Polyketones metal complexes

Polyisothiouronium group chelating resins mineral processing, 6,826 Polyketones metal complexes, 2, 399 Poly(L-lysine) metal complexes, 2, 764 Polymerization solid state, 1, 470 Polymers... 

Pd complex-catalyzed copolymerization of alkene and CO affords the polyketones via alternating insertion of the two monomers [166, 167]. The polymer growth involves migratory insertion of CO into the metal-carbon bond as a crucial step, which is unique to the late transition metal complexes such as Ni, Pd, Rh, and Co. The copolymerization of allenes and methylenecydopropanes with CO has attracted much less attention than the alkene-CO copolymerization, although it would provide further functionalized polyketones due to the dual functionality of the dienes and the derivatives. 

Another area of considerable interest in polynuclear metal complex chemistry for which the -polyketones seem well suited is that of mixed metal and mixed valence complexes. When one is seeking fundamental data on how the molecular structure and properties of such compounds relate to bulk properties, it is not sufficient to be content with uncertainties concerning purity and the positions of the different ions. In this paper we report on a systematic approach to the preparation of some heteronuclear, molecular chelates, i,e, molecules containing two or more... 

Late transition-metal complexes can also polymerize nonpolar and polar comonomers, such as alkyl acrylates, acrylonitrile, or carbon monoxide. Polyketones have been efficiently produced through CO-ethylene copolymerizations [46],... 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

Since 1985, several thousands of publications have appeared on complexes that are active as catalysts in the addition of carbon monoxide in reactions such as carbonylation of alcohols, hydroformylation, isocyanate formation, polyketone formation, etc. It will therefore be impossible within the scope of this chapter to review all these reports. In many instances we will refer to recent review articles and discuss only the results of the last few years. Second, we will focus on those reports that have made use explicitly of coordination complexes, rather than in situ prepared catalysts. Work not containing identified complexes but related to publications discussing well-defined complexes is often mentioned by their reference only. Metal salts used as precursors on inorganic supports are often less well defined and most reports on these will not be mentioned. 

Most researchers currently agree that the hydrido mechanism is more common than the alkoxycarbonyl path in the alkoxycarbonylation of alkenes with palladium systems. However, carbalkoxy complexes are putative intermediates in carbonylation reactions giving succinates and polyketone diesters, with metals like Co, Rh, or Pd.137... 

Polynuclear complexes with more than two metal ions have been prepared with polyketone ligands but no such complexes have been reported with V02+. With the tetraketone l,l -(2,6-pyridyl)-bis-l,3-butanedione (H2L), several polynuclear complexes have been prepared including [(VO)2(L)2] for which jj,Tc = 1.21 BM was obtained.908... 

Triketones and similar polyketones exhibit keto-enol tautomerism and have been found to coordinate to one or more metal atoms (24). Such complexes can bring metal atoms in close proximity, resulting in interesting magnetic properties (see Magnetism of Transition Metal Ions). 

These complexes result from the coordination of tri-, tetra- or polyketonates to two or more metal centers (138-140). Because these topics have been reviewed widely and recently and, in addition, the methods of synthesis are not different from those outlined above, only a few of them will be discussed. 

However, there is also a major difference between the two types of catalysts. The olefin polymerization metallocene catalysts (cf. Section 2.3.1.1) are much more electrophilic, due to the higher positive charge of the metal ion, than the pal-ladium(II) complexes discussed above. For polyketone formation, electrophilicity needs to be balanced so that olefins can still compete with carbon monoxide for coordination to the metal cation. 

The substitution of nickel for palladium catalyst precursors has, in principle, two advantages the lower price of the metal and the lower tendency to plate. The effectiveness of nickel in the carbonylation of ethene to low molecular weight polyketones has been known for a long time [4]. Only recently, however, have nickel catalyst precursors with a reasonably high catalytic activity been discovered. The newest compounds are nickel complexes, which are modified by semicorrine-type ligands (Scheme 8.10). 

As mentioned above and as demonstrated by model studies using various acetyl complexes, the insertion of styrene usually takes place with secondary regiochemistry [8]. However, styrene was found to insert with both primary and secondary regiochemistry into the metal-acetyl bond of a complex obtained by carbonylation of 66. It is very remarkable that primary regiochemistry only was observed for the insertion in a homologous complex, in which a polyketone chain (CH ),CO CH(CH ),)CH2C()[ i--,) was substituted for the acetyl ligand. Thus, it was proposed that, for this catalytic system, primary insertion of styrene is responsible... 

Polymerization of 7V-vinylcarbazole catalyzed by dimethylglyoxime complexes of different metals immobilized on PVC follows the cationic mechanism. Lewis acids immobilized in a volume of swollen polymer gel catalyze cationic polymerization and oligomerization of vinyl ethers, etc. Cationic complexes of Pd(II) bound to modified PS initiate alternative copolymerization of fluorinated olefins (C F2 +i)(CH2)mCH=CH2 with carbon monoxide [112,113]. The product thus obtained was polyspiroketal rather than polyketone. 

Since this finding, a large variety of transition-metal-based catalysts have been reported for the production of perfectly alternating aliphatic polyketones (17-27). Particularly suitable systems include palladium(II)- or nickel(II)-based complexes modified with a neutral or anionic bidentate chelating ligand and weakly coordinating anions X (such as OTs, OTf, TEA, BF4 and tetra-arylborates) (2,3,13). 

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