N,N,O Ligands Based on Triazoles and Transition Metal Complexes Thereof

Abstract

AbstractThe reaction of 2H‐benzotriazole (1) with dichloroacetic acid leads to the symmetric bis(2H‐benzotriazol‐2‐yl)methane (2c) in 40 % yield. Deprotonation of 2c at the bridging methylene group and subsequent carboxylation with CO2 yielded the new tripodal N,N,O ligand bis(2H‐benzotriazol‐2‐yl)acetic acid Hbbta (3). The sterically less demanding sodium 3,3‐bis(1H‐1,2,4‐triazol‐1‐yl)propionate Na[btp] (5) was obtained by saponification of methyl 3,3‐bis(1H‐1,2,4‐triazol‐1‐yl)propionate (4). The heteroscorpionate ligand 3 was treated with [MnBr(CO)5] and [RuCl2(PPh3)3] to form the manganese tricarbonyl complex [Mn(bbta)(CO)3] (6) and the air stable ruthenium complex [Ru(bbta)Cl(PPh3)2] (7). DFT calculations and the IR spectra of the carbonyl complex 6 reveal ligand 3 to be a less electron‐donating ligand compared to the bis(1H‐pyrazol‐1‐yl)acetic acid Hbpza. In case of the 1H‐1,2,4‐triazole‐based ligand 5 formation of coordination polymers were observed as proven by the synthesis of [Zn(btp)2]∞ (8) and [Mn(btp)2]∞ (9). Polymer 8 crystallises in linear chains of zinc atoms bridged by two molecules of ligand 5 each. These polymer chains show an interesting π‐stacking interaction between uncoordinated triazole residues of the ligands. Deposition of the coordination polymer on highly ordered pyrolytic graphite (HOPG) was successful and was analysed by scanning tunnelling microscopy (STM). Reaction of Na[btp] (5) with MnSO4·H2O resulted in a metal organic framework (MOF) [Mn(btp)2]∞ (9).