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

Abstract

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 for further understanding the physicochemical properties of Ru(II)–arene complexes in solution. Methods All mass spectra were collected with an AB SCIEX TripleTOF 5600+ mass spectrometer in positive mode. Theoretical calculations were carried out using 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 ruthenated [15]paracyclophanes (Ru‐[15]PCPs) and Ru(II)–arene dimers were dissolved in alkyl alcohol solvents, the adducts of alkoxides with Ru(II)–arene cations were observed under positive ion mode ESI‐MS, which resulted from the coordination of alkyl alcohol molecules with the Ru(II)–arene cations followed by the deprotonation of O‐H bonds of 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 signal intensity of the adducts of methoxides with Ru(II)–arene cations was the strongest among the 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 alkyl alcohol solvents. Taking into consideration the solubility and signal response, methanol is the most suitable solvent for the ESI‐MS experiments with Ru(II)–arene complexes among the solvents studied, where almost only the diagnostic adducts of methoxides with Ru(II)–arene cations are present.