Synthesis of Highly Branched Polyolefins Using Phenyl Substituted α-Diimine Ni(II) Catalysts

A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr2 (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me2-4-PhC6H2 (C1); Ar = 2,4-Me2-6-PhC6H2 (C2); Ar = 2-Me-4,6-Ph2C6H2 (C3); Ar = 4-Me-2,6-Ph2C6H2 (C4); Ar = 4-Me-2-PhC6H3 (C5); Ar = 2,4,6-Ph3C6H2 (C6)), were synthesized and characterized. Upon activation with either diethylaluminum chloride (Et2AlCl) or modified methylaluminoxane (MMAO), all Ni(II) complexes showed high activities in ethylene polymerization and produced highly branched amorphous polyethylene (up to 145 branches/1000 carbons). Interestingly, the sec-butyl branches were observed in polyethylene depending on polymerization temperature. Polymerization of 1-alkene (1-hexene, 1-octene, 1-decene and 1-hexadecene) with C1-MMAO at room temperature resulted in branched polyolefins with narrow Mw/Mn values (ca. 1.2), which suggested a living polymerization. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature and types of monomers.

The molecular structures of complexes C1 and C5′ were confirmed by single-crystal X-ray diffraction and the corresponding ORTEP diagrams are shown in Figure S1. Crystal data, data collection, and refinement parameters are listed in Table S1. Selected bond distances and angles are summarized in Table S2.   Figure S2. Cell structure of C1 parallel to the bis(imino)acenaphthene unit.

Synthesis and Characterizations of Complexes C1-C7
The synthesis of ligands L, L1-L7 and their complexes Pd-Cat., C1-C7 are outlined in Scheme S1. After the protection of the amino group by acetic acid, the aniline derivatives were brominated. The Suzuki-coupling reaction of the bromoaniline derivatives and phenylboronic acid obtained with a Pd(II) catalyst (Pd-Cat.) in PEG-400/H2O led to the corresponding phenyl-substituted aniline derivatives 1-6. The ligands L1-L7 were prepared by the condensation of two equivalents of the appropriate aniline with one equivalent of acenaphthoquinone, in the presence of a formic acid catalyst. The reaction of equimolar amounts of NiBr2(DME) and the α-diimine ligands L1-L7 in CH2Cl2 led to the displacement of 1,2-dimethoxyethane and afforded the Ni(II) complexes C1-C7 as a moderately air-stable deep red microcrystalline solid in good yields, respectively. The corresponding palladium dichloride complex (Pd-Cat.) is accessible by the reaction of the ortho-sec-phenethyl substituted chiral ligand L with (CH3CN)2PdCl2 in CH2Cl2 at ambient temperature. Compounds L1-L7 were well characterized by IR, 1 H NMR, 13 C NMR spectroscopy and elemental analysis. Scheme S1. Synthesis of α-diimine ligands L, L1-L7 and their complexes Pd-Cat., C1-C7.
The new organic compounds were well characterized by 1 H NMR and 13 C NMR (see below).

Calculation of the Degree of Branching
The degree of branching (B) was estimated by 1 H NMR spectroscopy and was corrected for end groups as follows (S1): Branching degree, the number of methyl carbon in every 1000 carbons, CH3, CH2, CH refer to the intensities of the methyl, methylene and methine resonances in 1 H NMR spectra.

Calculation of ω,1-Insertions
The fraction of ω,1-insertions was calculated using the following equation reported by Brookhart et al. [1].
where B is the total branching calculated by Equation (S1), ω is the number of carbon atoms in the monomer.
Assignments of the 13 CNMR spectra and equations for the quantitative analysis of the polyolefins under investigation, according to Equation (S3) reported by Azoulay et al. [2]. Chemical shift and assignment of the peak listed in the Table S4 are marked in the spectrum ( Figure S12).  Table 1).  Figure S12; Note on labels: for xBn Bn is a branch of length n carbons, x is the carbon being discussed, and the methyl at the end of the branch is numbered 1. Thus, the second carbon from the end of a butyl branch is 2B4. xBn+ refers to branches of length n and longer. (Tables 1 and 2) NMR spectra of the polyethylenes prepared by C1−C7 (see Figures S13−S21): Figure S13. 1 H NMR spectra of the polyethylenes obtained with C1-Et2AlCl (entries 3 and 7−9, Table 1). Figure S14. 1 H NMR spectra of the polyethylenes obtained with C1-MMAO (entries 10−14, Table 1). Figure S15. 1 H NMR spectra of the polyethylenes obtained with C2−C7/MMAO (entries 15−20, Table 1). Figure S16. 13 C NMR spectra of the polyethylene obtained with C1-Et2AlCl at 40 °C (entry 7, Table 1).