Trinuclear Silver(I) Complexes of Fluorinated Pyrazolates

Abstract

Silver pyrazolates {[3-(CF₃)Pz]Ag}₃, {[3-(CF₃),5-(CH₃)Pz]Ag}₃, {[3-(CF₃),5-(Ph)Pz]Ag}₃, {[3-(CF₃),5-(Bu^t)Pz]Ag}₃, and {[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃ have been synthesized by treatment of the corresponding pyrazole with a slight molar excess of silver(I) oxide. This economical and convenient route gives silver pyrazolates in high (>80%) yields. X-ray crystal structures of {[3-(CF₃),5-(CH₃)Pz]Ag}₃, {[3-(CF₃),5-(Bu^t)Pz]Ag}₃, and {[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃ show that these molecules have trinuclear structures with essentially planar to highly distorted Ag₃N₆ metallacycles. {[3-(CF₃),5-(CH₃)Pz]Ag}₃ forms extended columns via intertrimer argentophilic contacts (the closest Ag···Ag separation between the neighboring trimers are 3.355 and 3.426 Å). The trinuclear {[3-(CF₃),5-(Bu^t)Pz]Ag}₃ units crystallize in pairs, basically forming “dimers of trimers”, with the six silver atom core of the adjacent trimers adopting a chair conformation. However, in these dimers of trimers, even the shortest intertrimer Ag···Ag distance (3.480 Å) is slightly longer than the van der Waals contact of silver (3.44 Å). {[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃, which has two bulky groups on each pyrazolyl ring, shows no close intertrimer Ag···Ag contacts (closest intertrimer Ag···Ag distance = 5.376 Å). The Ag−N bond distances and the intratrimer Ag···Ag separations of the silver pyrazolates do not show much variation. However, their N−Ag−N angles are sensitive to the nature (especially, the size) of substituents on the pyrazolyl rings. The π-acidic {[3,5-(CF₃)₂Pz]Ag}₃ and {[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃ form adducts with the π-base toluene. X-ray data show that they adopt extended columnar structures of the type {[Ag ₃ ] ₂·[toluene]}_∞ and {[Ag ₃ ]‘·[toluene]}_∞ ({[3,5-(CF₃)₂Pz]Ag}₃ = [Ag ₃ ],{[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃ = [Ag ₃ ]‘), in which toluene interleaves and makes face-to-face contacts with {[3-(C₃F₇),5-(Bu^t)Pz]Ag}₃ or dimers of {[3,5-(CF₃)₂Pz]Ag}₃.