Structural Variations in Tetrasilver(I) Complexes of Pyrazolate-bridged Compartmental N-Heterocyclic Carbene Ligands

Abstract

A set of pyrazole-bridged bis(imidazolium) compounds [H(3)L(1)]X(2) - [H(3)L(4)]X(2) (L(1) = 3,5-bis[1-(tert-butyl)imidazolium-1-ylmethyl]-1H-pyrazole; L(2) = 3,5-bis[1-(tert-butyl)imidazolium-1-ylmethyl]-4-phenyl-1H-pyrazole; L(3) = 3,5-bis[1-(1-adamantyl)imidazolium-1-ylmethyl]-1H-pyrazole; L(4) = 3,5-bis[1-(1-adamantyl)imidazolium-1-ylmethyl]-4-phenyl-1H-pyrazole; X = Cl(-). BF(4)(-) or PF(6)(-)) has been prepared, and three compounds have been characterized by X-ray crystallography. The unique [H(3)L(4)]H(2)L(4)(3) features a dimeric face-to-face arrangement of two molecules due to the involvement of both the pyrazole-NH and the imidazolium C(2)H in hydrogen bonding. [H(3)L(1)]X(2) - [H(3)L(4)]X(2) serve as precursors for silver(I) complexes with compartmental pyrazolate-bridged bis(NHC) ligands. The complexes have been readily prepared by the Ag(2)O route and feature either the known (L(1-4))(2)Ag(4) or the new (H(2)L(1))(4)Ag(4) motif, depending on the solvent for the reaction (MeCN or acetone). (H(2)L(1))(4)Ag(4)(8) contains a central (pzAg)(4) ring with pendant imidazolium side arms. Upon further reaction with Ag(2)O in MeCN it was found to undergo transformation to the corresponding (L(1))(2)Ag(4)(2). All complexes have been thoroughly studied by NMR spectroscopy in solution, and preliminary luminescence data of (H(2)L(1))(4)Ag(4)(8) have been recorded.