Sterically Demanding Iminopyridine Ligands

Abstract

Two sterically demanding iminopyridine ligands, (2,6‐diisopropylphenyl)[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐ylmethylene]amine and (2,6‐diisopropylphenyl)[6‐(2,6‐dimethylphenyl)pyridin‐2‐ylmethylene]amine, were prepared by a two‐step process: first, condensation of 6‐bromopyridine‐2‐carbaldehyde with an equimolecular amount of 2,6‐diisopropylaniline, and second, Kumada‐type coupling of in‐situ‐formed Grignard compounds of 1‐bromo‐2,6‐dimethylphenyl and 1‐bromo‐2,4,6‐triisopropylphenyl. Dichlorido complexes of the ligands were synthesized starting from FeCl2, [PdCl2(cod)], [NiCl2(dme)], and CoCl2 (cod = 1,5‐cyclooctadiene, dme = dimethoxyethane). X‐ray crystal structure analyses of a Fe, Pd, and Co complex were determined. Ethylene polymerization/oligomerization behavior of the dichlorido complexes after activation with methylaluminoxane or triethylaluminum was studied. Ethylene dimerization selectivity greater than 95 % was observed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization

“…Scheme 1 N,N-bi-dentate iron and cobalt complexes 24 Kempe et al have investigated the 6-aryl-substituted N,Nbi-dentate iron and cobalt complexes 6-9 (Scheme 2) for ethylene oligomerization. 31 In the case of the iron complexes 6 and 8, scant activity was observed (entries 1 − 4, Table 2), 50 whereas systems 7 and 9 exhibited high selectivity towards 1-butene (entries 5 − 8, Table 2). High ethylene dimerization selectivities were also observed for iminopyridine complexes bearing less sterically demanding substituents at the pyridine 6-position.…”

“…High ethylene dimerization selectivities were also observed for iminopyridine complexes bearing less sterically demanding substituents at the pyridine 6-position. 31 Upon activation with triethylaluminium (TEA) 55 rather than methylaluminoxane (MAO), reduced activity was observed and whilst the formation of polymeric by-products was suppressed, the dimerization selectivity increased to over 95 % (entries 5 − 8, Table 2). The results obtained with cobalt complexes 7 and 9 were similar to (nearly as good as) the 60 results observed by Bianchini and coworkers, who observed for iminopyridine cobalt complexes (activated with MAO) bearing a 6-phenyl or 6-naphthyl substituent on the pyridine ring, the formation of oligomerization products and butenes.…”

Olefin oligomerization, homopolymerization and copolymerization by late transition metals supported by (imino)pyridine ligands

“…The vast majority of 2-organylimino-pyridyl ligands are straightforwardly prepared by condensing 2-acetyl or 2-formyl-pyridine systems with an equivalent amount of the proper amine [13][14][15][16][17][18] or aniline [2,3,[5][6][7]16,[19][20][21][22][23][24][25][26][27][28][29][30], possibly in the presence of an acid cocatalyst (Scheme 2a). The synthesis of 6-organyl-2-iminopyridyl ligands generally requires a more complex procedure and the Schiff-base condensation step just concludes the synthetic path.…”

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

“…[30] Iminopyridines are versatile bidentate ligands that can be easily prepared by condensation of the appropriate pyridine carbonyl compound with the desired amine. [31][32][33] Post-functionalization can also be performed by using,f or example, Stille [34] or Kumada [35] coupling at the pyridine ring. In catalysis, the relevant late transition metal complexes have been used, amongst others, in alkene oligo-and polymerization, [36] and in af ew examples for polyketone synthesis.…”