C-H and C-C bond activation reactions in silver alkynyl cluster cations, RCCAg2+

A range of silver alkynyl cations RC CAg2+ (R = H, Me, Et, Pr, Bu, tBu and Ph) can be "synthesized" in the gas phase via two approaches using electrospray ionization (ESI) multistage mass spectrometry experiments. The first involves injecting a solution of AgNO3 and the appropriate acid RC CCO2H in a MeOH/H2O solvent mixture into the ESI source, which yields the cluster cations (RC CAg)(n)Ag+ (n = 1-12) via decarboxylation. The second involves direct ESI of solutions of pre-synthesized silver acetylides, which yields a series of silver acetylide cluster cations of the type (RC CAg)(n)Ag+ (n = 4-18), which upon CID yield RC CAg2+. The low energy CID reactions of the silver alkynyl cations RC CAg2+ have been studied in a linear ion trap mass spectrometer. The rich fragmentation reactions observed included various combinations of C-C and C-H bond activation to yield the ionic products: (1) CH3C CAg2+ (R = Pr, Bu); (2) Ag2H+ (R = Et, Pr, Bu, tBu); and (3) HC CAg2+ (R = tBu). Other fragmentation channels observed include; Ag-C bond cleavage and loss of Ag+. CID of the deuterium labelled cation, CD3CH2CH2C CAg2+ (m/z 284), show that: HID scrambling is not involved in either the loss of CD2=CH2 or the formation of Ag2H+ (m/z 215). Formation of the latter ion involves the regioselective activation of the C-H bond beta to the triple bond, as revealed by the formation of Ag2D+ (m/z 216) in the CID spectrum of the deuterium labelled cation, CD3CD2CH2C CAg2+ (m/z 286). (C) 2013 Elsevier B.V. All rights reserved.