The chromium-benzyne ion Cr+-C H4 was generated in the gas phase by electron-impacbinduced loss of 5 CO from (~6-1,2-dioxocyclobuta~nzene)tricarbonylchromium(O). The gas-phase reactions of the Cr+-C& ions with methanol, ammonia, several alkanes, alkadienes, and aromatic species were studied by Fourier transform ion cyclotron resonance spectrometry (FT-ICR) using an external ion source. The results show that the bimolecular reactivity of the Cr+-C6H4 cations is determined by the C6H4 ligand, exhibiting the high reactivity of benzyne. No reactions due to a primary reaction at Cr+ are discovered. In moet of the reactions, the main product observed for the bimolecular reaction is Cr+ released from the complex by the great exothermicity of the d o n at the C$i, ligand. However, in the a s e of lees exothermic reactions and if the excess energy is removed from the reaction complex by "evaporati@ a neutral leaving group, Cr+ complexes are observed whose ligands arise from addition reactions of the reactants to C$4. This is the case for cycloadditions of benzene-d8 and naphthalene-d8 to Cr+-C6H4, where the adducts shll containing Cr+ as well as ions formed by loas of acetylene-d2 from the adducts are observed. Thus, in the family of transition-metal-cation-benzyne complexes, the cation is extraordinary in exhibiting reactivity exclusively at the benzyne ligand. IntroductionThe study of the gas-phase reactions of bare transition-metal cations with organic substrates during the last few years has given a wealth.of information about organometallic chemistry.' A typical gas-phase reaction of a transition-metal ion with a hydrocarbon is the oxidative insertion into C-H and C-C bonds. Besides the investigation of the reactivity of bare metal ions, a study of the modification of the reactivity of the central metal ions of mrdinatively unsaturated metal complexes by the ligands is a major field of research in metal-organic chemistry.2 Usually the complexation of ligands alters the reactivity

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Carbonyl protonated aromatic ketones a

Reactions of the j3-Distonic Ion +CH,OCH,CH,' with Butyronitrile: Evidence for an Intermediate Three-body Ion-Neutral Complex during DeprotonationDistonic ions are reactive intermediates of organic gas-phase reactions exhibiting very interesting properties.' In a previous publication2 we discussed the unimolecular and bimolecular reactions of the B-distonic ion +CH20CH,CH2* (a). Using the deuterated ions +CH,0CD2CD; (b) and fCD20CH2CH,' (c), it was shown that a transfers a C2HZ' unit and a CHO' unit to acetonitrile and pyridine, respectively, without any H/D scrambling, corroborating in the case of the C2HZ' transfer earlier observations of Baumann et al. ' The structural integrity of +CH20CH2CH2' revealed by these reactions is attributed to the unique thermodynamic stability of B-distonic ions., However, a second abundant reaction of a is the transfer of a proton to acetonitrile and pyridine, respectively; and from b as well as from c H+-and D+-transfer is observed. Obviously, each of the hydrogen atoms of a is transferred with a certain probability. This may be due either to parallel proton transfers from each of the different positions of a or a H/D scrambling in a prior to the proton transfer, the latter explanation being in conflict with the strutural integrity of a in the other ion-molecule reactions. Both possibilities can be distinguished by a quantitative analysis of H-and D-transfer from the isotopomers b and c, because only in the case of a H/D scrambling (unit preference factor for all positions) are the experimental data described by a single isotope effect k J k D . However, we did not succeed in obtaining consistent quantitative data for the reaction of b and c with CH,CN because the intensity ratio [CH3CNH+]/[CH3CND+] increased continuously with the reaction time. It is very likely that the ion mixture in CH,CN contained some unknown impurities which we were not able to remove. Here we report the results for the reaction of a with n-butyronitrile showing that a indeed loses its structure prior to the transfer of a proton.The B-distonic ion a was generated by electron-impact induced fragmentation of 1,4-dioxane, in the external ion source of a Spectrospin CMS 47X Fourier transform-ion cyclotron resonance (FT-ICR) spectrometer. The resulting ions were transferred into the ICR cell filled with n-C,H,CN at a pressure of 4 x lo-' mbar. In order to study the reactions of b and c, 2,2,3,3-tetradeutero-1,2-dioxane was ionized in the external ion s o u~c e .~*~ The ions a, b and c, respectively, were isolated by removing all other ions using broad-band ejection and specific rf-pulses of low amplitude (' soft single shots') in the mass range of a, b and c. The isolated ions were thermalized by collisions with the reagent gas for 1.5 s, and any ions formed besides those to be studied were again ejected by single shots. Subsequently, mass spectra were obtained at intervals of 0.5 s during a total reaction time of ca. 5 s.