Günther Wilke (1925–2016) (2017)

Günther Wilke, Director of the Max Planck Institute (MPI) for Coal Research from 1969 to 1993 passed away on December 9, 2016 at the age of 91. He profoundly influenced the field of organometallic chemistry and catalysis research, in particular homogeneous transition-metal catalysis. His findings have become fundamental elements of contemporary science, and many former co-workers whom he influenced and supported have held, or currently hold key positions in both academia and in industry. Günther Wilke was born in Heidelberg, son of the physical chemist Professor Ernst Wilke. His youth was marked by the early loss of his father and the turmoil of war. In the winter semester 1945–1946, he began his chemistry studies, first in Karlsruhe and subsequently in Heidelberg, where he completed his doctorate in 1951 under the supervision of Professor Freudenberg on “Investigations on the Formaldehyde-Liberating Group in Lignin and in Model Compounds” (Untersuchungen über die Formaldehyd abspaltende Gruppe im Lignin und in Modellsubstanzen). His enthusiasm for research and the role model provided by his supervisor stimulated his love of organic chemistry, which later proved to be highly valuable in his research on organometallic chemistry. On Freudenberg's recommendation, Wilke then moved to Mülheim as a scientific assistant to Karl Ziegler, and built up his own research group there. Wilke's scientific breakthrough came in 1955 when he discovered the cyclotrimerization of butadiene to form cyclododeca-1,5,9-triene in the presence of titanium- and nickel-containing Ziegler catalysts. Further work led to a collection of cyclic molecules of varying ring sizes through the combination of two, three, and four butadiene molecules and through co-oligomerization with other unsaturated compounds. At the time, such unsaturated ring compounds were regarded almost as exotic species due to their difficult synthesis. However, he showed that these could be produced in high yields by using specific arrangements in the coordination spheres around the metal centre. Many of these cyclic olefins found industrial applications and are produced on scales of several thousand tons per year. Cyclododecatriene was used in the production of special types of nylon (such as Vestamid and Qiana). Cyclooctadiene is a precursor for Vestenamer that is used as a plasticizer in the rubber industry. Scientific discoveries have always been used for technological innovations. On the other hand, technological discoveries have always motivated scientists to research the related scientific problems. In his attempt to rationalize the mechanism of nickel-catalyzed oligomerization, Wilke entered unexplored scientific territory and shaped the field of homogeneous transition-metal catalysis (for an overview, see Angew. Chem. Int. Ed. Engl. 1988, 27, 185–206). New compound classes could be accessed on a preparative scale, including “naked nickel” complexes such as bis(1,5-cyclooctadiene)nickel(0), cyclododecatrienenickel(0) and tris(ethylene)nickel(0). In addition to Ni(η3-C3H7)2 , homoleptic π-allyl complexes could be synthesized for almost every transition-metal group and their catalytic properties were studied. For example, in a reaction that was brought to technical maturity in Japan, Cr(η3-C3H7)3 could be used in the polymerization of ethylene to linear polyethylene without the need for further additives or activators. Wilke's detailed studies on the mechanism of the cyclooligomerization of butadiene were particularly noteworthy. By isolating intermediates that were often extremely unstable, and by using in situ spectroscopic methods, a complex interplay between π-olefin and π-allyl complexes was elucidated. His most important contribution to the advancement of homogeneous transition-metal catalysis was the insight that the molecular processes were determined by the relative arrangement of the substrates in the coordination sphere of the metal centers, and that this arrangement could be tuned through the choice of the transition metal and the use of coligands. Whilst the reaction of bis(π-allyl)palladium with butadiene results in linear n-dodecatetraene, the use of tris(π-allyl)cobalt results in high yields of methylheptatriene. However, the application of bis(π-allyl)nickel results in the product of a cyclotrimerization, namely cyclododecatriene; and when PR3 ligands are added, the trimerization becomes a dimerization to form cyclooctadiene. In this way, a new research field was opened up that quite impressively showed how variation of steric and electronic properties of the co-ligands can influence reactions. This discovery was demonstrated virtuoso in countless reactions in Mülheim. An impressive example of this principle of ligand control was the nickel-catalyzed dimerization of propene, which, according to the choice of PR3 ligands, afforded either linear or branched C6 olefins. The use of chiral phosphine ligands was studied early on in Mülheim, and remarkably high ee values were reached for the codimerization of ethylene with other olefinic substrates (hydrovinylation), which are to some extent still the benchmark for these reactions today. This research represented a major contribution in establishing organometallic catalysis as in independent research area, and the MPI in Mülheim become a leading center for homogeneous catalysis. A large number of both German and foreign students spread the knowledge and the sophisticated scientific methods worldwide. Wilke's work was also used in industry, and his contributions can be clearly recognized in several industrial processes from the oligomerization of butadiene to hydroformylation, hydrocyanation, and the oligomerization of ethylene. The success of the institute was not least due to the sensitive way that Wilke interpreted his role. He allowed group leaders a great deal of freedom to carry out their research (see, for example, the special issue in memory of Karl Ziegler: Angew. Chem. Int. Ed. Engl. 1973, 12, Issue 12). Many fruitful interactions with the scientific service departments often resulted in new methodological developments. Under the aegis of Wilke, a great deal of notable research outside classical organometallic chemistry was carried out at the institute. Two striking examples are extraction with supercritical fluids (“destraction”, such as the industrial decaffeination of coffee (K. Zosel)) and metal-based materials for hydrogen storage (B. Bogdanović). Wilke's scientific achievements were recognized early on by the Max-Planck-Gesellschaft (Max Planck Society), and he was made a scientific member in 1963. In 1967, he was appointed Second Director at the MPI for Coal Research, and in 1969, he succeeded Ziegler as head of the institute. Beyond the institute, he was a member of the Senate of the Max Planck Society from 1973–1976 (Chemical-Physical-Technical Section) and was Vice-President from 1978–1990. He had a keen personal interest in the rapid creation of a Max Planck research landscape in the “new countries” after German reunification in 1989. The MPI for Coal Research supported two Max Planck research groups in Rostock on organometallic and asymmetric catalysis as well as one in Jena on CO2 chemistry. One of the authors of this Obituary is grateful that this environment allowed him to complete his Habilitation. Cross-linking the Max Planck Society with university research and teaching was a key priority for Wilke. As Dean of the Chemistry Department at the newly founded University of Bochum Ruhr-Universität Bochum, he made an enormous contribution to its successful development. He was awarded honorary doctorates by seven German and foreign universities. He was President of the Gesellschaft Deutscher Chemiker (GDCh; German Chemical Society), who also made him an honorary member. His pioneering research and his incredible personal enthusiasm for scientific and technical advances were reflected in his election to national and international academies as well as to the boards of large companies, and were recognized with numerous honors and awards. Although he was rightly proud of all of these, only a few can be mentioned here: Commander's Cross (1978) and Knight Commander's Cross (2000) of the Order of Merit of the Federal Republic of Germany, Emil Fischer Medal, Karl Ziegler Prize, Austrian Cross of Honour for Science and Art, Centennial Foreign Fellow (American Chemical Society), Sir Edward Frankland Prize (Royal Society of Chemistry) and honorary member of the American Academy of Arts and Sciences. Our alma mater, the RWTH Aachen, is very proud that in 1962, Günther Wilke completed his Habilitation here with the thesis “Synthesis of Reactions of Cyclododecatrienes-(1,5,9)” (Synthese und Reaktionen von Cyclododecatrienen-(1,5,9)). Many students who completed their diploma or doctoral studies under his supervision received their degree or doctorate from the RWTH Aachen, including one of the grateful authors of this Obituary. In 1976, the RWTH recognized this fruitful cooperation with the award of an honorary doctorate to Wilke. We consider it an honorable privilege that we were invited to write this tribute to Günther Wilke. Both of us have a lot to thank him for personally. We mourn the loss of our academic teacher and mentor. The field of chemistry has lost an outstanding scientist and a great personality.