N-Substituted Iminocaprolactams as Versatile and Low Cost Ligands

Article Cite This: Organometallics XXXX, XXX, XXX-XXX

pubs.acs.org/Organometallics

N‑Substituted Iminocaprolactams as Versatile and Low Cost Ligands in Group 4 Metal Initiators for the Living Coordinative Chain Transfer Polymerization of α‑Olefins Jia Wei, Leila M. Duman, Daniel W. Redman, Brendan L. Yonke, Peter Y. Zavalij, and Lawrence R. Sita* Laboratory for Applied Catalyst Science and Technology, Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States S Supporting Information *

ABSTRACT: A new structurally diverse ligand for metal complexes, the (κ2-N,N)iminocaprolactam group, that can be obtained in large bulk quantities from inexpensive and readily available starting materials, is introduced. In the present report, the ability of this family of ligands to provide a viable substitute for the acyclic amidinate moiety of a class of cationic monocyclopentadienyl, amidinate (CPAM) group 4 metal initiators for the living coordination polymerization (LCP) and living coordinative chain transfer polymerization (LCCTP) of α-olefins is documented through the synthesis of (η5-C5Me5)Hf[(R)NimcapN](Me)2 [R = benzyl (1), CH2(1-naphthyl) (2), and tert-butyl [C(CH3)3] (3)] as preinitiators for the (stereoselective) LCP and LCCTP of propene.

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INTRODUCTION

monocyclopentadienyl hafnium initiators for (stereoselective) LCP and LCCTP.

The living coordination polymerization (LCP) of ethene, αolefins, and α,ω-nonconjugated dienes, in which chain-growth propagation proceeds through repetitive migratory insertions of monomer at an active metal species in the absence of irreversible chain-termination, can provide access to a wealth of new “precision polyolefins” with a previously unimaginable degree of control over polymer architecture, molecular weight distribution, and, more increasingly, the solid-state bulk properties of these materials.1 In addition, the more recent development of living coordinative chain transfer polymerization (LCCTP), which introduces multiple equivalents of a relatively inexpensive main-group-metal alkyl, such as diethylzinc (ZnEt2) or triethylaluminum (AlEt3), as the source for a large population of “surrogate” chain-growth sites, can be used to amplify product yield through rapid and reversible chain transfer that occurs between active and surrogate sites.2−6 Indeed, with LCCTP, it is now possible to obtain kilogram quantities of low molecular weight (e.g.,