(PENTAMETHYLCYCLOPENTADIENYL)SELENIUM DERIVATIVES .5. BIS(PENTAMETHYLCYCLOPENTADIENYL)SELENIUM AND ITS REACTIONS WITH TRANSITION-METAL CARBONYLS

The first cyclopentadienylselenium derivative, Se(C5Me5)(2) (1), has b een prepared by the reaction of LiC5Me5 with selenium bis(diethyldithi ocarbamate). Steric crowding about the selenium atom in 1 results in l ong Se-C bonds and an expanded C-Se-C angle, giving rise to unpreceden ted reactivity. Treatment of 1 with sources of M(CO)(5) fragments yiel ds the terminal diselenide complexes [M(CO)(5){Se-2(C5Me5)(2)}] (M = C r, W) via reduction within the transition-metal coordination sphere. R eaction of 1 with [Fe-2(CO)(9)] leads to loss of both C5Me5 groups and formation of [Fe3Se2(CO)(9)].