FORMATION OF STABLE ORGANOMETALLIC PLANAR-TETRACOORDINATE CARBON-COMPOUNDS CONTAINING A CATIONIC (MU-R(1)CCR(2))[MU-CHLORO(ZRCP(2))(2)] FRAMEWORK

The methylzirconocene cation [Cp(2)ZrCH(3)(THF)(+)BPh(4)(-)] reacts wi th Cp(2)Zr(Cl)(C=C-R) reagents (5a-c, R=-CH(2)Ph,-CH2CH2CH3,-CH3) to y ield the dinuclear metallocene cations [(Cp(2)Zr)(2)(mu-Cl)(mu-eta(1) : eta(2)-RCCCH(3)](+) (6a-c) (with BPh(4)(-) anion) that contain a pla nar-tetracoordinate carbon atom. Complex 6b was characterized by X-ray diffraction. The activation energy of the degenerate rearrangement of 6c was determined by temperature dependent dynamic H-1 NMR spectrosco py (Delta G double dagger(240 K) = 11.3 +/- 0.5 kcal mol(-1)).