Regioselective Coordination toward Silver(I) Ions by Bis- and Tris(Tetra-Armed Cyclen)s via Differential Electron Density of Aromatic Side Arms

Four types of bis- and tris(tetra-armed cyclen)s were prepared. 2 MF is a bis(tetra-armed cyclen) with electron-rich side arms (three 4-methoxybenzyl groups) and electron-deficient side arms (three 3,5-difluorobenzyl groups), connected by a 4,4′-dimethyl-1,1′-biphenyl moiety. 3 MFM is a tris(tetra-armed cyclen) with 4-methoxybenzyl and 3,5-difluorobenzyl groups introduced on both ends and the central cyclen, respectively. 4 MFM is a V-shaped analogue of 3 MFM . 3 FMF is a tris(tetra-armed cyclen) where the aromatic side arms at both ends and the central cyclen of 3 MFM are exchanged. The regioselective coordination of silver(I) ions by these ligands is reported. Initially, we added Ag + ions to a compound ( 2 MF ) that consists of tetra-armed cyclen with 4-methoxybenzyl groups as an electron-donating substituent on the aromatic rings and 3,5-difluorobenzyl groups as an electron-withdrawing substituent. 1 H NMR and 19 F{ 1 H} NMR spectroscopy exhibited that the cyclen with the 4-methoxybenzyl groups formed a complex with Ag + ions first, followed by the cyclen with the 3,5-difluorobenzyl groups. Next, we employed a compound ( 3 MFM ) with three cyclen units, where the cyclen at each end was functionalized with three 4-methoxybenzyl groups, and the central cyclen was functionalized with two 3,5-difluorobenzyl groups. Upon adding Ag + ions, we observed that the cyclen units at both ends formed complexes with Ag + ions initially, followed by the central cyclen forming a complex with Ag + ions. When we used 4 MFM, which is a V-shaped compound, the Ag + -induced- 1 H NMR chemical shift changes are almost the same results as the 3 MFM . Furthermore, we synthesized a compound ( 3 FMF ) by interchanging the substituents on the cyclen units at the ends and the center. Interestingly, the order of the complex formation was reversed in this compound. These results demonstrated that tuning the electron density on the aromatic side arms through substituents makes it possible to achieve regioselective coordination with Ag + ions in bis- or tris(tetra-armed cyclen)s.