8 Some Recent Developments in Coordination Chemistry
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J O H N C. B A I L A R , JR., H . I T A T A N I , M . J. CRESPI, and J. G E L D A R D Department of Chemistry and Chemical Engineering, The Noyes Laboratory, University of Illinois, Urbana, Ill.
This paper describes catalysts of the type (R Q) MX (R is an alkyl, aryl, or phenoxy group; Q is P, As, or Sb; M is Ni, Pd, or Pt; X is a halogen or halogenoid. Where M is Pd or Pt, a compound M'X or M ' X is added (M' = Si, Ge, Sn, or Pb (but preferably Sn, which forms the compound (R Q) M(SnX )X.) In the presence of such a substance, polyunsaturated compounds, especially esters of long chain fatty acids, are hydrogenated until one double bond remains. The hydrogenation is preceded by cis-trans rearrangement of the double bonds and migra tion of the double bonds along the carbon chain to form a conjugated system. Another research project has shown that certain bacteria can utilize the nitrogen from D-[Coen ]Cl but that L-[Coen ]Cl inhibits their growth. 3
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J t is common to liken a good deed or a wise word to a pebble dropped into the surface of a lake; it sets up a series of waves which travel out ward i n an ever-widening circle toward some distant and perhaps unknown shore. The analogy is a good one, not only because it is so apt, but also because it raises in each listener's mind a pleasant and sometimes nostalgic picture. We might properly apply this analogy to Werner's theory of the structure of coordination compounds, for certainly it has exerted an everwidening influence on all branches of chemistry, both pure and applied. It has taken over the major part of inorganic chemistry, has so modified our concepts of bonding that large areas of physical chemistry have been changed, has found a steadily increasing number of applications i n bio chemistry, has become the backbone of analytical chemistry, and has been more and more widely applied to many aspects of organic chemistry. N o r 103 In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.
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WERNER CENTENNIAL
can Werner's contribution be measured only in terms of ideas—tremendous as that contribution is. It must be measured also in terms of the training of his students, many of whom became distinguished chemists i n several fields of chemistry—Yuji Shibata and T. P . McCutcheon in inorganic chem istry, Paul Karrer and Paul Pfeiffer in organic chemistry, Arturo M i o l a t i in physical chemistry, E d m u n d Stiasny in leather chemistry, Charles H . Herty in industrial chemistry, and John Read, the chemical historian, to name only a few. Like other analogies, the likening of Werner's theory to the generation of waves when a pebble is dropped into quiet water is not perfect, for the ripples in the lake gradually fade away, whereas the coordination theory has steadily gained in importance and usefulness. The waves are be coming stronger and stronger. It is impossible to measure Alfred Werner's influence on chemistry, both because it is still growing, and because it is woven into the fabric of modern chemistry that one cannot separate it from the contributions of others. Suffice it to say, Werner was one of the few great geniuses of chemistry and certainly the greatest of modern times. A l l here today are his disciples, and each one of us owes him a great debt. As is well known, Werner was trained as an organic chemist and, at the time he applied himself to the problem of the structure of complex i n organic compounds, he had very little experience i n inorganic chemistry. His theory was not based on his own experimental work but entirely on the experiments of others. How much time he had spent in the study of inorganic complexes, we do not know, except that it was relatively little. His reading was extensive enough, however, to allow him to see a large number of relationships clearly and to synthesize them into the coordina tion theory which sprang fully grown from the mind of its creator. The experimental work came later. There were many chemists who found fault with the theory, and Werner had to devise and perform a host of experiments to substantiate his ideas. Fortunately, he was able, even tually, to establish the truth of the coordination theory beyond any doubt. It is but fitting that we should honor him in this centennial symposium. The number of papers which have been offered and the range of the topics which they cover tell, far better than I can, the impact which Werner has had. In this lecture, I should like to outline briefly two pieces of research i n coordination chemistry which have held our attention recently. The first of these involves a series of complexes which catalyze the isomerization and hydrogenation of poly-unsaturated systems in a quite specific way. The original goal of the research was to devise a method of hydrogenating the poly-unsaturated esters i n soybean oil without producing the fully saturated compounds. This work has been done under contract with the U . S. Department of Agriculture and authorized by the Research and Marketing Act. The
In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.
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BAILAR ET AL.
Coordination
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Catalysts
contract was supervised by the Northern Utilization Research and Develop ment Division of the Agricultural Research Service. The details of the experimental work, all of which has been done by Hiroshi Itatani, are being published elsewhere. The results of the work have been highly satisfac tory, not only from a practical point of view, but also i n opening several interesting fundamental questions to which we hope to find answers. The chief properties of these catalysts are: 1) They convert cis double bonds to trans double bonds. 2) They cause the double bonds to move along the hydrocarbon chain, probably i n a random fashion, until the double bonds become conjugated. 3) They bring about the reduction of all but one of the double bonds. If any further hydrogenation takes place, it is extremely slow and, i n most cases, can be disregarded. 4) Under properly selected conditions, reduction does not take place— only isomerization to the conjugated system. 5) When methanol or a mixture containing methanol is used as the solvent, hydrogenation takes place even i n the absence of elemental hy drogen. In that case, the hydrogen is furnished by the alcohol which is converted to aldehyde. Tetrahydrofuran can also furnish hydrogen, and there is some evidence that even benzene can play this role. Although the generality of these five properties has not been fully ex plored, the available evidence indicates that the reactions are not confined to the long chain esters but are applicable to a range of compounds. 6) I n the hydrogenation of the long chain esters i n alcohol solution, ester interchange is quite extensive. The catalysts which I wish to describe are of the type ( R Q ) M X , where R represents an alkyl or aryl group; Q, phosphorus, arsenic, or a n t i mony; M , nickel, palladium, or platinum; and X , a halogen or halogenoid. When M is palladium or platinum, an excess of a compound M / X or M ' X is added ( M ' = silicon, germanium, t i n , or lead). The catalyst which we have studied most extensively is a mixture of (
