Catalyst/Cocatalyst Nuclearity Effects in Single-Site Polymerization. Enhanced Polyethylene Branching and α-Olefin Comonomer Enchainment in Polymerizations Mediated by Binuclear Catalysts and Cocatalysts via a New Enchainment Pathway

Abstract

The binuclear "constrained geometry catalyst" (CGC) (mu-CH2CH2-3,3'){(eta5-indenyl )[1-Me2Si(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2; Zr2] and the trityl bisborate dianion (Ph3C+)2[1,4-(C6F5)3BC6F4B(C6F5)3]2- (B2) have been synthesized to serve as new types of multicenter homogeneous olefin polymerization catalysts and cocatalysts, respectively. Additionally, the complex [1-Me2Si(3-ethylindenyl)(tBuN)]ZrMe2 (Zr1) was synthesized as a mononuclear control. For the bimetallic catalyst or bisborate cocatalyst, high effective local active site concentrations and catalyst center-catalyst center cooperative effects are evidenced by bringing the catalytic centers together via either covalent or electrostatic bonding. For ethylene homopolymerization at constant conversion, the branch content of the polyolefin products (primarily ethyl branches) is dramatically increased as catalyst or cocatalyst nuclearity is increased. Moreover, catalyst and cocatalyst nuclearity effects are approximately additive. Compared to the catalyst derived from monometallic Zr1 and monofunctional Ph3C+B(C6F5)4- (B1), the active catalyst derived from bimetallic Zr2 and bifunctional B2 produces approximately 11 times more ethyl branches in ethylene homopolymerization via a process which is predominantly intradimer in character. Moreover, approximately 3 times more 1-hexene incorporation in ethylene + 1-hexene copolymerization and approximately 4 times more 1-pentene incorporation in ethylene + 1-pentene copolymerization are observed for Zr2 + B2 versus Zr1 + B1.

Nuclearity and cooperativity effects in binuclear catalysts and cocatalysts for olefin polymerization

“…2) (14)(15)(16)(17)(18)(19). These complexes were accessed via a protodeamination protocol by using the mono-or bifunctional CGCH 2 ligands and driven to completion by continuous removal of the volatile HNMe 2 coproduct (Fig.…”

“…The sequence of first introducing Zr(NMe 2 ) 2 then Ti(NMe 2 ) 2 is used because the former ligand substitution process is far more rapid and more selective. For control experiments, monometallic CGC complexes Zr 1 and Ti 1 were synthesized via methodologies similar to those for the bimetallic complexes (14,17) (Fig. 20, which is published as supporting information on the PNAS web site).…”

“…Fig. 4 shows the solid-state structure of bimetallic bis(dimethylamido) Zr complex EBICGC[Zr(NMe 2 ) 2 ] 2 (EBI ϭ ethylenebisindenyl), the precursor to Zr 2 (14). The data …”

“…A variety of binuclear cocatalysts have been synthesized, several of which are shown in Fig. 6 (14,17,(20)(21)(22). For the synthesis of bisborane BN 2 , the metathesis of fluoroaryl tin reagents with a perfluorophenylborane precursor has proven to be an effective and general approach to synthesizing binuclear bisborane cocatalysts, as shown in Fig.…”

Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes

“…The cation of 8Al was also unstable at room temperature and was further transformed into a mixture of compounds in which the chloro-bridged compound (10) was identified. 36 The same reaction employing [Ph 3 C][B(C 6 F 5 ) 4 ] resulted in decomposition of the starting materials.…”