Polymerizations catalyzed by noble metal‐olefin complexes

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Abstract
Several noble metal‐olefin complexes were prepared and studied as polymerization catalysts. Catalytic behavior of complexes toward specific monomers is invariably a property of the metal atom. Polymerization rates may depend upon ligands associated with the metal, but ligands do not alter the course of reaction. Olefin complexes of rho‐dium(I) chloride are superior catalysts for the emulsion polymerization of 1,3‐butadiene to crystalline trans‐1,4‐polybutadiene. The rates of polymerization are dependent to some extent upon the olefinic ligands. In all cases rates can be increased by addition of certain hydride donors. Chelating diolefins, such as 1,5‐cyclooctadiene and norbornadiene, can serve as stabilizing ligands in catalytically active complexes. When added as free diolefin to polymerizing recipes containing either salts or complexes of rhodium, however, chelating diolefins are effective inhibitors of polymerization. Olefin complexes of iridium(I) chloride do not polymerize butadiene, but are effective catalysts for the ring‐opening polymerization of norbornene in bulk, solution, or emulsion. Polymermerization rates are very sensitive to the nature of the ligands within the complex; the more unstable complexes give the faster rates. Specific hydride donors do not usually enhance catalytic activity of iridium complexes, and may lead instead to complete deactivation of the complexes. The selective behavior of complexes of various noble metals toward specific monomers is strikingly illustrated by polymerization of norbornadiene. Three different polymer structures are obtained from complexes of the three metals rhodium, iridium, and palladium. From rhodium polymer consists of nortricyclene units, from a 1,5‐addition. Iridium leads to ring‐opened oxygenated polymer, whereas palladium catalyzes formation of 1,2‐addition polymer.

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