¹³C and 2D NMR Analysis of Propylene Polymers Made with α-Diimine Late Metal Catalysts

Abstract

Late transition metal catalysts bearing R-diimine ligands allow ethylene and R-olefin homoand copolymerizations to polyolefins with unprecedented structures. The polypropylenes made with these new late metal catalysts have very complex microstructures that include combinations of features not seen in any known polypropylenes. These unusual structures include long branches, branches on branches including isobutyl branches, and moderate highly variable levels of 1,3-enchainment leading to runs of methylenes in the backbone of many different well-defined lengths. These features vary with the nature of the catalyst used for polymerization and with the polymerization conditions. Many of the polypropylenes are made primarily by 1,2-insertions to give syndiotactic placements via chain end control. A mechanistic description of catalyst behavior has been developed to explain these observed microstructures.

Agostic interactions in transition metal compounds

“…Cationic nickel(II) and palladium(II) complexes of type {[ 2 -ArNϭC(R)C(R)ϭNAr]MR} ϩ are highly active late metal catalysts for polymerization of a broad spectrum of olefinic monomers (80)(81)(82)(83)(84). The polymer microstructures obtained by using these systems are unique and quite different from those obtained from polymerizations by using early metal catalysts.…”

Highly regioirregular polypropylene from asymmetric group 4 anilide(pyridine)phenoxide complexes

“…13 There are examples of post-metallocene catalysts that appear to propagate exclusively via a 2,1-insertion mechanism, 14 but to the best of our knowledge this is the only early metal catalyst that shows so little apparent preference for 1,2-vs. 2,1-insertions; 15 such low regiocontrol is more commonly observed with late metal polymerization catalysts that can undergo ''chain running''. 16 A half-metallocene system was reported to incorporate 2,1-insertions on the order of 10% at 25 1C (the percentage decreased at lower temperatures). The relative steric openness of the system was offered as a possible explanation for the higher frequency of inversion relative to metallocene polymerization catalysts.…”

Complex Branched Polyolefin Generated from Quasi-living Polymerization of 4-Methyl-1-pentene Catalyzed by α-Diimine Palladium Catalyst

“…DEPT experiments were further carried out to precisely assign peaks. Combining 13 C NMR and DEPT spectra (see On the basis of our previous resonance assignments of poly(4MP) obtained by a-diimine nickel catalyst [11] and reference to model compound data found in the literatures, [17,18] methyl branches and isobutyl branches can be assigned. In addition, 2,4-dimethylpentyl branch can be confirmed by the appearance of two characteristic peaks at 47.…”