Dieter Sellmann (1941–2003): Coordination Chemistry of N2 Fixation

Abstract

Dieter Sellmann died unexpectedly on 6 May 2003, at the age of 62. He was an outstanding coordination chemist. His innovative contributions to the modeling of enzymatic nitrogen fixation, that is, the conversion of inert dinitrogen into ammonia under homogeneous catalysis and mild reaction conditions, have made him well known internationally, and have been an inspiration to many of his fellow scientists time and time again. Dieter was an exceptionally gifted synthetic chemist. Over a period of more than 30 years he synthesized interesting, unusual, and esthetically beautiful molecules, with an impressively large number of students.1 Dieter Sellmann entered the public scientific scene in 1972 at the Chemiedozententagung (German meeting of junior chemistry lecturers) in Heidelberg with a bang. Unforgettable for all of those present was the masterful, confident way in which he presented his first ground-breaking results in artificial N2 fixation: the dinuclear diimine complex trans-[(μ-N2H2){CpMn(CO)2}2]1 and its oxidized dinitrogen product [CpMn(CO)2N2].2 In 1989 followed the biomimetic complex [(μ-N2H2){Fe(“NHS4”)}2], which has many structural and electronic properties that are important in nitrogenase.3 The synthesis of this complex led him to formulate his much debated mechanism for catalytic N2 fixation in nature.4 The scientist Dieter Sellmann was strict—occasionally remorseless—toward others, but always toward himself as well, when it came to the question of “true” N2 fixation (under mild conditions). He did not accept elemental Li or Na to be mild reagents (not even in a disguised form). The reaction should occur under the same conditions as the natural process: in water, at 20 °C, under a pressure of 1 atm, and with a physiological redox potential. To realize his scientific dream, Dieter had to learn and develop a great deal of organic sulfur chemistry. After taking up an appointment at the University of Paderborn in 1976, he went on to design and synthesize novel sulfur-containing ligands, which are still used today by chemists around the world. Many of his compounds or ideas have been used willingly by others (also by this author) in their chemistry. Dieter was very generous. From 1980, then at the University of Erlangen, a large variety of thiolate and thioether ligands were synthesized, and their coordination chemistry and efficiency in N2 fixation was studied—with success: In 2001, N2 fixation under mild conditions at a Ru center was observed.5 Dieter was particularly motivated and excited over the last two years; he believed he was near his life's goal and that what he had dreamed of was really possible. He was an excellent teacher, who shared his enthusiasm for chemistry with his students in clear, concise, often elegant language. He was convinced that only difficult problems were worth working on and ambitious goals worth setting. He traveled a lot and lectured both in Germany and abroad, but relatively reluctantly. During a big conference he once observed, while he stood with a glass of cognac in his hand, as the sun set over the Pacific: “I would much rather be sitting next to my wife on the sofa in Erlangen right now.” And he really meant just that. Dieter was a stimulating speaker in discussions, both when he was asking and when he was replying to questions. He asked and answered questions in his inimitable manner: sometimes downright arrogant, but always precise. In this way he could explain the ins and outs of catalysis to a very renowned colleague in just a few minutes. Dieter was dedicated to the University of Erlangen and to his field, inorganic chemistry, to an exceptional degree. His rectors loved him, but sometimes also feared him, if he spoke out on matters of principle: for example, to assert that a chemistry laboratory course must have enough money and qualified staff, regardless of the current general financial situation. He fought with wit, carefully chosen words, and his sharp analytical mind against intellectual “nonsense” in committees and in science. One could have glorious arguments with him! Inorganic chemistry has lost a great scientist and an outstanding personality. We will miss his scientific ideas and his laughter.