Cobalt catalysts coordination polymers

Colloidal metal clusters, which offer a high surface area for better activity, have been stabilized by polymers. Thus, a homogeneous dispersion of a cobalt-modified platinum cluster was stabilized by a coordinating polymer, poly(/V-vinyl-2-pyrrolidone).74 Addition of the cobalt(II) [or iron(III)] doubled the activity and increased the selectivity from 12 to 99% when the catalyst was used to reduce cin-namaldehyde (5.23). 

Among the earliest studies was that of Moffat (105). Poly-2-vinylpyri-dine, cross-linked with 4-8% divinylbenzene, was used as the coordinating support. The amount of cross-linking was found to be critical too little gave a soluble polymer, while too much gave an intractable material which absorbed little metal. Cobalt was used as the catalyst, and the reaction was conducted at 150°-200°C and 2000-3000 psi of 1/1 H2/CO. 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

By polymerizing the trans isomer of 1,3-pentadiene two different types of crystalline cis-1,4 polymers have been obtained, one with an isotactic, the other with a syndiotactic structure. The isotactic polymer was obtained by homogeneous systems from an aluminum alkyl chloride and a cobalt compound, the syndiotactic one by homogeneous systems from an aluminum trialkyl and a titanium alkoxide. Some features of the polymerization by Ti and Co catalysts are examined. IR and x-ray spectra, and some physical properties of the crystalline cis-1,4 polymers are presented. The mode of coordination of the monomer to the catalyst, and possible mechanisms for the stereospecific polymerization of pentadiene to cis-1,4 stereoisomers are discussed. 

Attempts to isolate the complex which forms trans polymer have been made, but no pure compounds have yet been isolated. From cobalt chloride, solid or liquid products were obtained which have variable composition. (Co = 5.7-15%, A1 = 5.2-10.6%, Cl = 20.6-26.2%, N = 4.5%, and replaceable ethyl groups 1.2-16.9%). It seems probable that in certain of these products some of the amine cobalt chloride complex is present without coordinated AlEt2Cl. The corresponding products from cobalt octoate have all undergone decomposition to a greater or lesser extent during isolation, but by suitably protecting the catalyst with other donors such as ethers or nonpolymerizable dienes, it may be possible to isolate a stable product. 

In addition to the binary catalysts from transition metal compounds and metal alkyls there 2ire an increasing number which are clearly of the same general type but which have very different structures. Several of these are crystalline in character, and have been subjected to an activation process which gives rise to lattice defects and catalytic activity. Thus, nickel and cobalt chlorides, which untreated are not catalysts, lose chlorine on irradiation and become active for the polymerization of butadiene to high cis 1,4-polymer [59]. Titanium dichloride, likewise not a catalyst, is transformed into an active catalyst (the activity of which is proportional to the Ti content) for the polymerization of ethylene [60]. In these the active sites evidently react with monomer to form organo-transition metal compounds which coordinate further monomer and initiate polymerization. 

This monomer is usually obtained as a mixture of the cis and trans isomers both of which have been polymerized with coordination type catalysts. Polymerization of the cis form is considered to be preceded by isomerization, since those catalysts which do not isomerize the cis monomer (e.g. cobalt salt—organo aluminium halide) selectively polymerize the trans isomer. A kinetic study of the polymerization of cis 1,3-pentadiene using Ti(OBu-n)4/AlEt3 (Al/Ti = 1.3—6) as catalyst has been published [267]. This gives a polymer containing ca. 73% cis 1,4 15—16% trans 1,4 and 11—12% 3,4 microstructure. 

Medium-c/5 lithium-polybutadiene was first developed by Firestone Tire and Rubber Company in 1955 [86]. Solution polymerization using anionic catalysts is usually based on butyllithium. Alkyllithium initiation does not have the high stereospecificity of the coordination catalysts based on titanium, cobalt, nickel, or neodymium compounds. Polymerization in aliphatic hydrocarbon solvents such as hexane or cyclohexane yields a polymer of about 40 % cis, 50 % trans structure with 10 % 1,2-addition. However, there is no need for higher cis content because a completely amorphous structure is desired for mbber applications the glass transition temperature is determined by the vinyl content. The vinyl content of the polybutadiene can be increased up to 90 % by addition of small amounts of polar substances such as ethers. 

Coordinate Homopolymerization. When Ziegler-Natta catalysts of the type TiCl4/alkylaluminum compounds are used, no polymerization occurred because the cyanoprene (like acrylonitrile for instance) reacts with the catalyst and destroys it. Polymerization occurs, however, when metal acetyl acetonates and organoaluminum compounds are used. For example, coordinate polymerization with a mixture of cobalt acetyl acetonate and ethylaluminum dichloride results in a polymer that corresponds mainly to the radical-produced polymer. 

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