Judiciously balancing steric and electronic influences on 2,3-diiminobutane-based Pd(II) complexes in nourishing polyethylene properties

Abstract

A new series of palladium complexes (Pd1–Pd5) ligated by symmetrical 2,3-diiminobutane derivatives, 2,3-bis[2,6-bis{bis(4-FC6H4)2CH}2-4-(alkyl)C6H2N]C4H6 (alkyl = Me L1, Et L2, iPr L3, tBu L4) and 2,3-bis[2,6-bis{bis(C6H5)2CH}2-4-{(CH3)3C}C6H2N]C4H6 L5, have been prepared and well characterized, and their catalytic scope toward ethylene polymerization have been investigated. Upon activation with MAO, all palladium complexes (Pd1–Pd5) exhibited good activities (up to 1.44 × 106 g (PE) mol−1(Pd) h−1) and produced higher molecular weight polyethylene in the range of 105 g mol−1 with precise molecular weight distribution (Mw/Mn = 1.37–1.77). One of the long-standing limiting features of the Brookhart type α-diimine Pd(II) catalysts is that they produce highly branched (ca. 100/1000 C atoms) and totally amorphous polymer. Conversely, herein Pd5 produced polymers having dramatically lower branching number (28/1000) as well as improved melting temperature up to 73.1 °C showing well-controlled linear architecture, and very similar to polyethylene materials generated by early-transition-metal based catalysts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3214–3222.