Nitrosonium complexes of resorc[4]arenes: spectral, kinetic, and theoretical studies.
Resorc[4]arene octamethyl ethers 1-3, when treated with NOBF4 salt in chloroform, form very stable 1:1 nitrosonium (NO+) complexes, which are deeply colored. The complexation process is reversible, and the complexes dissociate and bleach upon addition of methanol or water, to give the starting macrocycles. Resorc[4]arenes 1 and 2 are in the same cone conformation, but with different side-chains, whereas 3 possesses a different conformation (chair), while bearing the same side-chain as 2. Kinetic and spectral UV-visible analysis revealed that NO+ interacts with resorc[4]arenes 1 and 2 both outside and inside their basket, leading to complexes with two absorption patterns growing at different rates, one featuring high-energy bands (HEB) within the near-UV zone, and the other one low-energy bands (LEB), attributed to charge-transfer interactions, within the visible range. The presence of ester carbonyl groups in 2 strongly drives the NO+ cation outside the resorcarene. Resorc[4]arene 3 showed a spectral pattern pointing out a clear involvement of the ester moieties in the NO+ entrapping, beside the formation of significant charge-transfer interactions. 1H NMR spectroscopy and molecular modeling clearly supported these findings.
Botta
Bruno
B
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università La Sapienza, P.le A. Moro 5, 00185 Roma, Italy. bruno.botta@uniroma1.it
D'Acquarica
Ilaria
I
Delle Monache
Giuliano
G
Nevola
Laura
L
Tullo
Danila
D
Ugozzoli
Franco
F
Pierini
Marco
M