Can metal clusters assist silicon migrations? An NMR spectroscopic and X-ray crystallographic study

The indenyl-alkynylsilane, (η1-indenyl)SiMe2(CC–SiMe3) (3), and its Co2(CO)6 complex, 4, have been shown by 2D-EXSY NMR to undergo 1,5-silatropic shifts; for 3 the barrier is approximately 24 kcal mol−1. These processes involve the intermediacy of the corresponding isoindenes, which can be trapped as their Diels–Alder adducts with tetracyanoethylene; the X-ray structure of the cobalt adduct is described. These data suggest that any positive charge that develops at silicon during the rearrangement is only minimally delocalized onto the cobalt center.