Author Profile
Helmut Werner
First published: 28 September 2010
Graphical Abstract
“My favorite subject at school was mathematics. My first experiment which I did together with a friend at the age of 11 was an oxyhydrogen gas explosion …︁” This and more about Helmut Werner can be found on page 8070.
References
- 1“Tricarbonylhexamethylborazolechromium”: R. Prinz, H. Werner, Angew. Chem. 1967, 79, 63;
10.1002/ange.19670790126 Google ScholarAngew. Chem. Int. Ed. Engl. 1967, 6, 91–92. Benzene C6H6 and borazine B3N3H6 are isoelectronic and isosteric molecules. This motivated Egon Wiberg in the 1930s to call borazine “inorganic benzene”. In association with kinetic studies to generate [(C6Me6)Cr(CO)3] from [Cr(CO)6] and after it had been shown between 1955 and 1960, mainly by the group of Fischer, that benzene and its derivatives were able to form not only sandwich complexes [M(C6R6)2] but also half-sandwich type compounds [(C6R6)M(CO)3], we became interested in trying to prepare an analogous compound with B3N3Me6 instead of C6Me6 as the ligand. Luckily, we didn’t know that several other groups had already attempted to achieve this goal but had failed. With [(CH3CN)3Cr(CO)3] as the starting material, Richard Prinz (my first PhD student) prepared [(B3N3Me6)Cr(CO)3] in 90% yield, which excited the borazine community and half a year later led to my position at Zurich.
- 2“The Synthesis of the First Double Sandwich Complex: The Dinickeltricyclopentadienyl Cation”: H. Werner, A. Salzer, Synth. React. Inorg. Metal-Org. Chem. 1972, 2, 239–248. Fischer had already had the idea to cover a sandwich (“burger”) with another structural level and to form a double sandwich (“double burger”) in the 1950s, and later it was strongly supported by the observation of the cations [Ni2(C5H5)3]+ and the Fe2 counterpart by mass spectrometry. In 1971, Albrecht Salzer succeeded at the synthesis of the nickel complex. In his PhD studies, he had investigated the reactivity of nickelocene towards nucleophilic and electrophilic reagents and, upon treatment of [Ni(C5H5)2] with trityl chloride, had obtained C5H5CPh3. Next, by using [CPh3]BF4 instead of [CPh3]Cl he isolated, besides C5H5CPh3, the BF4 salt of the double sandwich (subsequently called triple decker) [Ni2(C5H5)3]+ in nearly quantitative yield. One year later, the structure of the compound appeared on the cover of the abstract of papers of the VI. International Conference on Organometallic Chemistry and soon was included in the text books.
- 3“Electron-Rich Half-Sandwich Complexes—Metal Bases par excellence”: H. Werner, Angew. Chem. 1983, 95, 932–954; Angew. Chem. Int. Ed. Engl. 1983, 22, 927–949. Based on the work of Hieber in the 1930s, it was well known that metal carbonylates such as [Co(CO)4]- or [Fe(CO)4]2- readily react with electrophiles. The Vaska compounds trans-[IrCl(CO)(PR3)2], prepared in the 1960s, with a 16-electron configuration and a free pair of electrons at the metal, also proved to be Lewis bases. Before 1970, however, there were only a few hints that coordinatively saturated uncharged complexes with an 18-electron configuration can behave similarly. In our work, carried out between 1974 and 1983, we showed that half-sandwich type complexes [(CnRn)M(L)(PR3)] with n=5 (M=Co, Rh) and n=6 (M=Ru, Os), and L=CO, C2H4, C2R2, P(OR)3 etc., possess a Lewis basicity comparable to the Vaska compounds and react with electrophiles by attack at the metal center and not at one of the ligands. Complexes such as [(C5R5)M(PMe3)2] (R=H, Me; M=Co, Rh) are basic to the extent that they react with the weak acid NH4+ even at −78 °C by protonation at the metal. The review gave an up-to-date summary about the progress in this field.
- 4“Closing the Gap between MC3 and MC5 Metallacumulenes: The Chemistry of the First Structurally Characterized Transition-Metal Complex with MCCCCR2 as the Molecular Unit”: K. Ilg, H. Werner, Chem. Eur. J. 2002, 8, 2812–2820. After having prepared metallacumulenes of the type trans-[MCl(L)(PiPr3)2] with M=Rh, Ir, and L=CCR2, CCCR2, and CCCCCR2, which undergo CC, CO, CN, and CP coupling reactions under mild conditions, it became a real challenge to prepare the missing link in the chain with L=CCCCR2. An additional stimulus was that at that time no single complex with such a C4R2 ligand, which is extremely labile in the free state, had been structurally characterized. Kerstin Ilg developed an ingenious, in hindsight simple, method to generate the cumulated C4 chain at the iridium atom, and she confirmed by X-ray crystal-structure analysis that the MC4 unit is almost perfectly linear. Unexpectedly, reactions of trans-[IrX(C4Ph2)(PiPr3)2] (X=CH3, N3) with CO did not lead to an insertion of CO but to an insertion of the C4Ph2 cumulene into the IrCH3 or IrN3 bond.
10.1002/1521-3765(20020617)8:12<2812::AID-CHEM2812>3.0.CO;2-C CAS PubMed Web of Science® Google Scholar
- 5“The Truly Symmetrical Doubly-Bridging Mode of Trimethylphosphine in a Dinuclear Rhodium Complex”: T. Pechmann, C. D. Brandt, H. Werner, Chem. Commun. 2003, 1136–1137. In textbooks of inorganic and coordination chemistry it was frequently stated that, in contrast to CO and isocyanides, tertiary phosphines, which belong to the most well known ligands for low-valent transition-metal complexes, can coordinate to metal atoms only in a terminal but not in a bridging way. Based on previous results by Peter Schwab, Thomas Pechmann (my last PhD student) showed in the first part of his thesis (see Angew. Chem. 2000, 112, 4069–4072; Angew. Chem. Int. Ed. 2000, 39, 3909–3911) that in the dinuclear complex [Rh2(μ-CPh2)2(PMe3)(acac)2] the phosphine ligand occupies a bridging position. It was somewhat unsatisfactory, however, that in this compound the two bond lengths RhP differed by approximately 0.3 Å, which left some doubt whether the behavior of PMe3 as a ligand is exactly comparable with that of CO and CNR. In a rather elegant approach, Thomas succeeded in displacing the chelating acetylacetonato ligands by chloride ions and to isolate the complex [Rh2Cl2(μ-CPh2)2(μ-PMe3)], in which the Rh–P distances are equal and thus the phosphine is linked in a truly symmetrical doubly bridging mode to the rhodium atoms.
