Editor's Page pubs.acs.org/Organometallics
Legacy of Richard Heck
O
Palladium chemistry is now synonymous with Professor Heck’s name. Indeed, he and his colaureates Professor Ei-ichi Negishi and Professor Akira Suzuki were awarded the Nobel Prize for their contributions in this area. Heck’s early forays into organometallic chemistry, however, focused on another metal entirely. Beginning in the late 1950s, Heck began to study cobalt-catalyzed hydroformylation. Although at the time this was already emerging as an industrially important process, almost nothing was known about the mechanistic underpinnings of the reaction. In a now classic series of publications in the Journal of the American Chemical Society, he described the preparation, isolation, and characterization of a series of cobalt alkyl and acyl complexes.2 These studies, combined with investigations of the stoichiometric and catalytic reactivity of the complexes, allowed him to formulate the mechanism of hydroformylation. This early example demonstrates a mechanistic understanding of an organometallic process, and the details of his proposal are still taught largely unmodified in the classroom today. Following this groundbreaking work, Heck then published numerous outstanding publications developing new chemistry based upon cobalt catalysis. In his writing and in lectures given later in life,1 Heck devoted nearly equal time and importance to his work on cobalt chemistry as he did to the palladium chemistry that would bring him such renown later on. As a tribute to Heck’s important contributions to cobalt chemistry, this ACS Select collection includes the outstanding article by Harrison, Daniels, Korobkov, and Baker describing a new route to perfluoromethylated [Co(CO)4(CF3)].3 Indeed, more than 50 years after Heck and others began to develop chemistry to access these cobalt alkyl complexes, the compounds remain of significant interest in modern organometallic chemistry. The described route greatly simplifies access to this compound, allowing entry to new fluorinated cobalt alkyl complexes. After exploring cobalt chemistry for the better part of a decade, Heck became interested in the stability and reactivity of organopalladium complexes. These studies laid the foundation for the chemistry that ultimately led to the development of the modern “Heck Reaction”. In 1968, as he exited Hercules, Heck published a remarkable series of seven back-to-back articles in the Journal of the American Chemical Society.4 Among the discoveries reported were the first stoichiometric and catalytic examples of alkene arylation using organometallic reagents and very early examples of catalytic allyl chloride nucleophilic arylation (both with aryl mercurial compounds). In addition, these publications included early catalytic carbonylation studies, as well as carbohalogenation reactions, among others. These contributions were an absolutely extraordinary body of work, particularly considering that Heck was the sole author on all seven! In early 1972, in his first publication after moving to the University of Delaware, Heck and his colleague Nolley
n October 10th, 2015, Professor Richard F. Heck, 2010 Nobel Laureate and discoverer of the palladium-catalyzed transformation that bears his name, passed away at the age of 84. For those involved in the field of chemistry, and in particular those who study organometallics and the interface of organic and inorganic chemistry, we lost one of the great pioneers of our times. Professor Heck’s discoveries, along with those of a cadre of early organopalladium chemists, mark the foundation on which a vast area of catalytic and preparative organic chemistry now stands. Almost 50 years after the initial publications began to emerge, this area remains an active and important area of chemical research. Professor Heck helped establish this burgeoning field. Indeed, more than 40 years after the initial reports of what we now know as the “Heck Reaction”, and more than 25 years since his retirement from the University of Delaware, the field of catalytic organometallic chemistry, and organopalladium chemistry in particular, continues to grow at an incredible pace and expand in importance. Today, multiple industriesfrom pharmaceuticals to personal care products to performance materialsare dependent on technologies that have followed from the work of Richard Heck and his fellow pioneers. This ACS Select virtual issue, which includes recent publications from Organometallics, as well as The Journal of Organic Chemistry, the Journal of the American Chemical Society, and Organic Letters, has been organized to pay tribute to the legacy of Professor Heck. We hope that, by highlighting several recent publications from these journals, we will illuminate some of the areas of research he helped to define. We have attempted not only to select publications that embody his direct legacy in terms of chemistry reported but also to identify articles that reflect the sprit in which he conducted his own research. To this end, we have chosen to focus on contributions that highlight the interplay of mechanistic and/or structural insight and the development of synthetic methods, a hallmark of Heck’s own publications. Notably, however, Heck’s efforts were so large, and his impact so wide, that it is impossible to even begin to provide a complete selection of publications that fully captures what he did for this field. Without doubt, there are countless more articles that could have been included and would honor Heck’s deep and profound legacy. Heck entered organometallic chemistry just as the field was developing. Although some, mostly heterogeneous, industrial processes were known that utilized transition metals as catalysts, the chemical world was just beginning to think about the nature of the carbon−metal bond and the potential ways compounds containing them could be exploited. As Heck recounted in a short account published in 2006, he joined the Hercules Powder Company, in Wilmington, Delaware, after having received Ph.D. and postdoctoral training in physical organic chemistry.1 In his new role at Hercules, Dr. Heck was given the less-than-insightful instructions “do something with transition metals”.1 He clearly took this sage advice to heart, as it defined his career for the next 30 years. © 2016 American Chemical Society
Published: May 9, 2016 1177
DOI: 10.1021/acs.organomet.6b00261 Organometallics 2016, 35, 1177−1178
Organometallics
Editor's Page
described what would become known as the Heck Reaction the palladium-catalyzed vinyl- or arylation of alkenes using vinyl and aryl halides.5 This finding represented a remarkable improvement over the earlier version of the reaction, as it eliminated the need for toxic mercury reagents. As Heck acknowledged, they were beaten to publication by Mizoroki and co-workers, who published a similar protocol a few months before.6 From that point forward, Heck devoted his efforts to the development of this and related palladium-catalyzed transformations. These studies not only defined the Heck Reaction, but also inspired generations of other scientists to develop related cross-coupling reactions. The remaining Organometallics publications in this ACS Select collection pay homage to Professor Heck’s efforts in palladium chemistry. Two of these articles highlight outstanding studies that employ physical organometallic chemistry as a tool to better understand and develop synthetic methodology in crosscoupling reactions. The first, by Guest, Menezes da Silva, de Lima Batista, Roe, Braga, and Navarro, highlights the complexities of additives and counterions in Heck reactions.7 The second article, from Aufiero, Scattolin, Proutière, and Schoenebeck, systematically studies the use of palladium(I) dimers in Kumada-type cross-coupling reactions.8 The study by Miloserdov, McMullin, Belmonte, BenetBuchholz, Bakhmutov, Macgregor, and Grushin highlights another very important type of process discovered by Heck: the carbonylation of aryl halides.9,10 Typically, these reactions are used to prepare aromatic amides and esters; however, this report describes the development of conditions to directly access highly useful aroyl azides. Much in the vein of both the papers described above, as well as in Heck’s own work, this study is a beautiful example of using structural and stoichiometric studies to develop new and highly useful chemistry through a fundamental understanding of the underlying organometallic chemistry. The review by Gildner and Colacot highlights the enormous advancements that have been made within palladium-catalyzed cross-coupling reactions in the last 20 years, particularly with respect to catalyst development and ligand design.11 Ligand design and precatalyst development now allow for processes that were unthinkable only a few years back. Although many of the reactions within the review are not classically thought of as “Heck Reactions”, there is a clear and discernible intellectual lineage that can be traced back to the work of Heck and other early pioneers. Moreover, it is fitting to highlight a review on ligand design when honoring Heck, as he was one of the first to recognize the importance of ligands within these classes of reactions, pioneering the use of both triphenylphosphine,10a and later tri(o-tolyl)phosphine,12 in reactions of aryl bromides. Finally, the article by Katcher, Norrby, and Doyle serves to highlight the sheer breadth of palladium-catalyzed processes that have and continue to be developed since Heck’s studies.13 This elegant publication describes studies to define the mechanism of nucleophilic fluorination of allyl chlorides. This transformation is notable not only for the important fluorinated organic compounds produced but also because until recently such reactions were not thought to be possible. Although much progress, innovation, and ingenuity were required to develop this process, the inspiration for the underlying concepts of the transformation can be traced back to work by Heck, and his contemporaries, in the early descriptions of catalytic nucleophilic substitution of allylic halides.4c
A wealth of research that builds on Heck’s contributions has been published in sister ACS journals and publications from The Journal of Organic Chemistry, the Journal of the American Chemical Society, and Organic Letters were selected for inclusion in this ACS Select virtual issue as well. It clear is that Richard Heck’s impact on the field of organometallic chemistry and organic synthesis is difficult to overstate. In so many ways, and for so many generations of scientists, his work has served both to create and to inspire. What may be less well appreciated, however, is the modesty with which Professor Heck worked and lived. As a faculty member at the University of Delaware, I have the honor of working in the academic department where Heck developed his now famous reaction. Although Professor Heck had long since become emeritus by the time that I arrived on campus, I was able to interact with him on a fewbut personally very preciousoccasions. I will always remember his response when I attempted to simply thank him for all that he had contributed to our field and let him know how inspirational his work was to me personally. He simply replied, “I am glad that I was able to do something someone found valuable.” I was stunned by how humble and ridiculously understated his words were. Many of my colleagues who taught and led research groups alongside Professor Heck have similar stories. They speak of a gentle, unassuming man, who was driven only by his curiosity and a deep desire to do something useful for the world. We can be certain that he accomplished that goal, and thankful that he did so while doing “something with transition metals”.
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Donald A. Watson, Guest Editor AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Heck, R. Synlett 2006, 2006, 2855. (2) (a) Heck, R. F.; Breslow, D. S. J. Am. Chem. Soc. 1960, 82, 750. (b) Heck, R.; Breslow, D. J. Am. Chem. Soc. 1960, 82, 4438. (c) Heck, R.; Breslow, D. J. Am. Chem. Soc. 1961, 83, 4023. (d) Heck, R.; Breslow, D. J. Am. Chem. Soc. 1961, 83, 1097. (3) Harrison, D. J.; Daniels, A. L.; Korobkov, I.; Baker, R. T. Organometallics 2015, 34, 4598. (4) (a) Heck, R. J. Am. Chem. Soc. 1968, 90, 5518. (b) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5526. (c) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5531. (d) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5535. (e) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5538. (f) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5542. (g) Heck, R. J. Am. Chem. Soc. 1968, 90, 5546. (5) Heck, R.; Nolley, J. J. Org. Chem. 1972, 37, 2320. (6) Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581. (7) Guest, D.; Menezes da Silva, V. H.; de Lima Batista, A. P.; Roe, S. M.; Braga, A. A. C.; Navarro, O. Organometallics 2015, 34, 2463. (8) Aufiero, M.; Scattolin, T.; Proutiere, F.; Schoenebeck, F. Organometallics 2015, 34, 5191. (9) Miloserdov, F. M.; McMullin, C. L.; Belmonte, M. M. n.; BenetBuchholz, J.; Bakhmutov, V. I.; Macgregor, S. A.; Grushin, V. V. Organometallics 2014, 33, 736. (10) (a) Schoenberg, A.; Bartoletti, I.; Heck, R. F. J. Org. Chem. 1974, 39, 3318. (b) Schoenberg, A.; Heck, R. F. J. Org. Chem. 1974, 39, 3327. (c) Schoenberg, A.; Heck, R. F. J. Am. Chem. Soc. 1974, 96, 7761. (11) Gildner, P. G.; Colacot, T. J. Organometallics 2015, 34, 5497. (12) Ziegler, C. B.; Heck, R. F. J. Org. Chem. 1978, 43, 2941. (13) Katcher, M. H.; Norrby, P.-O.; Doyle, A. G. Organometallics 2014, 33, 2121.
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DOI: 10.1021/acs.organomet.6b00261 Organometallics 2016, 35, 1177−1178
