C₅Me₅/ER-Ligated Samarium(II) Complexes with the Neutral “C₅Me₅M” Ligand (ER = OAr, SAr, NRR‘, or PHAr; M = K or Na):  A Unique Catalytic System for Polymerization and Block-Copolymerization of Styrene and Ethylene

Abstract

Reactions of (C 5 Me 5

η6:η6 Coordination of Tetraphenylborate to Ytterbium(II): A New Class of Lanthanoid ansa‐Metallocenes

“…[20] With allowance for differences in coordination number, the upper limit for Yb-C bonding in 2a and 3 [3.050(2) Å] is comparable with or well below the upper value for the preceding two complexes, [19,20] whilst the current Yb-C distance range (Table 1) is comparable or smaller. In the metallocene complex [Yb{N(SiMe 3 ) 2 }(C 5 Me 5 ) 2 Na(THF) 3 ], [21] which has an analogous ytterbium coordination environment to that of 3 ]. [21] This difference is also likely to be influenced by the decreased steric bulk of 3 (two Ph groups compared with two C 5 Me 5 groups) and the boron linkage in the chelating BPh 4 -ligand, and this results in a more open residual coordination sphere.…”

“…In the metallocene complex [Yb{N(SiMe 3 ) 2 }(C 5 Me 5 ) 2 Na(THF) 3 ], [21] which has an analogous ytterbium coordination environment to that of 3 ]. [21] This difference is also likely to be influenced by the decreased steric bulk of 3 (two Ph groups compared with two C 5 Me 5 groups) and the boron linkage in the chelating BPh 4 -ligand, and this results in a more open residual coordination sphere. The centroid-Ybcentroid angle (Ph*-Yb-Ph* 114.0°) is significantly smaller for 3 than for [Yb{N(SiMe 3 ) 2 }(C 5 Me 5 ) 2 Na(THF) 3 ] (Cp*-Yb-Cp* 134°).…”

“…The centroid-Ybcentroid angle (Ph*-Yb-Ph* 114.0°) is significantly smaller for 3 than for [Yb{N(SiMe 3 ) 2 }(C 5 Me 5 ) 2 Na(THF) 3 ] (Cp*-Yb-Cp* 134°). [21] The Ph*-Yb-Ph* angles are also considerably more acute than for BPh 4 -in [Nb(RCϵCR)(η 6 -Ph) 2 BPh 2 ] (131.6°). [4] Complex 3 has a Yb-C(Me) distance [2.845(8) Å] that is much shorter than a similar interaction in 1b [3.123(4) Å [16] ) but comparable to those of [Yb{N(SiMe 3 ) 2 } 2 ] 2 [2.785(4)-2.823(4) Å], which has several agostic Yb-Me 3 Si interactions to support the YbN 3 coordination.…”

Groups 3 and 4 single-site catalysts for styrene–ethylene and styrene–α-olefin copolymerization

“…The incorporated styrene amount in the copolymer also increased almost linearly with rising the styrene feed. 13 C NMR and viscoelasticity analyses confirmed the blocky nature of the copolymers: these materials proved to be mechanically much stronger and more flexible than a mixture of homopolymers [92].…”

“…Reactions initiated by styrene polymerization afforded only PS, indicating that the propagation site in the system does not allow ethylene insertion, although it can generate a species (possibly a Sm III -hydride) active for ethylene homopolymerization. The proposed mechanism for ER = aryloxide [92], thiolate [92], arylamide [92] and alkyl [93] complexes is depicted in Scheme 3.…”