Activation of aromatic rings by early transition metal ions in the gas phase. Implications for the metal-catalyzed [2 + 2 + 2] cycloaddition of alkynes and nitriles

✍ Scribed by R. Marshall Pope; Steven W. Buckner

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 538 KB
• Volume: 28
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210281238

✦ Synopsis

The reactions of a series of monocyclic and bicyclic arenes with early transition metal ions (Sc+, Y+, N b * and Ta') and their oxides and dioxides were studied in a Fourier transform ion cyclotron resonance mass spectrometer. Ring cleavage of the nitrogen-containing heterocycles results in loss of HCN as the dominant pathway. Thermoche-mica1 considerations, secondary reactions and correlations with solution cyclotrimerization reactions indicate that the MC,H,+ product is a metallacyclopentadiene. Based on correspondence between the reactivities of a series of early metals with their valence electron counts, the reactivities of quinoline and isoquinoline and the decomposition behavior of the products, a metallacycloheptatriene intermediate is proposed for the heteroaromatic ring cleavage reaction. These results are compared to metal complexes in solution which catalyze the 12 + 2 + 21 cyclotrimerization of alkynes and nitriles.