Photochemical ring-contraction of a tetrasilaferracyclohexane of the (η5-C5H4)Fe(CO)2 system to trisilaferracyclopentanes

Treatment of (eta(5)-C5H5)Fe(CO)(2)(SiMe2)(n)Cl (n = 3, 4) with lithium diisopropylamide leads directly to new trisila- (1) and tetrasilaferracycles (2) [(eta 5-C5H4)Fe(CO)(2)(SiMe2)(n)]. The trisilaferracycle (1) exhibits a degree of ring strain as noted by Si-29 NMR spectroscopy and single-crystal X-ray analysis but is stable with respect to limited attempts at ring-opening polymerization and photochemical transformation. In contrast, 2, with no ring strain, readily transforms via photochemical irradiation by way of iron silyl(silylenes) to a trimethylsilyl-substituted trisilaferracycle 4, which in turn transforms to 1 upon prolonged irradiation.