Investigating the exceptional adducts of alkoxides with Ru (II)-arene cations in alkyl alcohol solution using electrospray ionization mass spectrometry.

Cao, Xiaoji; Dong, Danqi; He, Dandan; Lin, Xupin

RATIONALE Exploring the formation mechanism of the exceptional adducts of alkoxides with Ru (II)-arene cations in alkyl alcohol solution using electrospray ionization mass spectrometry (ESI-MS) is crucial to further understand the physicochemical properties of Ru (II)-arene complexes in solution. METHODS All mass spectra were collected on an AB SCIEX TripleTOF 5600+ mass spectrometer in positive mode. Theoretical calculations were carried out by the density functional theory method at the B3LYP level with a hybrid basis set consisting of 6-31G(d,p) and LANL2DZ in the Gaussian 03 program. RESULTS When the ruthenated [15 ]Paracyclophanes (Ru-[15 ]PCPs) and Ru (II)-arene dimers were dissolved in the alkyl alcohol solvents, the adducts of alkoxides with Ru (II)-arene cations were observed under positive ion mode ESI-MS, which were resulted from the coordination of alkyl alcohol molecules with Ru (II)-arene cations followed by the deprotonation of O-H bond on the coordinated alcohols. Furthermore, the number of alkoxides binding to Ru-[15 ]PCPs was regulated by the number of ruthenium atoms. Attributed to good solubility and small steric hindrance, the intensity of the adducts of methoxides with Ru (II)-arene cations was the strongest among three alkyl alcohols used in this study. CONCLUSIONS The characteristic adducts of alkoxides with Ru (II)-arene cations were pervasively present in positive ion mode ESI-MS of nine Ru (II)-arene complexes dissolved in the alkyl alcohol solvents. Taking into consideration of the solubility and signal responding, the methanol is the most suitable solvent for the ESI-MS experiments of Ru (II)-arene complexes among the eight solvents studied, where almost only the diagnostic adducts of methoxides with Ru (II)-arene cation are present.