ansa-Metallocene derivatives XXXII. Zirconocene complexes with a spirosilane bridge: syntheses, crystal structures and properties as olefin polymerization catalysts

Abstract

Chiral ansa-zirconocene complexes with a trimethylene link between the Si bridge atom and an a-position of each C s ring ligand were prepared; two representatives, with i-propyl and t-butyl groups as f3-substituents, were structurally characterized. The properties of these complexes with respect to MAO-activated propene polymerization were studied in comparison with those of their Me 2 Si-bridged analogs. The t-butyl-substituted spirosilane complex gives a polymer with relatively high content of 3, I-insertions. These increased regioirregularities appear to be associated with decreased coordination gap aperture and increased lateral extension angles of the spirosilane-bridged zirconocene complexes; this notion is supported by a molecular-mechanics analysis of alternative olefin-insertion transition states.

Copolymerization of ethylene with propylene and higher α-olefins catalyzed by (imido)vanadium(iv) dichloride complexes

“…Indeed, it is known that a 2,1-insertion of propylene places the methyl in a peripheral position (rather than in the direction or plane of the metal), and the resultant intermediate transition state requires less space along the direction of metal aperture to undergo a 2,1insertion. 10,71 It is worth noting that Ʃx n,2i only indicates the minimum fraction of inverted propylene units since the calculated data neglects all the inverted units contained in the methylene sequences longer than six methylene units (n 6+ ), and 1,3-enchained propylene units arising from a 2,1→1,3…”

Cationic Group 4 Complexes (M = Ti, Zr, Hf): Modifications and Limitations in the Design of Tridentate Cp,O,P‐Ligand Frameworks Built Directly in the Coordination Sphere of the Metal

“…In regard to the achievements of the use of well‐defined cationic group 4 metal complexes and their role as important olefin polymerization catalysts, numerous substitution patterns for the ancillary ligand systems have been developed do direct their catalytic activity . For example, Brintzinger et al synthesized a silaspiro zirconocene complex, which posseses C 2 ‐symmetry, and showed that this complex is able to polymerize propylene to isotactic polypropylene after activation with methylaluminoxan (MAO) to the corresponding cationic complex . In contrast a quite similar C s ‐symmetric complex affords almost only atactic polypropylene …”

ansa-metallocene derivatives XXXIX biphenyl-bridged metallocene complexes of titanium, zirconium, and vanadium: Syntheses, crystal structures and enantioseparation

“…[3]). Increasing interest in chiral ansa-metallocenes, especially of Group 4 metals, as catalysts for stereoselective reactions [3,4] has been associated with substantial efforts to develop strategies which yield the pure racemic diastereomer [5][6][7][8][9][10][11][12][13][14][15][16].…”

“…A different approach is the incorporation of a second linker to prevent the bis(cyclopentadienyI) ligands from isomerization [12]. Chiral, doubly bridged [13] or spirobridged [14] substituted ligand systems have recently been designed which give solely the racemic metallocenes.…”