title: Chelate bis(imino)pyridine cobalt complexes: synthesis, reduction, and evidence for the generation of ethene polymerization catalysts by Li+ cation activation.
abstract: Treatment of the bis(iminobenzyl)pyridine chelate Schiff-base ligand 8 (ligPh) with FeCl2 or CoCl2 yielded the corresponding (ligPh)MCl2 complexes 9 (Fe) and 10 (Co). The reaction of 10 with methyllithium or "butadiene-magnesium" resulted in reduction to give the corresponding (ligPh)Co(I)Cl product 11. Similarly, the bis(aryliminoethyl)pyridine ligand (ligMe) was reacted with CoCl2 to yield (ligMe)CoCl2 (12). Reduction to (ligMe)CoCl (13) was effected by treatment with "butadiene-magnesium". Complex 13 reacted with Li[B(C6F5)4] in toluene followed by treatment with pyridine to yield [(ligMe)Co+-pyridine] (15). The reaction of the Co(II) complexes 10 or 12 with ca. 3 molar equiv of methyllithium gave the cobalt(I) complexes 16 and 17, respectively. Treatment of the (ligMe)CoCH3 (17) with Li[B(C6F5)4] gave a low activity ethene polymerization catalyst. Likewise, complex 16 produced polyethylene (activity = 33 g(PE) mmol(cat)(-1) h(-1) bar(-1) at room temperature) upon treatment with a stoichiometric amount of Li[B(C6F5)4]. A third ligand (lig(OMe)) was synthesized featuring methoxy groups in the ligand backbone (22). Coordination to FeCl2 and CoCl2 yielded the desired compounds 23 and 24. Reaction with MeLi gave (ligOMe)CoMe (25/26). Treatment of 25/26 with excess B(C6F5)3 gave the eta6-arene cation complex 27, where one Co-N linkage was cleaved. Activation of 25/26 with Li[B(C6F5)4] again gave a catalytically active species.
authors.affiliation: Organisch-Chemisches Institut Universität Münster, Corrensstr. 40, D-48149 Münster, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Kleigrewe
authors.forename: Winfried
authors.initials: W
authors.lastname: Steffen
authors.forename: Tobias
authors.initials: T
authors.lastname: Blömker
authors.forename: Gerald
authors.initials: G
authors.lastname: Kehr
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Birgit
authors.initials: B
authors.lastname: Wibbeling
authors.forename: Gerhard
authors.initials: G
authors.lastname: Erker
authors.forename: Julia-Christina
authors.initials: JC
authors.lastname: Wasilke
authors.forename: Guang
authors.initials: G
authors.lastname: Wu
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Bazan
mesh_terms: D002384:Catalysis; D002412:Cations / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005030:Ethylenes / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008094:Lithium / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*
chemical_list: D002412:Cations; D002614:Chelating Agents; D005030:Ethylenes; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D003035:Cobalt; C036216:ethylene; D008094:Lithium; D007501:Iron