Large Effect of a Small Substitution: Competition of Dehydration with Charge Retention and Coulomb Explosion in Gaseous [(bipyR)Au(μ-O)2Au(bipyR)]2+ Di

详细信息    查看全文

• 作者：Eric C. Tyo ; A. W. Castleman ; Jr. ; Detlef Schrder ; Petr Milko ; Jana Roithova ; Jean Michel Ortega ; Maria Agostina Cinellu ; Fabio Cocco ; Giovanni Minghetti
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：September 16, 2009
• 年：2009
• 卷：131
• 期：36
• 页码：13009-13019
• 全文大小：374K
• 年卷期：v.131,no.36(September 16, 2009)
• ISSN：1520-5126

文摘

Dinuclear gold(III) clusters with a rhombic Au₂O₂ core and 2,2′-bipyridyl ligands substituted in the 6-position (bipy^R) are examined by tandem mass spectrometry. Electrospray ionization of the hexafluorophosphate salts affords the complexes [(bipy^R)Au(μ-O)₂Au(bipy^R)]²⁺ as free dications in the gas phase. The fragmentation behavior of the mass-selected dications is probed by means of collision-induced dissociation experiments which reveal an exceptionally pronounced effect of substitution. Thus, for the parent compound with R = H, i.e., [(bipy)Au(μ-O)₂Au(bipy)]²⁺, fragmentation at the dicationic stage prevails to result in a loss of neutral H₂O concomitant with an assumed rollover cyclometalation of the bipyridine ligands. In marked contrast, all complexes with alkyl substituents in the 6-position of the ligands (bipy^R with R = CH₃, CH(CH₃)₂, CH₂C(CH₃)₃, and 2,6-C₆H₃(CH₃)₂) as well as the corresponding complex with 6,6′-dimethyl-2,2′-dipyridyl as a ligand exclusively undergo Coulomb explosion to produce two monocationic fragments. It is proposed that the additional steric strain introduced to the central Au₂O₂ core by the substituents on the bipyridine ligand, in conjunction with the presence of oxidizable C−H bonds in the substituents, crucially affects the subtle balance between dication dissociation under maintenance of the 2-fold charge and Coulomb explosion into two singly charged fragments.