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School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Victoria 3010, Australia
E-mail: gkhai@unimelb.edu.au
; Fax: +61 3 9347-5180
; Tel: +61 3 8344-2452
b
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Australia
Dalton Trans., 2013, Advance Article
DOI:
10.1039/C2DT32143B
Received
17 Sep 2012,
Accepted
12 Nov 2012
First published online
27 Nov 2012
Alkynylsilver cations, RCCAg2+ (where R = Me and Ph) have been prepared in the gas phase using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. Two methods were used: (i) electrospray ionisation (ESI) of a mixture of AgNO3 (in MeOH/H2O/acetic acid) and the alkyne carboxylic acid to yield the appropriate silver acetylide cations RCCAg2+, via a facile decarboxylation of the RCCCO2Ag2+ precursor; (ii) ESI of silver acetylides, RCCAg, which yields a cluster of the type, [(RCCAg)12Ag2Cl]+. Regardless of the method of preparation, these alkynylsilver cations, RCCAg2+, undergo ion-molecule reactions with allyliodide to yield the ionic products Ag2I+ and [(RCCCH2CHCH2)Ag]+. The CID spectrum of [(PhCCCH2CHCH2)Ag]+ was compared to that of an authentic sample of the silver adduct of 5-phenyl-1-penten-4-yne. Both ions fragment to yield Ag+ and the radical cation, PhCCCH2CHCH2+˙, confirming that C–C bond coupling has taken place in the gas phase. DFT calculations were carried out on these C–C bond coupling reactions for the system R = Me. The reaction is highly exothermic and involves the initial coordination of the allyliodide to both silver atoms, with the iodine coordinating to one atom and the alkene moiety coordinating to the other. The overall mechanism of C–C bond coupling involves oxidative addition of the allyliodide followed by reductive elimination of RCCCH2CHCH2, to ultimately yield two sets of reaction products: (i) Ag2I+ and RCCCH2CHCH2; and (ii) [(RCCCH2CHCH2)Ag]+ and AgI.