Editor's Page pubs.acs.org/Organometallics
Editorial for the Mike Lappert Commemorative Issue
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motivating, and if this characteristic was present, persistence would eventually yield results. Overall, Mike’s direction tended to be low-key. He was very observant, however, and had a great sense of humor combined with a mastery of understatement in offering suggestions. He was essentially a private person, and at that time the group was generally unaware of several aspects of his life remote from chemistry: for example, his fluency in German and the tragic nature of his early life. Yet, the overall impression of him was one of warmth, and not remoteness. On the social side, there were frequent parties, as well as eagerly anticipated twice-yearly receptions at Mike’s home, with vast amounts of food and drink, hosted by his aunt Louise GrossLappert. At group meetings there was an emphasis on keeping accurate records and staying up to date with the literature, with frequent discussion of important new papers. A student summarized their work, and there was often discussion that produced several suggestions (usually helpful) on what to do next. Mike’s role at these was more that of a secretary who took notes while offering suggestions. At these meetings, one became aware of how broad his research interests were. A meeting might have students and postdocs describing their work on transition metal carbene complexes derived from electron-rich olefins (dimers of NHCs), transition metal alkyls, persistent main group radicals, hydrosilylation, photoelectron spectroscopy, or a derivative of cobalamin. As a result of the variety of his research in various blocks of the periodic table, Mike was often at pains to emphasize common patterns in the new compounds that were isolated. This is well-illustrated by his use of the −CH(SiMe3)2 ligand, which he introduced in the early 1970s, to stabilize lowcoordinate main-group, transition-metal, and lanthanide alkyls. Stable transition-metal and lanthanide alkyls were little-known at the time, although the related amido −N(SiMe3)2 ligand (isoelectronic with CH(SiMe3)2) had been used by Ulrich Wannagat, Don Bradley, and their co-workers to obtain lowcoordinate transition-metal derivatives.6,7 The recognition that certain alkyl ligands, which carried no β-H substituents and which were sufficiently sterically demanding, could stabilize metal alkyls that were otherwise prone to decomposition, occurred in 19698 with the publication of a patent. This was more extensively articulated in journal publications beginning in 1970.9 Simultaneously, Geoffrey Wilkinson recognized independently the same ligand characteristics with the synthesis of several homoleptic early-transition-metal derivatives.10 Many of the initial results in the area focused on the less bulky −CH2SiMe3 ligand, which proved particularly useful for the synthesis of stable four-coordinate transition metal derivatives, as well as stable lanthanide alkyls.11 In contrast, the larger −CH(SiMe3)2 ligand had just been shown to stabilize three-coordinate transition metal12 com-
ike Lappert, who died as a result of a tragic accident on March 28th, 2014, was one of the most influential of organometallic chemists. His work has had a profound and wide-ranging effect on the field. Almost uniquely, his work touched on and stimulated chemistry in every block of the periodic table. The diverse themes of this commemorative volume of Organometallics, incorporating over 70 papers by more than 300 distinguished authors, are a fitting tribute to the extent of his accomplishments. These have, in fact, been the subject of a number of previous tributes,1−5 the most recent of which was published by Dalton Transactions in late 2014 and which provided the most wide-ranging summary of his work, including a selection of over 30 of his scientific articles.5 The selected papers, which were chosen by the authors, in part on the basis of their citation frequencies, aptly demonstrate the broadness of his research interests. In this short perspective, another detailed account of his numerous accomplishments would involve much repetition. However, as someone who was associated with him as a Ph.D. (DPhil at Sussex) student, colleague, and sporadically a collaborator over a period of 40 years, this author, who arrived in the Lappert lab at University of Sussex in mid-October 1974, can offer a brief perspective on his group in the mid-1970s. In that era, Sussex was a world-class center for research in organometallic chemistry. As a naı̈ve beginner, I was made very welcome by Mike and all members of his group, and, just as importantly, given much practical help in getting started in the lab. Initiation into the research was also eased by the fact that, at that time, the department offered “crash” courses (introduced earlier by Colin Eaborn) in which a subject (in this case main-group organometallic chemistry) was crammed into a period of a few weeks. The instructors were Mike himself, Colin Eaborn, David Smith, David Walton, and John Nixonan impressive list. Mike suggested work on the lower valent amido derivatives of the group IVb (i.e., group 14) elements, which had just been discovered. Virtually all work in the lab involved air-sensitive compounds and was carried out using Schlenk techniques. It may surprise some workers today that Mike’s group did not have a dryboxa fact which renders their synthetic accomplishments all the more impressive. It is also worth remarking that the lab routinely synthesized all its own organolithium reagents, including BunLi! Fortunately, Mike asked a highly skilled and patient student, David Harris (to whom I owe much), to be the mentor who initiated me into the mysteries of handing really air-sensitive compounds. It soon became apparent that Mike’s group was an informal but wellknit team who were short on ceremony and long on esprit, imagination, and practical skills. This was really a reflection of Mike’s own personality. Laboratory hours were flexible to say the least, and although Mike visited the lab fairly frequently during the week (in between travels), it was to chat and offer encouragement and suggestions, rather than an attendance check. The group was a highly industrious one whose members often worked irregular hours. There was no sense of pressure, for it was his strong belief that the student should be self© 2015 American Chemical Society
Special Issue: Mike Lappert Memorial Issue Received: February 9, 2015 Published: June 8, 2015 2035
DOI: 10.1021/acs.organomet.5b00113 Organometallics 2015, 34, 2035−2036
Organometallics
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plexes such as M{CH(SiMe3)2}3 (M = Ti, V, Cr).12 Later it was shown to be equally effective in stabilizing three-coordinate lanthanides.13 Application of the CH(SiMe3)2 ligand to the main-group elements afforded many hitherto unknown types of compoundsfor example, the first stable two-coordinate, divalent :MR2 (M = Ge, Sn, Pb) species, which are analogous to carbenes.14 However, it was found that these divalent species are weakly dimerized in the solid state (similar to the case for the olefins), but with the important distinction that they had pyramidalized rather than the expected planar group 14 element geometry by analogy with their carbon-based analogues.15 These species provided evidence of the very different character of multiple bonding between two heavier pblock elements. This discovery exerted a profound influence on subsequent developments and heralded what turned out to be a very large and exciting field, involving the synthesis and characterization of stable compounds with multiple bonds between most of the heavier p-block elements. The investigation of whether or not the heavier carbene analogues existed in the singlet or triplet state led to another unanticipated discovery. EPR spectra of their solutions showed that they displayed weak signals attributable to the species • M{CH(SiMe3)2}3 (M = Ge, Sn).16 The intensity of the signals was greatly enhanced by photolysis. Moreover, it was found that these and related sterically crowded radicals were remarkably persistent, having half-lives of several months or years, thus blurring not only the distinction between the terms persistent and stable but also the standard distinction between complexes such as Ti{CH(SiMe3)2}3 as paramagnetic species and compounds such as Sn{CH(SiMe3)2}3 as radicals. Shortly afterward, this concept was extended to include radicals of phosphines and arsenic, with crucial input from a sabbatical visitor, Harold Goldwhite from California State University Los Angeles.17 Subsequently at Sussex, Colin Eaborn, David Smith, and co-workers showed, in an extensive series of papers, that the related, but more crowding, −C(SiMe3)3 alkyl group was highly effective in the stabilization of many new species and was particularly useful in the isolation of two-coordinate metal derivatives, many of which were the first examples of their kind.18 It would be fair to say that a sizable fraction of late 20th and early 21st century organometallic main-group chemistry incorporated aspects of one or other of these research themesthe synthesis and chemistry of stable main-group species with multiple bonds between heavier elements or of compounds with open-shell or paramagnetic electron configurations. Research in these areas not only generated many exciting new types of compounds but also resulted in major new insights in our understanding of bonding. The underlying approach involved essentially exploratory synthesis, with the general object of obtaining compounds with hitherto unknown structures, bonding, and reactivity. The record underlines the effectiveness of Mike’s approach. The initial groundbreaking results of Mike Lappert’s group in these areas stemmed mainly from the imaginative but simple use of a common ligand across the p, d, and f blocks. The effectiveness of the strategy underlines the broadness of his vision and the penetrating insight of this remarkable man.
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AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. The authors declare no competing financial interest.
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REFERENCES
(1) Cardin, D. J. Inorg. Chim. Acta 2007, 360, 1245 DOI: 10.1016/ j.ica.2006.08.023. (2) Nixon, J. F. Obituary: Professor Michael Lappert. University of Sussex [Online] April 4 2014. http://www.sussex.ac.uk/internal/ bulletin/staff/2013-14/04042014/mikelappert. (3) Leigh, G. Mike Lappert: Scientist who fled the Nazis as a child and went on to become one of the world’s leading inorganic chemists. http://www.independent.co.uk/news/obituaries/mike-lappertscientist-who-fled-the-nazis-as-a-child-and-went-on-to-become-one-ofthe-worlds-leading-inorganic-chemists-9502856.html (accessed 30 March 2015). (4) Power, P. P. Angew. Chem., Int. Ed. 2014, 53, 6857 DOI: 10.1002/ anie.201404980. (5) Arnold, J.; Brothers, P. J.; Mountford, P.; Piers, W. E.; Thomas, C. M.; Tilley, T. D. Dalton Trans. 2014, 43, 16553 DOI: 10.1039/ c4dt90167c. (6) Bürger, H.; Wannagat, U. Monatsh. Chem. 1963, 94, 1007 DOI: 10.1007/BF00905688. (7) Bradley, D. C.; Hursthouse, M. B.; Rodesiler, P. F. Chem. Commun. 1969, 14 DOI: 10.1039/C29690000014. (8) Collier, M. R.; Kingston, B. M.; Lappert, M. F.; Truelock, M. M. Organo-Metallic Compounds. U.K. Patent GB126554(A), 17 July 1969. (9) Collier, M. R.; Lappert, M. F.; Truelock, M. M. J. Organomet. Chem. 1970, 25, C36 DOI: 10.1016/S0022-328X(00)86195-1. (10) Yagupsky, G.; Mowat, W.; Shortland, A.; Wilkinson, G. Chem. Commun. 1970, 1369 DOI: 10.1039/C29700001369. (11) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 126 DOI: 10.1039/C39730000126. (12) Barker, G. J.; Lappert, M. F. J. Organomet. Chem. 1974, 76, C45 DOI: 10.1016/S0022-328X(00)87391-X. (13) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G.; Bartlett, R. A.; Power, P. P. J. Chem. Soc., Chem. Commun. 1988, 1007 DOI: 10.1039/ C39880001007. (14) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1973, 317 DOI: 10.1039/C3973000317A. (15) Goldberg, D. E.; Harris, D. H.; Lappert, M. F.; Thomas, K. M. J. Chem. Soc., Chem. Commun. 1976, 261 DOI: 10.1039/C39760000261. (16) Davidson, P. J.; Hudson, A.; Lappert, M. F.; Lednor, P. W. J. Chem. Soc., Chem. Commun. 1973, 829 DOI: 10.1039/C39730000829. (17) Gynane, M. J. S.; Hudson, A.; Lappert, M. F.; Power, P. P. J. Chem. Soc., Chem. Commun. 1976, 623 DOI: 10.1039/C39760000623. (18) Eaborn, C.; Smith, J. D. J. Chem. Soc., Dalton Trans. 2001, 1541 DOI: 10.1039/B100741F.
Philip P. Power
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DOI: 10.1021/acs.organomet.5b00113 Organometallics 2015, 34, 2035−2036
