Palladium-Catalyzed Alternating Copolymerization of Alkenes and Carbon Monoxide.

phinoethane) seemed mainly to stabilize intermediates, and often the catalytic reactions were slower when dppe was used instead of the most common monodentate triphenylphosphine. We will briefly review the history of “ligand effects” in catalysis before discussing a range of reactions for which a notable effect has been observed. It has taken quite some time before the positive effect that bidentates can have on selectivities and rates of catalytic reactions was fully recognized. Most of the established examples of bite angle effects involve diphosphine ligands. Therefore, many important catalysts containing a chelate ligand such as bipyridine and diimine will fall outside the scope of this review. The connecting bridge in these bidentates does play a dominant role in the performance of these catalysts, but systematic studies have not been published. The effects of phosphine ligands in catalysis have been known for quite some time. One of the first reports involves the use of triphenylphosphine in the “Reppe” chemistry, the reactions of alkynes, alcohols, and carbon monoxide.1 It was found that formation of acrylic esters was much more efficient using NiBr2(PPh3)2 than NiBr2 without ligand. In the commercial system, though, a phosphine-free catalyst is used. While the reaction was not yet understood mechanistically, the use of phosphines in catalysis attracted the attention of the petrochemical industry worldwide. An early example of a phosphine ligand modified catalytic process is the Shell process for alkene hydroformylation using a cobalt catalyst containing a trialkylphoshine.2 The reaction requires higher temperatures, but it leads to more linear product as compared to the unmodified catalyst. The general mechanism of the hydroformylation reaction has been known for a long time.3 Hydrocyanation as used by Du Pont is another early example of an industrially applied catalytic reaction employing ligands.4 It is a nickel-catalyzed reaction in which aryl phosphite ligands are used for the production of adiponitrile. The development of this process has played a key role in the introduction of the now very common study of “ligand effects” in the field of homogeneous catalysis by organometallic complexes.5 While several industries were working on new homogeneous catalysts, important contributions to the new field were made in academia in the early 1960s with the appearance of the first phosphinemodified hydrogenation catalysts. An early example of a phosphine-free ruthenium catalyst was published by Halpern.6 Triphenylphosphine-modified platinumtin catalysts for the hydrogenation of alkenes were reported by Cramer from Du Pont in 1963.7 In the same year Breslow (Hercules) included a few phosFigure 1. Bite angle: The ligand-metal-ligand angle of bidentate ligands. 2741 Chem. Rev. 2000, 100, 2741−2769

Ligand Bite Angle Effects in Metal-catalyzed C−C Bond Formation

Theoretical studies on reactions of transition-metal complexes.

The last 15 years of hydroformylation and carbonylation chemistry are reviewed, including technical and commercial aspects.

Progress in hydroformylation and carbonylation

The use of 13 carbon nuclear magnetic resonance (NMR) spectroscopy in the molecular characterization of macromolecules has advanced our knowledge into structural areas that have been nearly impossible to measure by other spectroscopic techniques. Innovative applications have led to determinations of polymer configurational distributions, comonomer sequence distributions, average sequence lengths, structure and distribution of short chain branches, and analyses of nonreactive end groups. As a result, the importance of 13C NMR to the field of polymer science cannot be overemphasized. The key to the success of 13C-NMR studies in defining polymer molecular structure has been a structural sensitivity which encompasses more than just a few functional groups or carbon atoms. A sensitivity to polymer repeat unit sequences of lengths from two to as many as five, seven, and even nine contiguous repeat units [1,2] has been observed. Of course, any structural technique that senses a unique response from as f...

A review of high resolution liquid 13carbon nuclear magnetic resonance characterizations of ethylene-based polymers

Efficient palladium catalysts for the copolymerization of carbon monoxide with olefins to produce perfectly alternating polyketones

13C Nuclear Magnetic Reasonance Spectroscopy of Polydienes, Microstructure of Polybutadiene

In the late 1940s, Reppe discovered a nickel catalyst for the co-oligomerization of ethene and carbon monoxide. Since then, various groups have made attempts to develop more efficient catalysts for this reaction. The recent discovery of a new class of very active palladium catalysts now allows, for the first time, ready access to a large variety of high-molecular-weight alkene/carbon-monoxide co- and terpolymers. The catalysts comprise a cis-coordinated palladium(II) species associated with weakly or non-coordinating anions. Their discovery has made it possible to develop a viable process for the commercial production of the first members of the new family of CARILON-olefin/carbon monoxide copolymers.



In this brief review, we highlight some key phenomena in polyketone catalysis. The elementary reaction steps in the palladium-catalyzed polyketone formation during chain propagation, initiation and termination are outlined. The role of bidentate ligands and the reasons for perfect alternation in polymer chain growth are dicussed. The attractive feature of the catalysts, that they also catalyze the co- and terpolymerization of olefins higher than ethene with carbon monoxide, is briefly noted. A parallel between polyketone catalysis by cationic palladium complexes and modern polyolefin catalysis by cationic metallocene complexes is suggested.

Alternating copolymerization of alkenes and carbon monoxide catalyzed by cationic palladium complexes

The Interaction of Color Centers and Cd+2 and Sb+3 Ions in Calcium Fluorophosphate

A class of highly efficient homogeneous palladium catalyst systems has been developed for the production of perfectly alternating copolymers of carbon monoxide with ethylene. Mixtures of carbon monoxide, ethylene and propene are converted to the corresponding alternating carbon monoxide/olefin terpolymers in which C3 units randomly replace ethylene units along the chain. The essential features of the catalyst systems described herein are that they are formed by the equimolar combination of a suitable bidentate phosphine ligand with a palladium(II) species in which the counter anions are weakly coordinating. For a series of diphenylphosphinoalkanes of general formula Ph2P(CH2)mPPh2 the most efficient catalyst system for production of high molecular-weight polyketones was found for m = 3. High rates with conversions of more than one million moles of carbon monoxide and ethylene per palladium centre were obtained. In methanol, the majority of the copolymer chains produced are polyketo esters of general formula H(CH2CH2CO)nOMe (I); analysis of methanol-soluble oligomer fractions show that diesters MeOCO(CH2CH2CO)nOMe (II) and diketones H(CH2CH2CO)nCH2CH3 (III) are also formed.

J. A. M. van Broekhoven

Papers

Efficient palladium catalysts for the copolymerization of carbon monoxide with olefins to produce perfectly alternating polyketones

13C Nuclear Magnetic Reasonance Spectroscopy of Polydienes, Microstructure of Polybutadiene

Alternating copolymerization of alkenes and carbon monoxide catalyzed by cationic palladium complexes

The Interaction of Color Centers and Cd+2 and Sb+3 Ions in Calcium Fluorophosphate

Palladium Catalysed Copolymerization of Carbon Monoxide with Olefins to Alternating Polyketones and Polyspiroketals