in the case of ClO4- due to the higher coordinating ability of this anion.
Caballero, Agustín,Guerrero, Ana,Jalón, Félix A.,Manzano, Blanca R.,Claramunt, Rosa M.,Santa María, M. Dolores,Escolástico, Consuelo,Elguero, José
p. 168 - 174
(2008/10/08)
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