No 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.

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.