Geoffrey Wilkinson and Platinum Metals Chemistry By M. L. H. Green University of Oxford, England and W. P. Griffith Imperial College of Science, Technology and Mrtlic.inr. London

At this time, the second anniversar?,of Geoffrey WZkinson’s death on 26th September 1996, his work and influence on the development ojinorganic chemistry and the chemistry of the platinum group metals are recalled by two of his former students and colleagues. Geoffrey Wilkinson’.s early life and career, important areas of his platinurn metals research and work leading to the award in 1973 of the Nobel Prize are surveyed. He is remembered by his relationship with Johnson Matthex his work at Imperial College and by affectionute anecdotes,from the laboratory

Professor Sir Geoffrey Wilkinson, F.R.S. (or of his ex-students came to work for it. On his Geoff as he was always called by his students twice-yearly visits to the Technology Centre in and colleagues) was one of the greatest inter- Sonning Common he would always take a plas- national post-war inorganic chemists; he made tic shopping bag filled with platinum metals remarkably original contributions to many areas residues, garnered from his research group and of transition metal chemistry, especially homo- from his colleagues - the used materials from geneous catalysis, organometallic and co-ordi- the loan scheme. nation chemistry. His research career, spanning On his retirement in 1988 to become Professor some 54 years, involved well over half of the ele- Emeritus, Johnson Matthey expressed their ments of the Periodic Table - he worked with appreciation of this mutually productive rela- almost every d-block transition metal, most of tionship by providing Geoff with the spacious the lanthanides and some of the actinides and Johnson Matthey laboratory at Imperial College. main group elements. Much of his work con- Here he continued very productive work with a cerned the six platinum group metals, and indeed small, creative team to the day before his death. many of his most important discoveries involved In 1964 Geoffrey Wilkinson wrote an article them. Ofhis 557 publications (l), well over one for Platinum Metals Review on platinum group third are concerned with the platinum metals. organometallic n-aromatic complexes (2). This article, however, preceded his important dis- The Johnson Matthey Connection coveries in the catalytic chemistry of these ele- The platinum metals Geoff used were invari- ments. As a fuller account of Geoff’s chemistry ably supplied by Johnson Matthey through the has already been published (l), this report will loan scheme (inaugurated in 1955 by his great focus on his life and work with the platinum friend, the late Frank Lever). This scheme has metals in the order of their interest to him, list- done much to foster university research in plat- ing items published in Platinum Metals Review. inum metals chemistry in the U.K. and over- seas. Over the years Geoff developed a close Early Life and Education connection with Johnson Matthey: not only were Geoffrey’s grandfather (also Geoffrey there the patents (involving for the most part Wilkinson) came to Todmorden, a small ‘cot- his rhodium catalysts) and consultancy, but also ton town’ in the West Riding of Yorkshire, close he had many kiends in the company - and some to Lancashire, from the Yorkshire town of

Platinum Metals Rev., 1998, 42, (4), 168-173 168 Professor Sir Geoffrey Wilkinson 1921-1996 A Yorkshireman by birth, Geoffrey Wilkinson started his working life, during World War 11, on the atomic bomb project in Canada and then the United States. He returned to England in 1956 to the Sir Edward Frankland Chair of Inorganic Chemistry, at Imperial College in London. He was awarded the Nobel Prize for Chemistry in 1973

Boroughbridge. Geoffrey’s father, Harry, better taught. Geoff won a County Scholarship married Ruth Crowther, a weaver, and Geoffrey in 193 1 to Todmorden Secondary School (later was born on 14th July, 1921, the first of three Todmorden High School). A remarkable num- children, in the village of Springside on the ber of its pupils later became famous, including outskirts of Todmorden. Sir John Cockcroft, who worked with Rutherford In 1926 the family moved into Todmorden, at Cambridge and was to become, in 195 1, the which lies at the junction of three deep valleys first of the school’s two Nobel Laureates. Geoff in the heart of the Pennines, where the sur- made exceptional progress and in 1939 won a rounding moors rise 1000 feet above the town. Royal Scholarship to the Imperial College of The present population of 13,000 is about half Science and Technology, London University. that before the decline of the cotton industry, At Imperial his main subject was chemistry but there is still a strong local pride and sense but he also studied geology as an ancillary of community which Geoff shared all his life. subject, indeed in those early days he almost His eyes would light up when he spoke of “Tod” gave up chemistry in favour of geology. He or of the superb countryside close by. He often graduated in 1941 with a first class honours returned to the town to see friends and family, B.Sc. degree, the top student of his year, and and enjoyed walking and climbing in the area, went on to do a Ph.D. under H. V. A. Briscoe in the Lake District and the Yorkshire Dales. (at that time the only Professor of Inorganic Geoff‘s interest in chemistry began early. At Chemistry in the country) on “Some Physico- the age of six he was fascinated to see his father chemical Observations on Hydrolysis in the - a house painter and decorator - mixing his Homogeneous Vapour Phase”. This rather materials. His uncle managed a factory making Delphic title conceals the fact that the main sub- Epsom and Glauber’s salts in Todmorden, and strate studied was phosgene (Geoff later Geoff would recall how he loved to go on remarked that Briscoe “directed his Ph.D. Saturday mornings to tinker in the small labo- research from a safe distance”). ratory at the factory. Indeed, the family hoped In 1942 he was selected by the Joint Recruiting that he would eventually become its manager. Board as a scientific officer at the Atomic Energy His parents, like most people at that time, had project in Canada, and sailed to Halifax, Nova left full-time education by the age of 12 and they Scotia in January 1943. In Canada he worked were determined that their children should be at the University of Montreal and then at Chalk

Platinum Metals Rev., 1998, 42, (4) 169 River, Ontario, on nuclear fission with many this day. Twenty years later Geoff wrote a vivid celebrated scientists -John Cockcroft (from his personal account of the discovery (4). From old school), Bertrand Goldschmidt, Charles 1952 to 1953 he made a number of other Coryell, Alfred Maddocks (later to go to bis(cyclopentadieny1) complexes, including those Cambridge), Jules Gueron and Pierre Auger of ruthenium, rhodium and iridium. During this being amongst them, and two scientists later period he used the fledgling technique of nuclear convicted of being spies for the Soviet Union, magnetic resonance (NMR) to show that cova- Alan Nunn May and Bruno Pontecorvo. lent metal hydrides (in this case Cp2ReH)gave After the war Geoff returned briefly to Britain high-field ‘H NMR shifts. This was crucial to and then went to the Lawrence Livermore his later work on rhodium hydrido complexes Laboratory at the University of California, and their catalytic properties. Berkeley, to work with Glenn T. Seaborg on the production of neutron-deficient isotopes of the Return to Imperial College transition elements and the lanthanides. It was In 1955 Geoff was appointed to Briscoe’s old

said by Seaborg (and Geom that he made more chair at Imperial College ~ still the only estab- artificial isotopes - eighty nine - than anyone lished chair of inorganic chemistry in Britain - has ever made. From this time he started to and arrived there in January 1956. At 34 he was amass his vast knowledge of descriptive inor- one of the youngest professors that the College ganic chemistry, since in those days it was essen- has ever had, and here he did most of his plat- tial for nuclear chemists to have a profound inum metals work. It is tempting to trace this knowledge of the chemistry of the transition profound interest in platinum metals chemistry metals, the lanthanides and the actinides in order to his wartime and early peacetime radiochem- to devise appropriate means of separating and ical work, when he had made new radioisotopes identifying the products of nuclear fission reac- of rhodium and ruthenium. However, it is much tions. One of his nuclear transmutations was more likely that his fascination with these met- that of platinum into gold, which caught the als derived from his early experience and knowl- public imagination after a report in 1948 in the edge of their general chemistry, and in partic- ‘San Francisco Chronicle’ (“Scientist discovers ular with the remarkable versatility of oxidation gold mine in the cyclotron”). state changes exhibited by the metals, later In 1950 he went to M.I.T. and turned to co- harnessed for his catalytic work. ordination chemistry research. His first paper on this concerned the isolation of the unusual Rhodium Chemistry zerovalent complex, [Ni(PCl,),] (3). In 1951 he Geoff once said that much of his chemistry was appointed Assistant Professor of Chemistry concerned the ‘three Rs’ - rhodium, ruthenium at Harvard, and it was here that he did the and rhenium. At Berkeley, as part of his radio- research on ferrocene and other cyclopentadi- chemical work, he isolated the short-lived ‘%h, enyl compounds which was to lay the corner- one of the many fission products of ‘W, and stone of his Nobel Prize. In 1976, after this in 1953 he made salts of the [CpzRh]’ cation. award in 1973, he received his knighthood. Then in 1961, in work that he himself carried out, he reacted cis- and tr~ns-[RhCl~(en)~]’with The Structure of Ferrocene and sodium borohydride in aqueous solution to give Early Platinum Metals Work [RhHCl(en)’]’ (detected by the high-field shift In 1951, the joint recognition by Wilkinson of the hydridic proton by ‘H NMR) (5). It was and R. B. Woodward of the unique “sandwich” on this occasion that he rushed into the labo- structure of ferrocene (bis(cyclopentadienyl)iron, ratory, demanded a Bunsen burner and a test Cp,Fe) was perhaps the most crucial point in tube, and returned later with the tube full of a his career; it launched the new wave of ‘organo- foaming brown liquid which he brandished transition metal chemistry’ which remains to about, calling “Who wants a Ph.D?” This early

Platinum Metals Rev., 1998, 42, (4) 170 work led to a paper on the isolation of was RhH(CO)(PPh,),. Nowadays most of the [RhH2(en),](BPh,), and the establishment of butyraldehyde used for synthesis of bis(2-ethyl- the reduction of quinone to quinol by hydride hexyl)phthalate, a plasticiser for PVC, uses transfer from [RhH(trien)Cl]+.In collaboration RhH(CO)(PPh,), as the catalyst. with that wizard of platinum metals chemistry, The early hydrogenation and hydroformyla- A. R. Powell of Johnson Matthey, salts of tion work was documented in a short article in [~UIH(NH,)~]’’and [RhH(H20)(NH,)4]”were this journal exactly thirty years ago, with fuller isolated; these materials were used to prepare papers in 1975 and 1988 (9). There is no doubt hydrido complexes of ethylenediamine and that this catalysis work, together with his work propylenediamine (6). in so many other areas, contributed to his Nobel prize of 1973, though the citation was for “sand- Hydrogenation and Hydroformylation wich” compounds. with Rhodium Complexes Geoff’s work on this topic has revolutionised Other Work with Rhodium our view of homogeneous catalysis effected by One of Geoff‘s major fascinations (foreshad- transition metal complexes and constitutes some owed in his only paper in this journal (2)) was of his most celebrated work. It is well reviewed with homoleptic alkyl and aryl complexes, mainly in articles by his graduate student, Fred Jardine, of the early transition metals. In 1968 he made who was the first to isolate the compound [Rh(CZHj)(NH,)5]”and, much later, in 1988 RhCI(PPh,),, universally known as Wilkinson’s and 1990, isolated salts of the remarkable methyl catalyst (7). complex [Rh(CH,),]’ and of the dimeric oxo- In 1965 Geoff reported that catalytically small bridged neopentyl complex R~&I-O)~[CH~C- amounts of reducing agents (such as hypophos- (CH,),],, respectively. Another achievement was phorous acid, zinc amalgam and dihydrogen the synthesis in 1991 of Rh(mesityl),, which has itself) would catalyse the otherwise slow sub- a pyramidal structure in the solid state. stitution reactions of rhodium(II1) complexes. He had earlier shown that RhCl,.nH,O would Ruthenium Chemistry absorb dihydrogen and convert hex-1 -ene Ruthenium he called “an element for the con- to hexane, and in 1965 he found that fac- noisseur’’. Again his first approach to this metal RhCI,(PPh,), would convert hex-1-ene to n- was via its radiochemistry in his early work in heptaldehyde, with dihydrogen and carbon Canada and the United States, followed by the monoxide under pressure at 55°C. However preparation of ruthenocene Cp,Ru and the RhCI,(PPh,), is difficult to make, and it was dur- ruthenicinium [Cp,Ru]+cation as a logical fol- ing an attempt to make some that RhCI(PPh,), low-up to his classic ferrocene paper. was produced. This compound was a much more In the 1960s he isolated a number of ruthe- effective catalyst for the hydrogenation of alkenes nium(I1) and (111) complexes of phosphines, and alkynes and also hydroformylated hex-l- arsines and stibines, including RuX,(LPh,), (X yne to n-heptaldehyde and 2-methylhexalde- = C1, Br; L = P, Sb) and RUX,(LR,)~(CH,OH) hyde. RhCl(PPh,), was made from the surpris- (L = P, As). These were precursors for many ingly simple reaction between RhCl,.nH,O in other complexes with a wide variety of ligands, ethanol with excess triphenylphosphine. It is such as dithiocarbamates, amines, nitriles and described in a classic paper of 1966 (8). carboxylates, and a number of them had use- Although RhCI(PPh,), is a hydrogenation cat- ful catalytic activities. Another highlight was the alyst (and subsequently chiral analogues were isolation of the first paramagnetic second-row developed by others for asymmetric synthesis, transition metal complexes, Ru2(OCOR),C1 (R for example for L-Dopa) Geoff later showed that = Me, Et, n-Pr). A variety of carboxylato com- it was not a hydroformylation catalyst, and that plexes of the form RuH(OCOCH,)(FPh,), were the compound responsible for the latter process found to be efficient hydrogenation catalysts for

Platinum Merals Rev., 1998, 42, (4) 171 The Nobel Prize for chemistry awarded to Sir Geoffrey Wilkinson in 1973 for his work on “sandwich” compounds

in 1982. His most celebrated work with osmium however lay with the aryl and imido com- plexes -he liked to refer to such highly unusual species as “text- book cases”. He made the alkyl complexes Os(VI)O(CH2SiMe,), and also the dimeric neo-pentyl OS*(vI)(O~CCHI)~(CH~S~M~J)+ In 1984 the tetrakis phenyl com- alk-1-enes. A review of this and other work on plex Os(IV)Ph, was isolated and in 1988, the ruthenium carboxylates has been described by tetrahedral complexes Os(IV) (2-CH3C,H,), and Steve Robinson, one of his former students ( 10). [Os(V)(2-CH,C6H,),]+were prepared. At that His later work with ruthenium was also very time, tetrahedral co-ordination was unprece- productive. In 1986 the novel aluminohydride dented for the tetra- or pentavalent oxidation complexes L,HRuAIH(p-H),AlH(p-H)2RuHLj states of second or third-row transition elements. (L = PMe,, PEtPh2, PPh,) were obtained from For imido chemists, the ‘Holy Grail’ was the RuClL and lithium aluminium hydride. In the isolation of a homoleptic complex containing mid-1 980s he isolated the alkyl complexes the =NR ligands, and in 1991 Geoff achieved RU~(IV)(~-O)~%(R = neopentyl, CH,SiMe,), this with the isolation and structural character- the tetrahedral homoleptic RuR., (R = o- isation, by electron diffraction, of the tetrahe- CH,C,H,, mesityl), salts of [Ru(CH,),]’-, and dral tertbutylimido complex Os(1V) (NBu),. some unusual ruthenium(n3 and (V) imido com- plexes. Alkyl complexes had become of increas- Iridium Chemistry ing interest to him; in fact, his Nobel Prize award Geoff did some work in the late 1960s on “irid- speech in 1973 was entitled “The long search ium iodate” (13), but he then seems to have for transition metal alkyls” (1 1) and in 1993 he neglected the metal until 1989 when he isolated wrote a review paper on the homoleptic alkyls salts of [Ir(CH,),]’-. and aryls of the platinum group metals ( 12). In 1991 he made the tetrahedral complexes Ir(IV)R.,, where R is a sterically hindered aryl, Osmium Chemistry such as 2-tolyl, 2,5-xylyl; and in 1992 he made Although he made ruthenocene and the Ir(mesityl),. In the same year he made ruthenicinium cation in 1952, soon after his fer- Ir(mesityl), which, like its rhodium analogue, rocene work, it was E. 0. Fischer (with whom has a pyramidal structure in the solid state. Also he shared the Nobel Prize) who first made in 1992 he isolated Ir(mesityl)2(SEt2)2,a very osmocene, Cp20s,in 1958. Geoff‘s first paper rare example of a planar iridium(I1) complex, at Imperial College concerned K[OsO,N], but by reaction of mer-IrC1,(SEt2),with the Grignard apart from this he came to osmium chemistry reagent Mg(rnesityl),(SEtJ2. relatively late in his research career. In the 1980s he made the acetato complexes: Palladium and Platinum Chemistry [Os(OCOCH3),(PMe~)llCl, OS~OCOCH,),C~@Y), Of the six platinum group metals, palladium and sky-blue K[OsO2(0COCH,),].2CH,COOH, and platinum received far less attention from the X-ray crystal structure of which was obtained Geoff than did the other four, perhaps because

Platinum Metals Rev., 1998, 42, (4) 172 these elements are less versatile in their oxida- which he would dismiss as ‘stamp collecting’. tion states and also, perhaps, because other well- Sometimes when a reaction seemed not to be known chemists in the country were doing much working he would offer the suggestion “Why palladium and platinum work. But, between don’t you goose it up” meaning, raise the tem- 1966 and 1970, he did show that the zerovalent perature. Geoff was not sympathetic to theo- complex Pt(PPh,), reacts with CS, to give retical chemistry and would often cite the story Pt(PPh3)z(CSz), while the reaction of of how the brilliant young Harvard theoretician Pt(PPh,)2(0,) with CO, CO, and CS2yielded Bill Mofitt had advised him that bis-benzene Pt(PPh,)2(C0,), Pt(PPh,),(C04) (a peroxocar- chromium would be unlikely to be stable. E. 0. bonate) and Pt(PPh,),(OZCS2), respectively. Fischer shortly afterwards reported this famous compound. Wilkinson the Man Geoff was always in a great hurry to publish For both of the authors of this article, Geoff new results and, from time to time, this led to was an academic supervisor in the late 1950s. errors; one example was the reaction product We wrote, in our joint obituary of him for ‘The between thiophene and iron pentacarbonyl Independent’: “The spirit in his research group which was published as thiopheneirontricar- was more like that of an urgent gold rush in bonyl. Gordon Stone later showed that there the West than the scholarly and disciplined calm was no sulfur present and the product was the expected in academia.” (14). If anything this unexpected butadieneiron tricarbonyl. Geoff understates the truth: he expected his students was not given to sulking over such matters but to work as hard as he did - seven days a week looked forward to the next new compound. or at least six, from early morning to late evening. Geoff was a doughty fighter for chemistry in He was, however, not a slave driver and was gen- the U.K., writing in blunt style to Prime erally tolerant of eccentric behaviour. When Ministers, ministers of education, vice chan- thwarted or stirred he made creative and inge- cellors and others charged with the care of fun- nious use of expletives - quite unsuitable for damental scientific research. He would refer quotation here - and he always had a ready sense to such powerful people in administration of fun. His enthusiasm was always infectious, dismissively as “the apparatchiks”. and he was an excellent raconteur and anec- Geoffrey Wilkinson was a remarkable scien- dotalist, with a remarkable memory. In those tist and an unforgettable person. His belief that days (the late 1950s) Geoff would often emerge innovative and creative synthesis is a powerful from his office in the late afternoon and wander tool for new chemistry is borne out by his vast up to each student in turn and say “Well, what’s range of scientific achievements. His legacy to new?”: his whole ethos being the search for some his former students and his enthusiastic influ- new aspect of chemistry. ence on chemistry have given us all many long- He was a severe critic of derivative chemistry term, far reaching benefits.

References 1 M. A. Bennett, A. A. Danopoulos, W. P. Griffith 7 F. Jardine,Rhodium Express, 1997,16,4;F. Jardine, and M. L. H. Green,J. Chem. SOC.Dalton Trans., Prog. Inorg. Chem., 1981, 28, 63 1997,3049 8 J. A. Osborn, F. H. Jardine, J. F. Young and G. 2 G.Willdnson, Platinum Metals Rev., 1964,8, (l), 16 Wil!&son,J. Chem. Soc. (A), 1966, 171 1 Platinum Metals Rev., J. 3 J. W. Irvine and G. Wilkinson, Science, 9 1968, 12, (4), 135; F. 195 1,113, Smith, op. cit., 1975,19, (3), 93; M. J. H.Russell, 742 op. cit., 1988, 32, (4), 179 4 G. Wilkinson, J. Organomet. Chem., 1975,100, 10 A. Dobson and S. D. Robinson, Platinum Metals 273 Rev., 1976, 20, (2), 56 5 G.Wilkinson, Proc. Chem. Soc., 1961, 72 11 G.Wilkinson, Nobel Foundation, 1974 6 K.Thomas, J. A. Osborn, A. R. Powell and G. 12 G. Wilkinson, Sci. Progress, 199314, 71, 15 Wilkinson,J. Chem. Soc. (A), 1968, 1801; A. R. 13 Platinum Metals Rev., 1969, 13, (4), 152 Powell, Platinurn Metals Rev., 1967, 11, (2), 58 14 “The Independent”, October 1, 1996

Platinum Metals Rev., 1998, 42, (4) 173