Nickel-based olefin polymerization and oligomerization catalysts have attracted considerable recent attention. 1,2 Depending on the ancillary ligand framework, these catalysts participate in chain-walking reactions, 3,4 tolerate polar functionalities on the monomer, 5 and may even be used in water. 6 These properties allow for the synthesis of materials with unique topologies 7 and could enable new industrial processes. 2 During our efforts at developing tandem catalytic processes, 8 we discovered that the reactivity of SHOP-type catalysts such as [(C 6 H 5 ) 2 PC 6 H 4 C(O)O-κ 2 P,O]Ni(η 3 -CH 2 CMeCH 2 ) 9 increases considerably upon addition of B(C 6 F 5 ) 3 . Carbonyl coordination to the borane gives [(C 6 H 5 ) 2 PC 6 H 4 C(O-B(C 6 F 5 ) 3 )O-κ 2 P,O]Ni(η 3 -CH 2 CMeCH 2 ) and removes electron density from nickel. This "activation" by action of a Lewis acid on a site removed from the monomer insertion trajectory prompted our attention. The more common situation reduces to methyl abstraction and coordination of the resulting borate anion. 10 Borate dissociation from the metal is a generally accepted requirement for olefin insertion. 11 It occurred to us that metal activation by formation of carbonyl adducts could form the basis of a new strategy for designing novel nickel olefin polymerization catalysts such as 1-3. Resonance structures I and II illustrate the loss of electron density at nickel.R-Iminocarboxamide ligands were chosen because they can be readily prepared and because the size of the substituents on nitrogen can be varied to modulate steric effects. Of interest to us was to control the size of the substituents on the pseudoaxial sites, since blocking these sites in other nickel catalysts reduces chain transfer to the monomer. 1,12 The η 3 -benzyl fragment was selected, instead of the more frequently used methallyl, because it displays faster rates of initiation. 13 Typical Schiff-base condensation 14 of primary arylamines with N-aryl pyruvamides 15 yields R-iminocarboxamides. As shown in Scheme 1, carboxamide deprotonation with 1.0 equiv KH, followed by reaction with Ni(η 3 -CH 2 C 6 H 5 )Cl(PMe 3 ), 16 results in the clean formation of the R-iminocarboxamide complexes 4 (R 1 ) R 2 ) H), 5 (R 1 ) CHMe 2 , R 2 ) H), and 6 (R 1 ) R 2 ) CHMe 2 ). Recrystallization from benzene by slow diffusion of pentane vapor at room temperature (4 and 5), or pentane at -30°C (6), affords analytically pure 4-6 in 70-80% yields.Structural characterization of 4 ( Figure 1) reveals a distorted square-planar geometry (interplane angle of NNiN and CNiP planes: 42.2°) with a trans relationship between PMe 3 and the imine nitrogen. The distance between Ni and the carboxamide-N is shorter (1.936(2) Å) than that between Ni and the imine-N (2.001(3) Å); the C-O distance (1.243 (4) Å) is consistent with a double bond between these two atoms. In 6, it is the carboxamide oxygen that coordinates to nickel (Figure 2), and the ligand environment is strictly square-planar (interplane angle of NNiO and CNiP planes: 4.3°). Th...

The products obtained with the system {[(ArNC(Me))2C5H3N]FeCl2}/MAO (Ar = 2-C6H4(Et)) (1) and the ones obtained by the use of 1 in conjunction with Me2SiInd2ZrCl2/MAO (2) or EtInd2ZrCl2/MAO (3) were completely characterized by 1H NMR and 13C NMR. Catalyst 1 gives mainly linear α-olefins of molecular weights close to 2000 g/mol and a low amount of alkanes. The use of 1 with 2 or 3 using only ethylene as monomer gives branched polyethylene with ethyl, butyl, and mainly long branches. Some amount of unreacted α-olefin was also found in some cases, especially in reactions where a high ratio Fe to Zr was used.

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