Probing the effect of organic and organometallic functionalization on [1,5]-silicon shifts in indenylsilanes

Indenylsilanes bearing organic and organometallic substituents have been pr epared in order to probe the effect of substitution on the rate of [1,5]-si licon shifts in this class of compounds. In an attempt to prepare 1,1,3-tri s (trimethylsilyl)indene (7), the hitherto unknown silicon-functionalized b is(trimethylsilyl)dibenzo[a,d]fulvalene (9) was unexpectedly generated; thi s species was characterized by use of both NMR spectroscopy and X-ray cryst allography and was rationally prepared in 68% yield from 3,3'-bis(1-(trimet hylsilyl))-indene (16). The molecular dynamics of 1,3-dimethyl-1-(trimethyl silyl)indene (18) and the crystallographically characterized chromium compl ex (eta(6)-1,3-dimethyl-1-exo-(trimethylsilyl)-indene)tricarbonylchromium ( 22) were examined by use of 1D-selective inversion and 2D-EXSY NMR techniqu es; surprisingly, the presence of chromium and methyl substituents has a ne gligible effect on the rate of [1,5]-silicon shifts (Delta G(double dagger) = 23-24 kcal mol(-1)) versus the parent compound 1-(trimethylsilyl)indene (3) (Delta G(double dagger) approximate to 24 kcal mol(-1). In the case of 18, the intermediate isoindene 18-iso was intercepted with tetracyanoethyle ne 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).