Schröder D, Roithová J, Gruene P, Schwarz H, Mayr H, Koszinowski K. Unexpected Gas-Phase Reactivity of the CH3OH Adduct of Michler's Hydrol Blue: Proton-Shuttle Catalysis and Stepwise Radical Expulsions.
J Phys Chem A 2007;
111:8925-33. [PMID:
17718550 DOI:
10.1021/jp073950g]
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Abstract
Electrospray ionization of a methanolic solution of Michler's hydrol blue, bis(4-(N,N-dimethylamino)phenyl)methyl tetrafluoroborate, 1+BF(4)-, produces the formal methanol adduct [1+.CH(3)OH], which shows an unusual gas-phase chemistry. Tandem mass-spectrometry experiments and complementary theoretical studies indicate that this adduct corresponds to the methyl ether of Michler's hydrol protonated at one of the dimethylamino groups, cation 3+. Collision-induced dissociation of mass-selected 3+ leads to two sequential expulsions of open-shell species, resulting in a formal loss of [C(2)H(6)O], whereas no expulsion of methanol is observed. In contrast, interaction of gaseous 3+ with a single molecule of a suitable base triggers an exoergic loss of methanol via proton-shuttle catalysis within the collision complex. The occurrence of this exothermic proton transfer also prevents the application of the otherwise successful kinetic method for the determination of the gas-phase proton affinity of the methyl ether of Michler's hydrol.
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