The base-free ytterbocenes (Me 5 C 5 ) 2 Yb, (Me 4 C 5 H) 2 Yb, and [1,3-(Me 3 C) 2 C 5 H 3 ] 2 Yb have been prepared from their diethyl ether adducts, synthesized by reaction of YbI 2 and the sodium salt of the substituted cyclopentadiene anion in diethyl ether. The structures of the basefree molecules have been determined by X-ray crystallography. The molecule (Me 5 C 5 ) 2 Yb has been found to crystallize in two different morphologies; the complex also forms inclusion complexes with toluene, ortho-carborane, meta-carborane, and 1,2-dimethyl-ortho-carborane. The ytterbocene molecule in all of the derivatives examined is bent in the solid state with centroid-metal-centroid angles ranging from 132°to 147°. A detailed examination of the structures and comparison with the reported structures of (Me 5 C 5 ) 2 Eu, (Me 5 C 5 ) 2 Sm, [1,3-(Me 3 Si) 2 C 5 H 3 ] 2 Yb, and [1,3-(Me 3 Si) 2 C 5 H 3 ] 2 Eu reveal that bending is the general structural preference. Close inter-or intramolecular contacts are observed in every case between the ytterbium atom and one or more carbon atoms other than those of the two cyclopentadienide rings of that ytterbocene fragment. The packing geometry is dictated by the substituents on the cyclopentadienide rings, the molecules arranging so as to minimize crowding in the solid state. The net result is a coordination polymer, dimer, or monomer, depending on the ring substituents.

The most Lewis acidic perfluoroarylborane prepared to date: the multicenter organo‐Lewis acid 1 is capable of forming both mono‐ and dianionic metallocenium counteranions, the olefin polymerization activities of which are up to 20 times higher than those of the analogous B(C6F5)3‐activated catalysts.

This contribution describes the implementation of the binuclear organotitanium "constrained geometry catalysts" (CGCs), (mu-CH(2)CH(2)-3,3'){(eta(5)-indenyl)[1-Me(2)Si((t)()BuN)](TiMe(2))}(2)[EBICGC(TiMe(2))(2); Ti(2)] and (mu-CH(2)-3,3'){(eta(5)-indenyl)[1-Me(2)Si((t)BuN)](TiMe(2))}(2)[MBICGC(TiMe(2))(2); C1-Ti(2)], in combination with the bifunctional bisborane activator 1,4-(C(6)F(5))(2)BC(6)F(4)B(C(6)F(5))(2) (BN(2)) in ethylene + olefin copolymerization processes. Specifically examined are the classically poorly responsive 1,1-disubstituted comonomers, methylenecyclopentane (C), methylenecyclohexane (D), 1,1,2-trisubstituted 2-methyl-2-butene (E), and isobutene (F). For the first three comonomers, this represents the first report of their incorporation into a polyethylene backbone via a coordination polymerization process. C and D are incorporated via a ring-unopened pathway, and E is incorporated via a novel pathway involving 2-methyl-1-butene enchainment in the copolymer backbone. In ethylene copolymerization, Ti(2) + BN(2) enchains approximately 2.5 times more C, approximately 2.5 times more D, and approximately 2.3 times more E than the mononuclear catalyst analogue [1-Me(2)Si(3-ethylindenyl)((t)BuN)]TiMe(2) (Ti(1)) + B(C(6)F(5))(3) (BN) under identical polymerization conditions. Polar solvents are found to weaken the catalyst-cocatalyst ion pairing, thus influencing the comonomer enchainment selectivity.