Combining a Phenanthroline Moiety with Two Peralkylated Guanidine Residues: Janus Head Pro‐Ligands

Abstract

A novel family of Janus head pro‐ligands is described that combine a phenanthroline moiety with two peralkylated guanidine residues. The bis‐bidentate molecules provide coordination sites with metal‐differentiating properties and thus are especially well suited to form heterobinuclear complexes. Synthesized members of this family differ in their substitution patterns and comprise variants with tetramethyl‐, tetraethyl‐, dipentylene‐, dimethylethylene‐, and dimethylpropylene‐guanidino functionalities. They were characterized by low‐temperature X‐ray crystallography and studied by means of temperature‐dependent 1H NMR spectroscopy, which provided information on the dynamics of their guanidine moieties. Furthermore, the redox behavior was investigated by using cyclic voltammetric techniques.

Combining a Phenanthroline Moiety with Peralkylated Guanidine Residues: Homometallic CuII, NiII and ZnII Halide Complexes with Site‐Differentiating Janus Head Ligands

“…To evaluate the charge delocalization within the guanidine function, a structural parameter termed ρ has been introduced which is defined as the ratio of twice the length of the C Gua =N Imine bond a and the sum of the lengths of the two C Gua –N Amine bonds b and c : ρ = 2 a /( b + c ). [14f] In case of 4 and 6 , the mean ρ values are 0.94 and 0.96, respectively (Table ), which is an evidence for localized double bonds with limited degrees of delocalization as it was shown for the free ligand B ( ρ = 0.93) . Consequently, the delocalization of the guanidine double bond is virtually not affected by metalation of the phenanthroline binding sites.…”

“…Consequently, the delocalization of the guanidine double bond is virtually not affected by metalation of the phenanthroline binding sites. On the contrary, entire charge delocalization within the metalated guanidine units of 7 – 12 is indicated by mean ρ values ranging between 1.00 and 1.03 (Table ) . For 13 and 14 , the calculated ρ data suggest an almost complete delocalization of the double bond over the guanidine functionalities (0.99 and 0.98; Table ).…”

“…Recently, the angle between the planes N Amine –N Imine –N Amine and C Amine –C Gua –C Amine of the guanidine moiety has been described as the guanidine twist. [16b], [25a] The individual average values of the non‐coordinated guanidine units within 4 and 6 are slightly smaller than in the free ligand B (13.5°) with 12.0 and 11.5° (Table ). For the metalated DMEG functionalities within 9 , a smaller dihedral angle (8.5°) in comparison to 4 and 6 of the free ligand B is observed, while in the case of 14 it is in the order of the values established in 4 and 6 (12.2°).…”

“…Quite recently, the first non‐symmetrical bis(guanidines) with different peralkylated units have been synthesized . The guanidine functionality is widespread in Nature itself and is a perfect mimic for histidine residues in matters of basicity . This basicity provides a better solubility by protonation and enables consequently the application of guanidines as proton reservoirs.…”

“…Previously, we combined an 1,10‐phenanthroline moiety with two peralkylated guanidine residues in positions 5 and 6 to gain access to novel bis‐bifunctional Janus head pro‐ligands (Scheme ) . In this work, in order to evaluate their coordination properties, a variety of copper(II), nickel(II) and zinc(II) halide complexes containing the hybrid ligands phenTMG (tetramethyl‐guanidino, A ), phenDMEG (dimethylethylene‐guanidino, B ), phenTEG (tetraethyl‐guanidino, C ) and phenDPG (dipentylene‐guanidino, D ) has been prepared.…”