Ligands fluorenyl

Figure 1.8 Approximated transition states for primary propene insertion for model complexes with (a) isopropyl-bis(l-indenyl) ligand (isospecific) for the (R, R) coordination and (b) iso-propyl(cyclopentadienyl-9-fluorenyl) ligand (syndiospecific) for the R chirality at metal atom. Corresponding preinsertion intermediates, labeled a in Figures 1.7a,b, are sketched in Figures 1.4 and 1.6a, respectively.

Figure 1.10 Preinsertion intermediates for secondary propene insertion into primary polypropylene chain for (a) isospecific model complex based on (R, R)-coordinatedisopropyl-bis(l-indenyl) ligand and (b) syndiospecific model complex based on isopropyl(cyclopentadienyl-9-fluorenyl) ligand for R chirality at metal atom. Stereoselectivity of isospecific model site is in favor of opposite monomer prochiral faces for primary and secondary insertions (cf. Figures 1.4 and 1.10a). Stereoselectivity of syndiospecific model site is in favor of same monomer prochiral face for primary and secondary insertions (cf. Figures 1.6a and 1.1 Ob).

Site-controlled syndioselectivity of C/-symmetric metallocenes is unprecedented and represents a major achievement of the rational molecular design of single-site catalysts. Recent highly syndioselective metallocenes are listed in Figure The flat fluorenyl ligand has been further spatially extended by substituents at the 2,6- and/or 3,7-... 

Fig. 6.20. Syndiotactic polymerization of propene with isopropyl(l-fluorenyl-cyclopentadienyl) zirconium complexes. See also Fig. 6.19. The cyclopentadienyl ligand above the plane is drawn in full. The fluorenyl ligand below the plane is drawn with dotted lines.

The organolanthanide(II) complexes with tetrahydro-2H-pyranyl- or N-piperidineethyl-functionalized fluorenyl ligands [r 5 r l-C5[ IyOCI I2C 3I Ix]2 Ln and [ri ri -Qd IKINCI I2CII2C13I L]2Ln (Ln = Eu, Yb) were prepared and used in both CL and LA polymerization experiments.64... 

An unsymmetrical Pr sandwich complex containing the donor-functionalized 9-(2-methoxyethyl)fluorenyl ligand, (C0T)Pr(Ci3H8CH2CH20-Me)(THF) was prepared by treatment of dimeric [(COT)Pr(p-Cl)(THF)2]2 with KCi3H8CH2CH2OMe.81... 

It has been established that the replacement of Cp with an indenyl or fluorenyl ligand has important effects on the catalytic properties of these type of complexes. Monoindenyl and monofluorenyl titanium complexes can generally be prepared by employing dehalosilylation (or analogous dehalostannylation) (Scheme 172), and several such complexes have been described. 

Of the three classes designed for elastomeric or plastomeric PP, the most successful seems to be the class of C -symmetric structures. These are based on the bilaterally symmetric fluorenyl ligands, first developed by Ewen,209 and have received a great deal of attention due mainly to three facts (i) they are far simpler to synthesize than the chiral isospecific C2-symmetric metallocenes (ii) they can cover a very broad range of stereoselectivity by structural modification of one ligand only and (iii) due to the presence of two different active sites, they offer a more potent mechanistic tool and intellectual challenge. 

Razavi, A. Bellia, V. Brauwer, Y. D. Hortmann, K. Lambrecht, M. Miserque, O. Peters, L. Belle, S. V. Syndiotactic and Isotactic Specific Metallocene Catalysts with Hapto-flexible Cyclopentadienyl-fluorenyl Ligand. In Metalorganic Catalysts for Synthesis and Polymerization Kaminsky, W., Ed. Springer Berlin, 1999 p 236. 

Related metallocenes utilizing indenyl and fluorenyl ligands have been described. The bis-indenyl and bis-(diisopropyl) indenyl systems can be easily prepared by metathesis from the potassium indenide and the heavier alkaline earth metal iodides. The resulting compounds adopt the familiar bent geometries despite the large steric bulk of the ligands,... 

Four of the catalysts presented in Figure 11 contain unsubstituted cyclopentadienyl, indenyl, or fluorenyl ligands. Of these, 1, 2, and 3 represent well-known examples of catalysts producing syndiotactic, isotactic, and hemiisotactic polypropene at low temperatures, respectively, and we will thus start our analysis of the theoretically derived pentads by comparing... 

There are a few examples of unbridged metallocenes which are stereoselective by site control. Examples have been reported with substituted cy-clopentadienyl, indenyl, and fluorenyl ligands, the latter being apparently the most stereoselective. The biscyclopentadienyl system C2-ITI (Chart 16) produces, at low polymerization temperature (—50 °C), a low molecular weight, low isotactic PP mmmm = 51%) with a double stereodifferentiating mechanism, partly site control (27%, b = 0.96) partly chain-end control (73%, p = 0.79). The related, but much bulkier, rac-[Cp-CH(Ph)CH2(9-BBN)]2ZrCl2 (Q-II-Z) produced at —50 °C a more isotactic PP mmmm = 75%), with predominance of site control (67%, b =... 

Clearly, the model is enantioselective when the propene molecule is inward coordinated (which corresponds to a i chirality at the metal atom for a (R) coordination of the 3-MeCp ligand), since structure A, with a re-coordinated propene, is favored relative to structure B, with a si-coordinated propene, in the framework of the mechanism of the chiral orientation of the growing chain. In fact, structure B is disfavored by repulsive interactions between the growing chain and the fluorenyl ligand. On the contrary, the model is nonenantioselective when the growing chain is... 

Methyl Substituents at Various Positions of the Fluorenyl Ligand in Complexes of the Type (Flu )(Cp)ZrCl2... 

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