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Studies in negative ion mass spectrometry: XIV —Electron attachment reactions of a series of η 6 ‐arenetricarbonylchromium(O) complexes
Author(s) -
Blake M. R.,
Garnett J. L.,
Gregor I. K.,
Wild S. B.
Publication year - 1980
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210150711
Subject(s) - chemistry , mass spectrum , ion , substituent , ligand (biochemistry) , polyatomic ion , fragmentation (computing) , decarbonylation , electron ionization , medicinal chemistry , molecule , stereochemistry , crystallography , organic chemistry , biochemistry , receptor , computer science , catalysis , ionization , operating system
Electron attachment reactions of a series of (η 6 ‐arene)tricarbonylchromium(O) complexes have been examined in the gas phase. The electron capture process has been shown to be influenced by the structure of the η 6 ‐arene ligand and its substituents. Whereas (η 6 ‐benzene)‐ and (η 6 ‐mesitylene)tricarbonylchromium(O) undergo dissocative electron capture, or reductive decarbonylation, yielding [MCO] − ˙ ions of highest abundance in their negative ion mass spectra, [η 6 ‐(2,2‐dimethylindan‐1,3‐dione)]tricarbonylchromium(O) forms a molecular negative ion which undergoes sequential CO eliminations and finally a demetallation to give the arene radical ion. A localization of charge on the coordinated arene ligand is proposed for the formation of [M] − ˙ in this case. (η 6 ‐Methylbenzoate)tricarbonylchromium(O) also forms a molecular negative ion by secondary electron attachment which decomposes by simultaneous and consecutive eliminations of up to four CO molecules. The elucidation of a mechanism and sequence for these CO eliminations has been achieved by synthesizing and examining the negative ion mass spectrum of [η 6 ‐(C 6 H 5 · 13 CO 2 Me)]Cr(CO) 3 . The first CO loss in the principal fragmentation pathway occurs solely from the –Cr(CO) 3 group of [M] − ˙. The effect of para substituent groups on the stabilities of molecular negative ions and their fragmentations has been ascertained using a series of para ‐substituted (η 6 ‐methylbenzoate)tricarbonylchromium(O) compounds containing the groups NH 2 , OH, OCH 3 , CL and COOMe. The stabilities of the [M] − ˙ ions have been rationalized in terms of the Hammett and Taft parameters σ P , σ I , σ R P , σ P O and σ R O . The overall electronic substituent effect transmitted to the carbonyl groups of the –Cr(CO) 3 unit involves both resonance and inductive components. In this series of compounds the stability of [M] − ˙ decreases as the electron withdrawing capacities of the para substituents increase.