Pd diimine complexes

O-complexes and the chelate opening prior to the ethylene insertion that seems to be responsible for differences in catalytic activity of the Ni- and Pd-diimine complexes. 

Cationic Pd diimine complexes initiate polymerization of terminal olefins in SCCO2 as the solvent [71], Again, BARF is the anion of choice both for solubility and reactivity reasons. Similarly to the ROMP experiments described above, high turnover rates are observed even after precipitation of the polymer. The solubility of the catalyst was estimated to be in the order of 10" mol L . 

Fig. 9 Energetics (in kcal/mol) of the chain growth and chain isomerization reactions in the ethylene polymerization catalyzed hy the Pd-diimine complex 7 (see Scheme 2). The experimental and theoretical (in parentheses) values are presented. The calculated energies for the chain isomerization reactions (marked with ) were obtained from the model catalyst 1...

Zhang, Y.W. and Ye, Z.B. (2008a) Homogeneous polyhedral oligomeric silsesquioxane (POSS)-suppdiimine complex and synthesis of polyethylenes end-tethered with a POSS nanoparticle via ethylene living polymerization. Chemical Communications, 1178-1180. 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

X-ray analysis shows distorted square planar coordination around Pd. This is the first example of alkyl C-H bond activation with a cationic diimine Pd(II) complex under such mild conditions. 

The results of the MD simulations clearly demonstrate that the insertion starting from the higher energy isomers of the ethylene-chelate complexes in which the chelating bond has been broken have much smaller activation barriers, that are comparable to those observed in ethylene homopolymerization. This, however, does not explain the differences in the copolymerization activity of Pd and Ni-diimine complexes, as the barriers for the ethylene insertion into Ni-alkyl bond are smaller (14.2 kcal/mol) than those for Pd-alkyl bond (16.8 kcal/mol). Thus, it may be concluded that the ethylene insertion following the insertion of the polar monomer is not a crucial factor for the diimine catalyst copolymerization activity. It is the initial poisoning of the catalyst by formation of the... 

Michalak A, Two-reactant Fukui function and molecular electrostatic potential analysis of the methyl acrylate binding mode in the complexes with the Ni- and Pd-diimine catalysts, Chem Phys Lett, 386, 346-350 (2004)... 

In early work on M(diimine)(dithiolate) systems, Miller and Dance (100) examined Ni(II) and Pd(II) complexes in addition to the Pt(II) systems already discussed. While the Ni and Pd complexes exhibit the low-energy solvatochro-mic absorption attributable to a CT- to diimine discussed above, the complexes show no solution emission, which may indicate the importance of the third-row metal ion for efficient intersystem crossing to the triplet CT state and diminished nonradiative decay. In order to probe the effect of metal ion on the excited-state properties of square-planar diimine dithiolate complexes, two Au(III) complexes containing tdt and a diimine or phenylpyridine have been prepared recently and... 

Brookhart and co-workers [79-81] introduced catalysts based largely on chelating, nitrogen-based ligands that are active for the homopolymerization of ethylene and the copolymerization of ethylene with 1-olefins and polar comonomers (31). Ni, Co, Fe or Pd are used as late transition metals. The diimine ligands have big substituents to prevent 6-hydride elimination. Ni(II) or Pd(II) complexes form cations by combination with MAO and polymerize ethylene to highly branched polymers with molecular weights up to one million. The activities reach TON... 

In both complexes, llb,d, the Pd-I bond trans to the phosphorus atom (Pdl—12 in 11b and Pdl-Il in lid) is longer (0.08 and 0.09 A) than the Pd-I bond trans to the nitrogen atom, which might be attributed to the larger trans influence of the phosphorus compared to nitrogen (imine and pyridine) [45]. In the solid state one of the o-aryl substituents in complex llb,d (methyl in the case of 11b and isopropyl in the case of lid) is oriented above/below the coordination plane. A connection between shielding of the metal center along the z-axis and chain transfer reactions was found for several diimine complexes [22 c, 33 b, 41, 42 c]. 

At this juncture, in order to facilitate comparisons of the families of lu-minophores described in this account, a table illustrating the correlation between the metal-metal distances and photophysical properties of relevant cy-clometalated diimine Pt(II)/Pd(II) complexes is provided (Table 3). 

Table 3 Comparison of structural and photophysical data for cyclometalated diimine Pt(II)/Pd(II) complexes... 

Scheme 2. Mechanism for Ethylene Polymerization and Polymer Branch Formation with Ni md Pd a-Diimine Complexes ...

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