Synthesis, characterization and computational modeling of cyclen substituted with dendrimeric branches. Dendrimeric and macrocyclic moieties working together in a collective fashion

Abstract

A molecular system, formed by the aza-macrocycle known as cyclen and functionalized dendrons, was synthesized in a convergent fashion. An aliphatic spacer between the two molecular units was incorporated to avoid the sterical hindrances. The N-acylation reactions to carry out the cyclen substitution, particularly those in solid state, resulted in very good yields since no further purifications were necessary. The obtained molecular system was characterized by common spectroscopic techniques. According to X-ray analysis (powder analysis), there is a random arrangement of the molecules, with an average interplanar distance (the most recurrent) of 4.8 Å between first neighbors. A theoretical study at DFT level of theory was carried out, simulating the inclusion process of Ni 2+ into two different model molecules ( A and C), with and without dendrons present. According to the calculated interaction energies in the inclusion process, there is a significant contribution in terms of energy (−60.89 Kcal/mol) due to the presence of functionalized dendrons, which enfold the metal ion, forming a molecular cage and increasing in this way the degree of pre-organization due to cooperative effects created by the dendrimeric environment. These molecular arrangements would be relevant in areas like catalysis, having influence on the selectivity of catalytic processes, by controlling the accessibility of the active site (the metal atom) via sterical hindrances. Further experimental work of the incorporation of metal ions of the first transition series will be done in a rational way, taking into account the theoretical results obtained so far.