Bimolecular reactions of the chromium-benzyne ion Cr+C6H4 in the gas phase. An FT-ICR study

Abstract

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

The First Anionic Thia‐Fries Rearrangements at Ferrocene: Ready Access to Trifluoromethylsulfonyl‐Substituted Hydroxyferrocenes and an Extremely High Interannular Stereoinduction between Cyclopentadienyl Ligands

“…Subsequent treatment with LDA in THF at À78 8C results in another anionic thia-Fries rearrangement with formation of 2,5-bis(trifluoromethylsulfonyl)ferrocenol (14) in virtually quantitative yield. The respective methyl ether 15 can either be obtained by in situ quench with dimethyl sulfate or by methylation of 14 (Scheme 5).…”

“…After phase separation the organic layer was collected with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO 4 . After solvent removal 2,5-bis(trifluoromethylsulfonyl)ferrocenol (14) was isolated as an orange solid; yield: 2.00 g (17) 1-Methoxy-2,5-bis(trifluoromethylsulfonyl)ferrocene (15) At À78 8C LDA in THF [prepared from 1.6 M n-BuLi (2.7 mL, 4.4 mmol) in hexane and diisopropylamine (1.9 mL, 13.2 mmol) in THF (20 mL)] was added dropwise over 40 min to 2-(trifluoromethylsulfonyl)ferrocenyl triflate (13, 1.8 g, 4.4 mmol) in THF (20 mL). The color changed from light yellow to deep red.…”

“…After phase separation the organic layer was collected with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO 4 . After solvent removal the remaining solid [2,5-bis(trifluoromethylsulfonyl)ferrocenol (14)] was dissolved in THF (50 mL). At 25 8C NaH (0.2 g, 6.0 mmol, 80% in mineral oil) was added.…”

“…[13] In contrast, there is strong mass spectrometric evidence for the (benzyne)Cr + cation with the chromium atom attached at the cyclic p system. [14] As a matter of fact, the respective MS peak at m/z = 128 is the base peak in mass spectra of tricarbonylchromium complexes of benzocyclobutenedione, [14,15] indantrione, [16] indan-1,3-dione, [16] and acetals thereof as a result of fragmentation reactions. These findings caused our interest in the synthesis or trapping of p complexes of arynes and related systems.…”

Synthesis of Enantiopure Tricarbonyl(indan‐1,2‐dione)chromium

“…[14][15][16][17][18][19][20][21] We have contributed to this development in our investigations in the field of (arene)tricarbonylchromium complexes with functionalized anellated rings. [22][23][24] Key compounds in our research are complexes 1-4 of benzocyclobutenone, [22,[25][26][27][28][29][30][31] benzocyclobutenedione, [27,29,30,[32][33][34][35][36][37] 1,3-indandione, [38] and 1,2,3-indantrione. [38] In particular, chemistry relating to 1 and 2 has unveiled important oxy anion-accelerated reactions, such as anionic ring-opening reactions or dianionic oxyCope rearrangements, which take place under particularly mild reaction conditions.…”