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Probing the Effect of Organic and Organometallic Functionalization on [1,5]-Silicon Shifts in Indenylsilanes

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journal contribution
posted on 26.01.2000, 00:00 by Mark Stradiotto, Paul Hazendonk, Alex D. Bain, Michael A. Brook, Michael J. McGlinchey
Indenylsilanes bearing organic and organometallic substituents have been prepared in order to probe the effect of substitution on the rate of [1,5]-silicon shifts in this class of compounds. In an attempt to prepare 1,1,3-tris(trimethylsilyl)indene (7), the hitherto unknown silicon-functionalized bis(trimethylsilyl)dibenzo[a,d]fulvalene (9) was unexpectedly generated; this species was characterized by use of both NMR spectroscopy and X-ray crystallography and was rationally prepared in 68% yield from 3,3‘-bis(1-(trimethylsilyl))indene (16). The molecular dynamics of 1,3-dimethyl-1-(trimethylsilyl)indene (18) and the crystallographically characterized chromium complex (η6-1,3-dimethyl-1-exo-(trimethylsilyl)indene)tricarbonylchromium (22) were examined by use of 1D-selective inversion and 2D-EXSY NMR techniques; surprisingly, the presence of chromium and methyl substituents has a negligible effect on the rate of [1,5]-silicon shifts (ΔG = 23−24 kcal mol-1) versus the parent compound 1-(trimethylsilyl)indene (3) (ΔG ≈ 24 kcal mol-1). In the case of 18, the intermediate isoindene 18-iso was intercepted with tetracyanoethylene as the crystallographically characterized [4 + 2] cycloadduct 5,6-benzo-2,2,3,3-tetracyano-1,4-dimethyl-7-(trimethylsilyl)bicyclo(2.2.1)hept-5-ene (19).