α-Iminocarboxamide Nickel Complexes:  Synthesis and Uses in Ethylene Polymerization

Abstract

A series of nickel complexes containing R-iminocarboxamide, η 1 -benzyl, and PMe 3 ligands were synthesized to identify structural features of neutral Ni complexes that are employed in ethylene polymerization and ethylene/functionalized norbornene copolymerizations. Variations in steric bulk on aryl substituents in the R-iminocarboxamide framework were used to probe N,N-versus N,O-binding modes. When the steric bulk is sufficiently large, as in 4), both, N,O-and N,N-bound modes can be obtained and isolated; the N,N structure is the thermodynamic product. N,N products are observed with smaller ligands, as in 6). Ethylene polymerization, upon activation with Ni(COD) 2 , is observed only with the N,O-bound species. NMR spectroscopy shows that addition of Ni(COD) 2 to 5 and 6 results in removal of the phosphine and the formation of an η 3 -benzyl fragment. Furthermore, the phosphine-free complex 7) is also inactive toward ethylene polymerization. These observations suggest that ethylene polymerization is preferentially initiated by nickel complexes with N,O-bound R-iminocarboxamide ligands.

Highly dispersed clay–polyolefin nanocomposites free of compatibilizers, via the in situ polymerization of α-olefins by clay-supported catalysts

“…Thus [N-(2, 6-diisopropylphenyl)-2 -(2, 6-diisopropylphenylimino)propanamidato-k 2 -N,N]Ni(Z 3 -CH 2 Ph), 1, can be activated for ethylene polymerization by binding a Lewis acid such as B(C 6 F 5 ) 3 at the carbonyl group on the ligand backbone, generating a Zwitterionic adduct. [19][20][21] An analogous activation mechanism is proposed for the complex interacting with the surface of clay, Scheme 1.…”

A zwitterionic nickel–olefin initiator for the preparation of high molecular weight polyethylene

“…1 H and 13 C NMR spectra were calibrated using signals from the solvent and are reported downfield from tetramethylsilane referenced to residual solvent 1 H and 13 C signals. 11 B NMR, 19 F NMR and 31 P NMR spectra were calibrated and reported downfield from external BF 3 AE OEt 2 , CFCCl 3 and H 3 PO 4 , respectively. Elemental analyses were performed by Analytic Lab, Marine Science Institute, University of California, Santa Barbara.…”

“…The activity increases with temperature and at 75°C (entries 3 and 4) it is comparable to those of cationic diimine nickel initiators [2]. The polymers formed at high temperature have broader PDIs, increased branching in the backbone (23 branches/1000 carbons) and lower melting points [1,19]. No reaction is observed when 1 is used alone (entry 5).…”

Olefin Polymerization with Non-metallocene Catalysts (Late Transition Metals)

“…The reaction with Ni(cod) 2 cocatalyst affords the phosphine-free intermediate, which catalyzes quasi-living polymerization of ethylene as well as copolymerization of ethylene with functionalized norbornene [121,122]. Bulky aryl groups on both the nitrogens favor formation of the N,O-coordinated complex, which is active for ethylene polymerization [123,124]. On the other hand, the complex with less bulky aryl group on either or both of the nitrogens prefers the N,N-coordinated structure, which shows low activity for ethylene oligomerization.…”