The First Organometallic Compounds WILLIAM CHRISTOPHER ZEISE AND HIS PLATINUM COMPLEXES By L. B. Hunt The Johnson Matthey Group The great interest being taken in the organometallic compounds 0.f thr platinum metals is evident in the current literature, in the .first Inter- national Conference on the Chemistry of the Platinum Group Metals held in Bristol in 1981, and now by the second conference to take placp in Edinburgh in July. This article reviews the preparation o,f the .first such compounds over a hundred and ,ffty years ago and thr acrimonious debate that ensued over their true constitution, continuing with a brief account of the early development o,f a ,further rangr o,f platinum complexes that have come to play an important part in industrial chemistry. During the last thirty years there has the son of the local pharmacist. After leaving developed a concentration of interest upon the school Zeise was himself apprenticed for a time preparation, structure and properties of a wide to Gottfried Becker, Royal Court pharmacist in range of organometallic compounds of the Copenhagen who combined this activity with platinum group of metals, much of this directed lecturing on chemistry at the university there, towards their usefulness in the catalytic syn- but poor health shortly caused him to return to thesis of a number of commercially valuable the family business in Slagelse. Here he con- chemical products. The most familiar industrial tinued to study chemistry and to absorb the examples of this type of reaction include, of new concepts put forward by Lavoisier, while in course, the carbonylation of methanol to acetic 1806 he was able to return to Copenhagen acid, the conversion of ethylene to acetaldehyde where he was taken into the family of Hans and the hydroformylation of olefins to Christian Oersted (1777-185 I) who had aldehydes, while other such large scale applica- recently been appointed extraordinary professor tions will undoubtedly be developed in the near of physics and chemistry in the university. Both future based upon the versatility of these com- men were the sons of pharmacists who were plexes as homogeneous catalysts where they well known to each other and Oersted invited offer high activity per unit weight of metal, Zeise to become his lecture assistant, a position high selectivity and long life. from which he was able to continue studying The original discovery of the first such chemistry and pharmacy, graduating in I 8 I 5 compound-and in fact of the first and going on to obtain his doctorate two years organometallic compound of any metal-took later with a thesis on the action of alkalies upon place, however, as long ago as 1830, at a time organic substances. The following two years he when organic chemistry was in its infancy, spent abroad, first under Professor Friedrich when but a relatively few organic compounds Stromeyer at the University of Gottingen and were known, and when their constitution was then in Paris where he was delighted to become barely if at all understood and the subject of acquainted with Berzelius, a friend of Oersted’s great argument. who was then spending almost a year there. The The credit for this discovery goes to William great impression made upon the young man- Christopher Zeise, born in Slagelse in Denmark Zeise was ten years junior to Berzelius-was to Platinum Metals Rev., 1984, 28, (2), 76-83 76 \K illiam Christopher Xeisr I 789- I847 I<eginninghis career as a pharmacist, Zeisc- hccatne first an assistant to llans (Ihristian Oersted in the 1niversit! of (.optmhagen and thcw. after a period in Giittingen and Paris. returned as Profvssor or ( hemistr) there. Ilc prepared the first organometallic compound of platinum-or of any mc-tal-in 1830. This involved him in considc.r- ahlc- controvwsy with Liehig hut hc. wits proved to hc. rorrrct in his interprctation. llr also discovvred thv xanthi1tc.s and the merc.aptans and in grneral hrlpi to lay thr foundations of organic rhemistry in thr first half of the nirwteenth rrnlitr! 1 rom purrrail palmed b\ F Hdrtrd h! wurtc\\ <it the Natmnal Htrrortc Mu~eum01 1)cnmark influence him for the remainder of his career first in Latin and then in English, French, and the two remained on friendly terms for the German and Italian describing his classic rest of their lives. Zeise also met and talked experiment on 21 July 1820 on the discovery with the older French chemists Berthollet and of electromagnetism. Repeating his earlier Laplace, attended several meetings of the experiments now with a more powerful battery, AcadCmie des Sciences as well as Vauquelin’s Oersted wished to have present six trusted lectures at the College de France. Among the scientific colleagues as witnesses, and these younger men he enjoyed the friendship of included “that very skilful chemist Mr. Zeise, Chevreul and Thenard. Doctor of Philosophy”, so securing him a Returning home at the end of 1819, Zeise certain publicity throughout Europe (2). was asked by Oersted to direct his laboratory Zeise’s first incursion into the chemistry of experiments and in fact he established one of platinum dates from 1827 when he reported to the first laboratories in Europe for analytical the Royal Danish Academy of Sciences the pre- and organic chemistry. Two years later he was paration by the action of alcohol upon platinous appointed extraordinary professor of chemistry chloride of a compound of platinum, oxygen at the University of Copenhagen and then, and carbon that had the properties of igniting from 1829 until his early death in 1847, he not only oxygen and hydrogen but that also served also as professor of organic chemistry at became red hot in alcohol vapour just as did the Royal Polytechnic Institute of Copenhagen the compound discovered by E. Davy, thereby that had been established on the initiative of liberating acetic acid. This he named Oersted, who became its first director (I). “chloridum platinae inflammabile” (3). Oersted’s high opinion of Zeise is clearly Edmund Davy (1785-1857), the younger shown in the famous paper that he published cousin of Sir Humphry, had published in I 820 Platinum Metals Rev., 1984, 28, (2) 77 an account of his preparation of very finely immediately following his main publication divided platinum by reducing a solution of (to). In the manner of the time, when many platinum sulphate with alcohol and of its great newly prepared compounds were given the activity at room temperature in the oxidation of name of their discoverer, the potassium com- a further quantity of alcohol (4). This swiftly pound became known, and is still known to this encouraged Johann Wolfgang Dobereiner day, as Zeise’s Salt, a compound we should now (I 700-1 849) to repeat the experiment, yielding identify as K[PtC13(C2H4)].H20. what we should now refer to as platinum black, Zeise called the salt “sal kalico-platinicus but unlike Davy he realised the great sig- inflammabilis” in his original Latin paper, and nificance of the discovery, thus helping to “entzundliches Kali-Platin-Salz” in the German initiate the study of heterogeneous catalysis (5). version. At this time the adoption of Dalton’s Zeise’s paper was published in German in Atomic Theory together with the methods of I 827 (6) and also referred to by Berzelius in his organic analysis developed by Gay Lussac, Jahresbericht for 1828 (7) while a year later Berzelius and Liebig made it possible, although Liebig reviewed the work of all three, maintain- rather lengthy and tedious, to determine ing that empirical formulae although of course it was ‘‘this black powder of Messrs. Davy, Zeise and many years before either strUCtUra1 fOlTlUlat?Or Dobereiner is nothing else than extremely finely a reasonable system of nomenclature became divided metallic platinum” (8). possible. Zeise believed his salt to be a deriva- tive of ethylene and he wrote: The Classic Paper “In this compound a portion of the chlorine is It was in I 830 that Zeise presented a paper in present in the same manner as in metal chlorides, Latin to the Universitv of CoDenhagen. but another portion in the manner as in published under the title C h 1or at her (et h y 1e n e c h 1 or i de ) and Chlorwasserstoffather (ethyl~I chloride) . “De chlorido platinae et alcohole vini sese Accordingly it is very probable that the invicem permutantibus nec non de novis sub- flammable chloride is a compound of platinum stantiis inde oriundis.” chloride and chlorinated hvdrocarbon.” (The reaction between platinum chloride and He therefore set about a painstaking wine alcohol and on the new substances arising therefrom.) series of analyses This paper, contained in the Anniversary “which I have performed with great care; for the precise knowledge of the components of this sub- Volume of the University for 1830, was quickly stance seemed to me very desirable, not only published in Poggendorff s Annalen der Physik because this compound offers a combination of und Chemie and in Schweigger’s Journal fur elements that seldom occurs, but also because a Physik und Chemie (9). correct determination of the proportions between carbon, hydrogen and chlorine might perhaps In his introduction Zeise referred to his throw some light on the nature of chlorather and earlier work as opening the way to his present other compounds of this type”. research, adding that administrative work and The paper then continues with a long and other studies had delayed his pursuing the detailed account of his analytical methods, subject . using the atomic weights adopted by Berzelius Using now platinic chloride instead of in 1826 in which oxygen was taken as 100, and platinous chloride-although some platinous concluding with three alternative formulae: compound remained in the mixture-dissolving “2 PtCI’ + 4H‘C + KCI’ this in alcohol, evaporating excess solvent and or 2 PtCl + 2(2H’C + CI) + KC12 reacting the residue with potassium chloride, or, if desired Zeise obtained “very beautiful yellow crystals”, 2(PtCI + 2H‘C + C1) + KCI’”.