Photochemical ring-contraction of a tetrasilaferracyclohexane of the (η 5-C 5H 4)Fe(CO) 2 system to trisilaferracyclopentanes

Treatment of (η 5 -C5H5)Fe(CO)2(SiMe2) n Cl (n = 3, 4) with lithium diisopropylamide leads directly to new trisila- (1) and tetrasilaferracycles (2) [(η 5 -C5H4)Fe(CO) 2 (SiMe 2 ) n ]. The trisilaferracycle (1) exhibits a degree of ring strain as noted by 29 Si 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.