Zwitterionic Trivalent (Alkyl)Lanthanide Complexes in Ziegler-type Butadiene Polymerization

Date
2019-01-01
Authors
Rossini, Aaron
Schmidt, Bradley
Pindwal, Aradhana
Venkatesh, Amrit
Sadow, Aaron
Ellern, Arkady
Rossini, Aaron
Sadow, Aaron
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Abstract

The organolanthanide complexes Ln{C(SiHMe2)3}3 (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) react with one or two equiv. of B(C6F5)3 to yield the well-defined zwitterionic species Ln{C(SiHMe2)3}2HB(C6F5)3 (Ln = La, 2a; Ce, 2b; Pr, 2c; Nd, 2d) or LnC(SiHMe2)3{HB(C6F5)3}2 (Ln = La, 3a; Ce, 3b; Pr, 3c; Nd, 3d), respectively. These complexes are shown to contain labile, bridging Si–H⇀Ln and o-F->Ln interactions based upon the observation of low one-bond silicon-hydrogen coupling constants (1JSiH) in 1H NMR spectra of 2a and 3a, the presence of one set of C6F5 signals in the 19F NMR spectra of 2a and 3a, the detection of only m-F and p-F resonances in 19F NMR spectra of 2b-d and 3b-d, two νSiH bands in IR spectra of 2a-d, and X-ray crystallography analyses of 2b and 3d. In addition, a hexametertoluene molecule is coordinated to neodymium in 3d. Reactions of 1a and (AlMe3)2 yield labile adducts with an approximate stoichiometry of 1a·3AlMe3. Exchange between free and bound AlMe3 groups was observed in EXSY NMR experiments with greater than 3 equiv. of AlMe3. Compounds 2a-d and 3a-d, in the presence of AliBu3, are precatalysts for polymerization of butadiene. The neodymium alkyl 3d has the highest activity of the series, and its performance is consistent with chain transfer reactions with AliBu3.

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<p>This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in <em>ACS Catalysis</em>, copyright © American Chemical Society after peer review. To access the final edited and published work see DOI: <a href="http://dx.doi.org/10.1021/acscatal.8b04025" target="_blank">10.1021/acscatal.8b04025</a>.</p>
Keywords
polybutadiene, neodymium alkyl, polymerization, Ziegler catalyst, rare earth
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