Distinctive Unimolecular Gas-Phase Reactivity of [M(en)2]2+ (M = Ni, Cu) Dications and Their Inclusion Complexes with the Macrocyclic Cavitand Cucurbit[8]uril

Electrospray ionization mass spectrometry makes it possible to generate gas-phase bis-ethylenediamine nickel and copper dications, [M(en)2]2+ (M = Ni, 1; M = Cu, 2), as well as their {[M(en)2]@cuc[8]}2+ inclusion complexes with the macrocyclic cavitand cucurbit[8]uril (cuc[8]). The unimolecular gas-phase reactivity of these species has been investigated by electrospray ionization tandem mass spectrometry with a quadrupole-time-of-flight configuration. Distinctive fragmentation pathways have been observed for the free and encapsulated [M(en)2]2+ (M = Ni, Cu) dications under collision-induced dissociation (CID) conditions. The dications [M(en)2]2+ (M = Ni, Cu) dissociate according to several competitive pathways that involve intra-complex hydrogen or electron-transfer processes. Most of these channels are suppressed after encapsulation inside the cucurbit[8]uril macrocycle and, as a consequence, a simplification of the {[M(en)2]@cuc[8]}2+ fragmentation pattern is observed. The results obtained demonstrate that the encapsulation of a coordination complex inside a host molecule can be used to alter the nature of the product ions generated under CID conditions.