Diimine ligands, catalysis with

Chiral salen ligands are diimines of salicylaldehydes with chiral diamines, usually cyclohexane-1,2-diamine (salen Hgands 1) or 1,2-diphenylethylene-diamine (salen ligands 2). The most widely used salen ligand in homogeneous catalysis is probably Jacobsen s ligand (la. Fig. 2), which is commercially available and hence has been used as reference to compare the results of im-... 

In 1996, Brookhart and co-workers developed a remarkable class of Pd complexes with sterically encumbered diimine ligands (Scheme 4, S4-1, S4-2, S4-4, and S4-5). These examples are capable of mediating the co-polymerization of ethylene with methyl acrylate (MA) to furnish highly branched PE with ester groups on the polymer chain ends by a chain-walking mechanism (Scheme 10). " This represents the first example of transition metal-catalyzed ethylene/MA co-polymerization via an insertion mechanism. The mechanism for co-polymerization is by 2,1-insertion of MA and subsequent chelate-ring expansion, followed by the insertion of ethylene units. The discovery of these diimine Pd catalysts has stimulated a resurgence of activity in the area of late transition metal-based molecular catalysis. Recently, the random incorporation of MA into linear PE by Pd-catalyzed insertion polymeriza-... 

Inspired by the observation of efficient hydrogenation catalysis with iron compounds bearing redox-active tridentate ligands, our laboratory also explored related chemistry with reduced iron compounds with bidentate chelates [92]. Aryl-substituted a-diimines were attractive supporting ligands due to their ease of synthesis, estabUshed one- and two-electron redox-activity [92-95] and precedent in iron-catalyzed C-C bond forming reactions [96-98]. 

Organozinc diiminates of various ligand platforms (particularly /2-diketiminates (BDIs)) have been used extensively in catalysis, especially for the polymerizations of lactides and epoxides and the co-polymerization of epoxides with carbon dioxide. 

One of the more extraordinary recent developments in nickel and palladium polyalkene catalysis has been the development of a-diimines with bulky substituents as ligands in nickel and palladium complexes. When bulky aryl groups are used (R = isopropyl), these catalysts polymerize ethylene with high activities to high molecular weight highly branched... 

Alkenes and/or alkynes can be dimerized, telomerized, and polymerized under palladium-catalysis. In an effort to copolymerize polar co-monomers, Johnson et al. investigated catalysts based upon palladium. These catalysts were referred to as postmetallocene catalysts. They were based upon complexes bearing bulky, neutral, alpha-diimine (or diketimine) ligands. They have been commercialized as DuPont s Versipol olefin polymerization system. The commercial synthesis of 1-octene (starting in 2007) is a palladium-catalyzed telomerization of butadiene with methanol. ... 

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