September 2008 SCALACS: Dr. Herb Kaesz

Silver Circle Reminiscences
The Synthesis of Ditechnetium Decacarbonyl
By Dr. Herb Kaesz

I started my career at UCLA in August 1960 and in this reminiscence I would like to describe how my co-workers and I came to synthesize one of the last carbonyl complexes to be discovered. Shortly after my arrival at UCLA I was approached by Jack Hileman, a colleague on sabbatical leave from El Camino College, Torrance CA. Jack wanted to carry out the synthesis of various transition metal carbonyls in which he had an abiding interest and which could serve as intermediates in our group’s research in organometallic chemistry. During the academic year 1960-61, Jack was successfully preparing a selection of known metal carbonyl complexes such as M(CO)6, M = Cr, Mo, or W. Here is a photo of Jack Hileman at UCLA in 1961.Photobucket

While the above was taking place, the Atomic Energy Commission in Washington DC had initiated a program to facilitate investigations of the radioactive elements that were isolated in the reprocessing of nuclear reactor residues (Atoms for Peace Program). An announcement appeared in Chemistry & Engineering News (C&EN, Feb 27, 1961, p. 52), offering weighable quantities of ammonium pertechnetate at a reasonable price, namely $100/g, from the Oak Ridge National Laboratories. This was a remarkable drop from the earlier cost of $2,800/gram. The carbonyl complex of technetium , placed in the periodic table between those of manganese and rhenium, had not as yet been attempted. We thus purchased a gram of NH4TcO4 and converted it into Tc2O7 by heating at elevated temperature under a stream of elemental oxygen. The heptoxide was next transferred to a copper-lined autoclave and converted into Tc2(CO)10 under CO pressure. No solvent was needed: the CO gas served both as the reducing agent as it was converted to CO2, as well as the ligand in forming the carbonyl complex. Technetium-99 is a weak beta emitter, whose radioactivity is safely contained by the walls of normal pyrex laboratory ware. Direct contamination however was still a danger because of the general toxicity of the metal carbonyl complexes.

In recognition of the pioneering work on dirhenium decacarbonyl, we sent Prof. W. Hieber at the ETH in Munich, Germany, a preprint at the same time that we submitted our communication also co-authored by D. K. Huggins to the Journal of the American Chemical Society (appearing in vol. 83 (1961) p. 2953 ). Prof. Hieber was also working on the synthesis of Tc2(CO)10 with C. Herget, but only in trace amounts, and eventually reported his results in Angew. Chemie (vol. 73 (1961) p. 579) citing our earlier report.

From this exchange of professional courtesies Prof. Hieber was prompted to recommend to his students as well as to those of Prof. E.O. Fischer to come to UCLA for postdoctoral studies. In this group were Drs. G. Buerger, B. Deubzer, W. Fellmann, H. Brunner, A. Maasboel, C.G. Kreiter and R. Aumann. The latter three were co-sponsored by my eminent colleague at UCLA, the late S. Winstein. The outstanding work of the above-named collaborators undoubtedly helped me to achieve tenure at UCLA.