Tethered olefin studies of alkene versus tetraphenylborate coordination and lanthanide olefin interactions in metallocenes

The tethered olefin cyclopentadienyl ligand, [(C5Me4)SiMe2(CH2CH=CH2)](-), forms unsolvated metallocenes, [(C5Me4)SiMe2(CH2CH=CH2)](2)Ln (Ln = Sm, 1; Eu, 2; Yb, 3), from [(C5Me4)SiMe2(CH2CH = CH2)]K and Lnl(2)(THF)(2) in good yield. Each complex in the solid state has both tethered olefins oriented toward the Ln metal center with the Ln-C(terminal alkene carbon) distances 0.2-0.3 Angstrom shorter than the Ln-C(internal alkene carbon) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5) Angstrom, respectively, are normal. Like its permethyl analogue, (C5Me5)(2)Sm(THF)(2), complex 1 reductively couples CO2 to form the oxalate-bridged dimer {[(C5Me4)SiMe2(CH2CH=CH2)](2)Sm)(2)(mu-eta(2):eta(2)-O2CCO2), 4, in which the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh4 to form an unsolvated cation that has the option of coordinating [BPh4](-) or a pendant olefin, a competition common in olefin polymerization catalysis. The structure of {[(C5Me4)SiMe2(CH2CH=CH2)](2)Sm}[BPh4], 5, shows that both pendant olefins are located near samarium rather than the [BPh4](-) counterion.