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Nov. 5. 1962 RHODIUM SALTS AS BUTADIENE P O L Y M E R I Z A T I O N C a T A L Y S T S 4145 (iii) A portion of the reactants disappears to give material other than CbHg isomers a t a rate which is nearly independent of time. Evidently both cis and trans isomers participate in this reaction which presumably gives high boiling material.(iv) Beyond the maximum in the concentration of cis-pentadiene, the reaction ck-CHs= CHCH=CHCHa + hv d ~uLEs-CH~=CHCH=CHCHI (10) may account for the decrease in the cis isomer.These results give more direct evidence for the statement made in an earlier section that the general reaction2 is probably rapid when compared to the rates of rotation around the carbon-carbon bonds in the molecule. Reaction 8 may be pic-$2 V tured as proceeding through an excited state (V) which is probably the same as the state which leads to the cis isomer through rotation around the bond between C3 and C4. The latter operation has no energy barrier in the excited state up to an angle of r/214 and its rate may be comparable to the rate of rotation around the bond between CZ and Cp. Since the rate of reaction 8 is observed to be faster than reaction 9, it follows that the former is favored by a suitable configuration in the ground state in the molecules which undergo the process. l5Acknowledgment.-The author wishes to thank Dr. Harold L. Friedman for his advice and encouragement during the course of this work. He is grateful to Drs. J. Kumamoto and J. C. Powers for many helpful discussions.

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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.