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Comparison between a Diarylferrocenylmethylium Ion and Its Isolobal Cobalt Species:  Similarities and Differences

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journal contribution
posted on 24.12.1996, 00:00 by Rolf Gleiter, Holger Schimanke, Sandro J. Silverio, Michael Büchner, Gottfried Huttner
Reaction of {(1,2,8,9-η)-tricyclo[,7]tetradeca-1,8-diene}{η5-(methoxycarbonyl)cyclopentadienyl}cobalt (9) with either 2 mol of arylmagnesium bromide or aryllithium and subsequent hydrolysis yields the alcohols {(1,2,8,9-η)tricyclo[,7]tetradeca-1,8-diene}{η5-(diarylhydroxymethyl)cyclopentadienyl}cobalt (13ac). The treatment of the yellow colored alcohols 13ac with HBF4 in ether affords the tetrafluoroborates of the violet colored carbocations 14ac. Investigations of single crystals of 14b by means of the X-ray technique show a displacement of the C1−Cexo bond by α = 10.8° toward the metal and a pronounced bond alternation in the fulvene moiety. The bending of C1−Cexo is considerably larger than in the corresponding alcohol 13b (α = 2.5°). The interaction between the exo-carbon and the metal in 14b is further substantiated by comparison of the 13C-NMR chemical shift of 14b with 13b (Δδ = −65 ppm). The comparison of the data obtained for 14b with those of diphenylferrocenylcarbenium ion 1b suggests a stronger bonding between metal and fulvene moiety in 1b as compared to 14b. These results are substantiated by the results of ab initio calculations on 1b and 4a which show a smaller positive charge at the exo-carbon in 4a than in 1b and a stronger bond index between the exo-carbon and the metal in 1b as compared to 4a.