Metallocycle and ring-opening polymerization of silver(I) complexes with 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)benzene ligand

The reaction of 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)benzene (bib) ligand with silver(I) nitrate in a 1:1 molar ratio generated a [2 + 2] metallocyclic complex [Ag2(bib)2](NO3)2 · 2H2O, in which bib ligand displayed in cis   configuration. When the additional competing ligands/counterions, such as oxlate salt, 1,2-diaminoethene (en), 1,3-diaminopropane (pn), NO2- and VO3- were introduced, respectively, to the above-mentioned reaction solution, ring-open polymerization of sliver(I) complexes {[Ag(bib)]NO3 · H2O}n (1), {[Ag(bib)2]X}n (X=NO3- (2), ClO4- (3)), {[Ag2(bib)2(NO2)](NO2) · 19/8H2O}n (4) and {[Ag2(bib)2](V4O12)0.5 · 3H2O · 2MeCN}n (5) were generated. In compounds 1, 4 and 5, bib ligand adopts trans configuration and twists around the Ag–Ag axis, giving rise to single-stranded helical structure with short adjacent Ag⋯Ag distances of 3.56, 3.56, 3.50 and 3.63 Å, respectively. Compounds 2 and 3 are 1D coordination polymers fusing the [2 + 2] metallocycle [Ag2(bib)2]2+, in which bib ligand exhibits in cis configuration and the metallocycles have longer Ag⋯Ag distances of 8.52 Å in 2 and 8.61 Å in 3 along with the strong intracyclicπ–π interactions between phenyl groups. Cis and trans configurations of bib coexist in solution and crystallize in complexes 1 and 2 in the solid state in the presence of en or pn. The solution of 1 and 2 can be converted into 3 via the addition of the bulky ClO4- counter anion or into 4 through introduction of the competing ligand/conuterion NO2-.

Both cis and trans configurations of bib ligand were observed in Ag(I)–bib complexes, they coexisted and led to the formations of polymers rather than discrete metallocycle in the presence of competing ligands/counterions.Figure optionsDownload as PowerPoint slide