Ernesto Carmona: Organometallic Chemistry Pioneer in Southern

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Ernesto Carmona: Organometallic Chemistry Pioneer in Southern EuropeA Biographical Outline

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ith this issue, Organometallics celebrates the career of Professor Ernesto Carmona on the occasion of his 70th birthday this year (Figure 1). Ernesto is one of the best-known names in our field and is definitely one of the important figures in chemistry during the launch of Spanish science in the second half of the 20th century. This Special Issue collects contributions from colleagues active in our field who have had some significant personal or scientific link with Ernesto. In addition to this Special Issue, a symposium in Seville has been organized by some of his former students, with some of Ernesto’s closest scientific colleagues acting as speakers.1 Responses to the requests to participate in this homage have been almost invariably positive, often enthusiastican additional sign of Ernesto’s international recognition. Therefore, to increase opportunities for other colleagues to join the Organometallics Special Issue tribute, the symposium organizers voluntarily decided to publish their dedicated articles in regular issues of Organometallics and other journals. Otherwise, this Special Issue depicts a broad panorama of the current state of the field of organometallic chemistry. However, prior to introducing its contents, it is pertinent to dedicate a few lines to describe Ernesto’s character and career development. Ernesto Carmona was born in Seville in 1948 and completed his chemistry studies in the local university, the Hispalense, in 1972. Seville is the principal city of southern Spain and arguably the ultimate archetype of Spain as a picturesque romantic place, full of folklore and bizarre traditions, but a place far removed from the intellectual and scientific endeavors of her fellow European nations. Doubtless, this is merely a common viewpoint, yet one that was very much a reality at the time of Ernesto’s birth and early years, in contrast to what it is today. Echoes of a long, historic period of political decadence, social turbulence, and misgovernment were still evident in the country’s economic underdevelopment. However, winds of change were beginning to blow, brought about by political stability and economic prosperity. Sailing on such a gentle breeze, social advances and education experienced a boom during the late 1970s and throughout the 1980s. One of the most spectacular effects of the sociopolitical process, known as The Spanish Transition, but not fully realized at that time, and maybe not as much as it ought to be by today’s rulers, was the establishment of a regular system of science and technology in Spanish universities. Ernesto is one of the representative figures of that period of scientific renaissance, to which he personally contributed in no small amount by creating a first-magnitude school of organometallic chemistry essentially from the ground up at the University of Seville. In the early 1970s, research in Seville’s Department of Inorganic Chemistry focused largely on classic topics of mineral chemistry, such as silicates and soil science. However, Ernesto’s reading of modern textbooks drove his interests © 2018 American Chemical Society

toward molecular inorganics: transition-metal complexes and organometallic compounds. It is an interesting circumstance that the field of inorganic chemistry had just undergone its own sort of renaissance, according to Ronald Nyholm.2 The evolution of inorganic chemistry from what, in Nyholm’s words, was a “dull and uninteresting state” into the lively science that it is today took place during the middle of the 20th century, brought about by the research efforts driven by World War II. The subsequent discoveries of Ziegler−Natta polymerization catalysts3 and of ferrocene and the whole family of sandwich complexes,4 a somewhat deprecated term nowadays in favor of the more technical “metallocene”, opened up a new and exciting frontier in the emerging field of organotransitionmetal chemistry. In fact, the discovery of ferrocene is usually regarded as the birth of organometallic chemistry. Thus, it came to pass that, after completing brief research work on coordination chemistry for his Ph.D., Ernesto moved to London in 1974 to join Geoffrey Wilkinson’s group at Imperial College. There he was to acquire the knowledge and skills that he needed before he could start his independent career. Ernesto had met Wilkinson for the first time in 1973,5 barely a few months before the latter was awarded the Nobel Prize for the elucidation of the structure and bonding in ferrocene. The stay at Imperial College London lasted some four years, a long period for postdoctoral work, even by today’s standards. At that time, postdoc stays abroad were quite unusual in Spanish scientific circles. However, with support from the influential head of Seville’s Department of Inorganic Chemistry, Francisco González Garcia,́ Ernesto gained one of the few mobility grants made available by the British Council for Spanish students. The beginnings in London were not easy for Ernesto, as he had yet to learn everything about organometallic chemistry. Moreover, the meager grant stipend allowed hardly a subsistence for him and his young wife, especially during the first months. Eventually, the economic situation improved, and these years left many happy memories; the main one was the birth of their first son. The first project that Wilkinson assigned Ernesto dealt with the syntheses of σ-alkyl derivatives of transition metals, a problem that had challenged inorganic chemists for a long time and had by then become an important research topic.6 Among other results, Ernesto succeeded in isolating and crystallizing some of the first examples of extremely air and moisture sensitive Mn(II) dialkyl derivatives.7 Then he investigated the chemistry of reduced molybdenum and tungsten complexes with tertiary phosphines. Ernesto’s success in difficult tasks won him the respect and esteem of Sir Geoffrey, but no doubt it was his magnetic personality that gained him lifelong friendship with many of his Special Issue: In Honor of the Career of Ernesto Carmona Published: October 22, 2018 3379

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Figure 1. Portrait of Professor Ernesto Carmona with a portrait of G. Wilkinson. Photo credit: Práxedes Sánchez.

The focus on the organometallic chemistry of nickel was also a distinct feature of the Seville group. Following Ziegler’s discovery of the so-called nickel effect11 in the early 1950s, the chemistry of organonickel compounds had experienced an impressive development. However, almost a quarter of a century later, the impetus had decayed in favor of the study of the organometallic compounds of the heavier group 10 congeners palladium and platinum, as their usually more stable nature and applications in catalysis provided an attractive field of research. Ernesto’s work on organonickel compounds focused on the reactivity of σ-Ni−C bonds toward CO, CO2, and other unsaturated molecules.12 The research team found that basic phosphines such as PMe3 promote facile i n t r a m o l e c u l a r C − H ac t i v a t i o n o f t h e n e o p h y l (−CH2CMe2Ph) alkyl group.13 This achievement opened the way to the study of the fascinating reactions of the resulting nickelacycles, often leading to interesting or unusual organic molecules.14 However, the research was not limited to the reactivity of Ni−C bonds, and pioneering work was carried out on insertion reactions into the reactive Ni−O linkages in molecular organonickel hydroxides.15 Ernesto’s interest in C−H activation led him to start a new research line dealing with the organometallic chemistry of iridium and rhodium complexes. Inspired by the seminal papers published in 1982 by the Bergman and Graham groups on alkane activation by the iridium complexes (η5-C5Me5)IrH2(L) and (η5-C5Me5)Ir(R)H(L),16 the Seville group embarked on the study of the reactivity of similar compounds supported by tris(pyrazolyl)borates (Tp ligands).17 This proved to be an extremely prolific research pathway, leading to the discovery of many “cascade” reactions in which consecutive steps, often employing intermediate C−H or C− O bond activations, enchain one to the other to perform complex transformations of organic substrates.18 Ernesto has always been fonder of research and university teaching than of leadership positions in science. However, his international recognition and reputation as an honest and

fellow lab mates, some of whom were to become luminaries in the field: Richard Andersen, David Cole-Hamilton, Roberto Sánchez-Delgado, Bruno Chaudret, and Manfred Bochmann. He also had occasion to meet Malcolm Green, one of Wilkinson’s earliest disciples. Years later, when Ernesto was already Professor of Inorganic Chemistry in Seville, Green invited him to spend a sabbatical year as a Visiting Professor at Oxford University. This represented a major milestone in Ernesto’s career. Thus, the intellectual and human capital that he gained during his years in Britain have marked to large extent his scientific development. Ernesto returned to the University of Seville in 1977, where he established his own research group and gained tenure as full professor in 1984. It is worth mentioning that, at that time, Ernesto’s group was the only one in Spain not linked to the important school in organometallic chemistry born at the University of Zaragoza in the mid-1960s, which had spread to several other universities across the country. However, the southern stem of the Spanish tree of organometallic chemistry that sprouted in Seville was to prove, very soon, to be a vigorous and prolific one. The chemistry developed in Seville carried a distinctive imprint, inherited from Wilkinson’s lab. In these early years, Ernesto’s research dealt with the synthesis of electron-rich σorganometallic complexes of molybdenum, tungsten, and nickel stabilized with highly basic alkylphosphines, chiefly PMe3, which was regularly prepared in house on a respectable 2 mol scale. Started in the context of the first oil crisis, these investigations pursued the study of activation of small molecules by the reactive metal complexes.8 One of the relevant results was the assembly of an acrylate ligand from ethylene and carbon dioxide, effected by the low-valent molybdenum and tungsten phosphine complexes, which became a landmark in the field of CO2 activation.9 The group also devoted much attention to the study of the insertion chemistry of CO.10 Results from this important work frequently put Ernesto’s small group under the spotlight. 3380

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observation led Ernesto’s group to undertake the challenge of preparing decamethylberyllocene (BeCp*2), a molecule that had been predicted to be unstable because of the size mismatch between the small beryllium cation and the bulky Cp* ligands. This brave decision met with success, and the target complex was obtained after refluxing BeCl2 with KCp*. Surprisingly, the crystal structure of BeCp*2 turns out to lack any “slippage” and exhibits the classic staggered D5d symmetry characteristic of a η5/η5 structure, like that of ferrocene.21 Seeking a rationale for these puzzling structural trends, Ernesto turned to examine the structures of similar zinc metallocenes with various substitution patterns.22 This work put him on the path to what was to be one of the most remarkable achievements in his already brilliant career: the isolation and full characterization in 2004 of decamethyldizincocene, Zn2(η5-Cp*)2, the first example of a stable Zn(I) compound.23 This compound was first observed as an unexpected byproduct in the comproportionation reaction of decamethylzincocene Zn(η5-Cp*)2 with ZnEt2. The molecule of Zn2(η5-Cp*)2 is linear and contains a (Zn−Zn)2+ core, analogous to the dimercury cation Hg22+ found in many common Hg(I) compounds, such as mercurous chloride, or calomel, a molecular compound known since antiquity. The monovalent oxidation state is less frequent for cadmium, but a few molecular compounds were also known to contain the Cd22+ unit.24 The many unsuccessful attempts at preparing similar “zincous” molecular compounds led to the generalized credence that, aside from its elemental form, zinc exists exclusively in the divalent oxidation state. The abundant production of Ernesto’s group over the past decade covers a number of his classic research themes and some new ones. Considering his scientific trajectory, the most interesting trend is probably the leap from zinc−zinc singly bonded compounds to the study of transition complexes with high-order metal−metal bonds. This classic topic in molecular inorganic chemistry returned to the front line of our attention in 2005, when Philip P. Power of the University of California, Davis, reported on binuclear chromium aryls with formal quintuple bonds that pushed the limits of chemical bonding one step further.25 Research in Ernesto’s laboratory thus turned to developing the reactivity of molybdenum complexes with high-multiplicity metal−metal bonds. One of the most relevant results achieved was the interconversion between quadruple- and quintuple-bonded dimolybdenum cores through bimetallic reductive H2 elimination, and its reversal, the oxidative addition of H2 across the quintuple molybdenum−molybdenum bond.26 Throughout his career, Ernesto has always been a natural leader. In choosing his science projects, he has never been afraid to undertake the hottest topics in inorganic and organometallic chemistry, no matter their experimental difficulty. Often he led projects to success by showing students the value of systematic and rigorous work carefully performed to the last detail. However demanding he might be, Ernesto never ceases to show his human side to everyone that ever approaches him. Probably it is this attractive personality, his manner of pointing out the way to noble and important objectives, and his will to pursue the task indefatigably until the goal is accomplished that has always galvanized his co-workers to give their very best. Everyone who has joined Ernesto’s projects, or has had the opportunity to collaborate with him in some task, knows how easy it is to be seduced by his kind manners and bonhomie, being rapidly induced to emulate him

sensible person attracted many nominations and offers for posts of responsibility. Although these usually brought dull and heavy work, he never refused when he considered it his duty to accept. From these positions, he helped shape one of the most brilliant periods for science in Spain. In the 1990s, Ernesto played an important role in the creation of cicCartuja, a research center run jointly by the University of Seville, CSIC (the national research council of Spain), and the regional government of Andalusia. This center housed three research institutes, one of them the newly created Institute of Chemical Research (IIQ). In 1995, Ernesto became jointly the first head of cicCartuja and IIQ, to which he moved with his research group in 1996. At IIQ, his group would benefit from state of the art laboratories and equipment and, above all, the much-needed space for his group that had grown considerably by then. The years about the turn of the century were marked by Ernesto’s renewed interest in the chemistry of less investigated compounds of the metallocene family, a topic that brought him many remembrances of his days in Wilkinson’s lab. The beginnings of this project stemmed from some unsuccessful attempts to transfer Tp ligands to “exotic” elements such as tantalum, samarium, and the actinides uranium and thorium. This failure drove interest to the then rarely frequented chemistry of actinide metallocenes. At that time, he shared his interest in the organometallic chemistry of actinides with Andersen, a good friend since their times at Imperial College, whose group at the University of California, Berkeley, had shown that certain monomeric uranocenes behave as Lewis acids and form stable adducts with different bases. Pursuing this line of research, Ernesto’s group investigated the interaction of U(η5-C5Me4H)3 with nonclassical bases, such as carbon monoxide and isocyanides. This work led to the isolation of U(η5-C5Me4H)3(CO), the first carbonyl of an actinide that could be structurally characterized, as well as similar isocyanide adducts.19 The success in the isolation of these complexes was most likely the result of the particular choice of [C5Me4H]− ligand, whose size is perfectly adapted to the shape of the UCp3 fragment. A complete structural and spectroscopic investigation of the carbonyl and isocyanide adducts U(η5-C5HMe4)3(L) demonstrated beyond any doubt the ability of the 5f orbitals of the U(III) center to participate in a covalent interaction, back-donating part of the electron density of these orbitals into the empty π* levels of π-acceptor ligands. Promising as it was, the actinide research was discontinued after a few years, in part because of the difficulty in maintaining and managing a regular supply of weakly radioactive (238Udepleted) uranium and thorium under increasingly strict regulations. These problems shifted Ernesto’s interests from the actinides to the metallocene derivatives of the lighter alkaliearth elements, mainly to beryllium. Probably owing to the toxicity and lack of applications of this scarce element, the only beryllium metallocene reported up to 1999 was the parent BeCp2 itself, reported by Fischer 40 years before.20 The solid-state structure of this compound shows a peculiar geometry known as “slipped sandwich”, in which both Cp ligands are parallel, but one of them is shifted, allowing the beryllium atom to interact with just one carbon atom. When [C5Me4H]− replaces Cp, the resulting beryllocene also has the “slipped” structure, one of the C5Me4H groups showing the typical η5 coordination while the other has π:η1 coordination through the least hindered CH group. This 3381

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into how palladium complexes with BrettPhos-type ligands can be applied to either nitroarene activation (in Suzuki−Miyaura reactions) or haloarene nitration (DOI: 10.1021/acs.organomet.8b00199). In the same vein, Lledós and Ujaque describe a computational analysis of alkyne hydration catalyzed by [(NHC)Au] + cations (DOI: 10.1021/acs.organomet.8b00230). Ligands designed to render metal catalysts water-soluble, and their application in aqueous media, are the central topic of three articles from Spanish groups: Oro/Iglesias (iridiumcatalyzed formic acid dehydrogenation; DOI: 10.1021/ acs.organomet.8b00289), Crochet/Cadierno (isomerization of allyl ethers; DOI: 10.1021/acs.organomet.8b00187), and Otero/Fandos (water-soluble Cp*Ti complexes; DOI: 10.1021/acs.organomet.8b00209). Cuenca and Jiménez report on the application of Ti(IV) complexes with chiral ligands based on natural terpenes to perform sulfoxidation reactions with aqueous hydrogen peroxide (DOI: 10.1021/acs.organomet.8b00163). Tolerance in aqueous media is also important for the application of organometallic complexes as antitumor drugs. The article by Granell and Quirante provides some insight into the activity of cycloplatinated arylamine complexes in the treatment of cisplatin-resistant tumors (DOI: 10.1021/ acs.organomet.8b00206). Two more articles dwell on the intriguing effect of supramolecular association as a factor modulating the catalytic activity of organometallic complexes. Peris and Poyatos show that both the activity and selectivity of binuclear gold complexes with ditopic NHC ligands is boosted by host−guest association with flat PAH molecules (DOI: 10.1021/acs.organomet.8b00087). On the other hand, Weller and McGregor demonstrate that both the reactivity and selectivity of cationic rhodium catalysts in the solid state can be tuned by the counteranion, as the latter dictates the way in which crystals are assembled, generating different local microenvironments for the complex unit (DOI: 10.1021/ acs.organomet.8b00215).

as much as one can. This is the key to understanding the way in which Ernesto Carmona has exerted his leadership: by sowing, little by little, admiration and love in each one who was fortunate enough to have this great person for reference in his or her everyday work. This Special Issue is thus timely for taking the pulse of organometallic chemistry on the occasion of Ernesto’s 70th birthday. Fundamental studies have not lost impetus in the timespan of his long career and continue to bring novelty and innovation. One such trend is the use of rigid ligands as scaffolds to enable elusive chemical species to be isolated and characterized. Two articles, one by Kirchner (DOI: 10.1021/ acs.organomet.8b00193) and the second by Sabo-Etienne, Merino, and Montiel-Palma (DOI: 10.1021/acs.organomet.8b00269) describe complementary examples of pincer ligands to stabilize and characterize agostic and anagostic C− H···M interactions. More classic ligands such as the ubiquitous Cp* show their potential to gauge the trans influence of various donors L in a paper by Espinet and Bartolomé (DOI: 10.1021/acs.organomet.8b00227). Esteruelas describes unusual rearrangements of NHC-based chelates in osmium complexes (DOI: 10.1021/acs.organomet.8b00110), and Wolczanski reports on stepwise carbene addition to noninnocent chelate ligands in titanium complexes (DOI: 10.1021/acs.organomet.8b00188). Several articles in this issue deal with the reactivity of multiple-bonded ligands: oxygen atom transfer from nucleophilic terminal ReIIIO (Bergman and Arnold; DOI: 10.1021/acs.organomet.8b00238), addition of unsaturated molecules to terminal TiIVN−B borylimidos (Mountford; DOI: 10.1021/acs.organomet.8b00250) or to terminal methylidynes NbVCH (Mindiola; DOI: 10.1021/acs.organomet.8b00245), and the interplay between alkylidene and germylene ligands in Grubbs-type ruthenium methathesis ́ ́ lvarez; DOI: 10.1021/acs.organocatalysts (Cabeza/Garcia-A met.7b00905). The reactivity of multiple metal−metal ́ interactions is analyzed by Ruiz and Garcia-Vivó in their work on the addition of weak E−H electrophiles to a formal bond of a heterobimetallic MoRe carbonylate anion (DOI: 10.1021/acs.organomet.8b00129). CO2 insertion reactions, a favorite topic in Ernesto’s early research, are also well-represented in this issue. Organometallics’ Editor-in-Chief, Paul J. Chirik, reports the formation of a nickel acrylate complex arising from the reaction of CO2 with a highly unusual vinyl derivative stabilized with a singly reduced α-diimine ligand (DOI: 10.1021/acs.organomet.8b00350). This process is strongly reminiscent of Ernesto’s molybdenum acrylate synthesis by CO2/ethylene coupling.9 The importance of such a “dream reaction” in contemporary chemistry is highlighted in Bernskoetter’s article describing intermediates involved in catalytic CO2/ethylene coupling mediated by nickel-diphosphine complexes and the effect of additives and experimental conditions on the process (DOI: 10.1021/acs.organomet.8b00260). The role of ligands and ligand design in homogeneous catalysis is the topic of several articles as well. Albrecht describes implementation of the pyridylideneamide ligand system in palladium catalysts for olefin dimerization/isomerization (DOI: 10.1021/acs.organomet.8b00422), and Echevarren analyzes the impact of donor group variations on the structural motif of the bulky phosphine JohnPhos applied to Au(I) catalysts (DOI: 10.1021/acs.organomet.8b00276). Computational analyses by Nakao and Sakaki provide insight

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Juan Cámpora

AUTHOR INFORMATION

ORCID

Juan Cámpora: 0000-0001-7305-1296 Notes

Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Biography Juan Cámpora is a Research Professor in the Institute of Chemical Research (IIQ) in Seville, Spain. He did his Ph.D. thesis under the supervision of Ernesto Carmona and Manuel L. Poveda. In 1990, he was awarded a Fulbright fellowship to carry out a postdoctoral stay at MIT in the laboratories of Stephen L. Buchwald. In 1992, he returned to Sevilla and joined the newly created IIQ in 1996, becoming its director between 2000 and 2004. He has led his own research group at IIQ since 2005, focusing on the study of the role of well-defined organometallic compounds in catalytic processes of industrial relevance.

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REFERENCES

(1) Symposium in Honor of Professor Ernesto Carmona internet site: http://www.ecarmona70th.es. (2) (a) Nyholm, R. S. The Renaissance of Inorganic Chemistry. J. Chem. Educ. 1957, 34, 166−169. (b) Brock, W. H. The Fontana

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History of Chemistry; Fontana Press, Harper and Colllins Publishers: 1995; Chapter 15. (3) Wilke, G. Karl Ziegler  The Last Alchemist. In: Ziegler Catalysts: Recent Scientific Innovations and Technical Improvements; Fink, G.; Mülhaupt, R.; Britzinger, H. H., Eds.; Springer: 1995. (4) Werner, H. Landmarks in Organo-Transition Metal Chemistry, A Personal View. Springer: 2009; Chapter 5. ́ (5) Carmona, E. Los Metalocenos, Arquetipo de Familia Quimica. Lecture given on the occasion of his acceptance as a member of the Royal Academy of Sciences of Spain on April 25, 2007. Available free of cost on the Internet at http://www.rac.es/ficheros/Discursos/DR_ 20080825_153.pdf. (6) Cotton, F. A. Alkyls and Aryls of Transition Metals. Chem. Rev. 1955, 55, 551−594. (7) Andersen, R. A.; Carmona-Guzman, E.; Gibson, J. F.; Wilkinson, G. Neopentyl, neophyl and trimethylsilylmethyl compounds of manganese. Mn(II) dialkyls; Mn(II) dialkyl amine adducts; MnR42‑ ions and Li+ salts. Mn(IV) tetraalkyls. J. Chem. Soc., Dalton Trans. 1976, 2204−2211. (8) Á lvarez, R.; Carmona, E.; Marín, J. M.; Poveda, M. L.; GutiérrezPuebla, E.; Monge, A. Carbon dioxide chemistry. Synthesis, properties and structural characterization of stable bis(carbon dioxide) adducts of molybdenum. J. Am. Chem. Soc. 1986, 108, 2286−2294. (9) (a) Á lvarez, R.; Carmona, E.; Cole-Hamilton, D. J.; Galindo, A.; Gutierrez-Puebla, E.; Monge, A.; Poveda, M. L.; Ruiz, C. Formation of Acrylic Acid Derivatives from the Reaction of CO2 with Ethylene Complexes of Molybdenum and Tungsten. J. Am. Chem. Soc. 1985, 107, 5529−5531. (b) Á lvarez, R.; Carmona, E.; Galindo, A.; Gutierrez, E.; Marín, J. M.; Monge, A.; Poveda, M. L.; Ruiz, C.; Savariault, J. M. Formation of Carboxylate Complexes from the Reactions of CO2 with Ethylene Complexes of Molybdenum and Tungsten. X Ray and Neutron Diffraction Studies. Organometallics 1989, 8, 2430−2439. (10) (a) Carmona, E.; Sánchez, L.; Marín, J. M.; Poveda, M. L.; Atwood, J. L.; Priester, R. D.; Rogers, R. D. η2-Acyl coordination and β-C-H interaction in acyl complexes of molybdenum. Crystal and Molecular Structures of Mo(η2-COCH2SiMe3)Cl(CO)(PMe3)3 and [cyclic]-Mo(COCH3)(S2CNMe2)(CO)(PMe3)2. J. Am. Chem. Soc. 1984, 106, 3214−3222. (b) Carmona, E.; González, F.; Poveda, M. L. Alkyl and Acyl Derivatives of Nickel(II) Containing Tertiary Phosphine Ligands. J. Chem. Soc., Dalton Trans. 1980, 2108−2116. (c) Carmona, E.; Contreras, L.; Poveda, M. L.; Sánchez, L. J.; Atwood, J. L.; Rogers, R. D. η2-Acyl and Methyl Complexes of Tungsten. Crystal and Molecular Structures of W(η 2-C(O)CH2SiMe3)Cl(CO)(PMe3)3 and W(CH3)(S2CNMe2)(CO)2(PMe3)2. Organometallics 1991, 10, 61−71. (11) Fischer, K.; Jonas, K.; Misbach, P.; Stabba, R.; Wilke, G. The “Nickel Effect”. Angew. Chem., Int. Ed. Engl. 1973, 12, 943−953. (12) (a) Carmona, E.; Marín, J. M.; Paneque, M.; Poveda, M. L. New Nickel o-Methylbenzyl Complexes. Crystal and Molecular Structures of Ni(η 3 -CH 2 C 6 H 4 -o-Me)Cl(PMe 3 ) and Ni 3 (η 1 CH2C6H4-o-Me)4(PMe3)2(μ3-OH)2. Organometallics 1987, 6, 1757− 1765. (b) Carmona, E.; Paneque, M.; Poveda, M. L. Synthesis and characterization of some new organometallic complexes of nickel(II) containing trimethylphosphine. Polyhedron 1989, 8, 285−291. (c) Carmona, E.; Gutiérrez-Puebla, E.; Monge, A.; Marin, J. M.; Paneque, M.; Poveda, M. L. Formation of alkenyl ketone complexes and of dimeric α,β-butenolides by sequential insertion of phenylacetylene and carbon monoxide into nickel-acyl bonds. X-ray structures of [cyclic]-Ni[C(Ph)C(H)(COCH2SiMe3)]Cl(PMe3)2 and [cyclic]-Ni[C(Ph)(PMe3)C(H)(COCH2CMe2Ph)]Cl(PMe3). Organometallics 1989, 8, 967−975. (d) Carmona, E.; Palma, P.; Paneque, M.; Poveda, M. L. η1- and η2-Alkaneimidoyl Complexes of Nickel: Synthesis and Properties. Organometallics 1990, 9, 583−588. (13) (a) Carmona, E.; Palma, P.; Paneque, M.; Poveda, M. L.; Gutiérrez-Puebla, E.; Monge, A. Synthesis of [cyclic]-(Me3P)2Ni(CH2CMe2-o-C6H4) and its Reactivity toward Carbon Dioxide, Carbon Monoxide and Formaldehyde. First Observation of a Carbonyl-Carbonate Oxidative Comproportionation Mediated by a

Transition-Metal complex. J. Am. Chem. Soc. 1986, 108, 6424−6425. (b) Carmona, E.; Gutiérrez-Puebla, E.; Marin, J. M.; Monge, A.; Paneque, M.; Poveda, M. L.; Ruiz, C. Synthesis and X-Ray Structure of the Nickelabenzocyclopentene Complex [cyclic](Me3P)2Ni(CH2CMe2-o-C6H4). Reactivity Toward Simple, Unsaturated Molecules and the Crystal and Molecular Structure of the Cyclic Carboxylate (Me3P)2Ni(CH2CMe2-o-C6H4C(O)O). J. Am. Chem. Soc. 1989, 111, 2883−2891. (14) (a) Cámpora, J.; Llebaría, A.; Moretó, J. M.; Poveda, M. L.; Carmona, E. Reactions of the Benzonickelacyclopentene Complex [cyclic]-(Me3P)2Ni(CH2CMe2-o-C6H4) with Alkynes. Synthesis of 1,2-Dihydronaphthalenes. Organometallics 1993, 12, 4032−4038. (b) Belderrain, T. R.; Gutierrez, E.; Monge, A.; Nicasio, M. C.; Paneque, M.; Poveda, M. L.; Carmona, E. Alkylidenes by α-H Abstraction from Metallacycles. Synthesis and Characterization of Alkylidene-Bridged Complexes of Nickel. Organometallics 1993, 12, 4431−4442. (c) Cámpora, J.; Gutiérrez-Puebla, E.; Monge, A.; Palma, P.; Poveda, M. L.; Ruiz, C.; Carmona, E. Consecutive Insertion Reactions of Unsaturated Molecules into the Ni-C bonds of the Nickelacycle [cyclic]-(Me3P)2Ni(CH2CMe2-o-C6H4). Formation of Heterocycles Derived from Seven-Membered Cyclic Acid Anhydrides. Organometallics 1994, 13, 1728−1745. (15) Carmona, E.; Marín, J. M.; Palma, P.; Paneque, M.; Poveda, M. L. Pyrrolyl, Hydroxo, and Carbonate Organometallic Derivatives of Nickel(II). Crystal and Molecular Structure of [Ni(CH2C6H4-oMe)(PMe3)(μ -OH)]2·2,5-HNC4H2Me2. Inorg. Chem. 1989, 28, 1895−1900. (16) (a) Janowicz, A. H.; Bergman, R. G. C-H Activation in Completely Saturated Hydrocarbons: Direct Observation of M + R-H → M(R)(H). J. Am. Chem. Soc. 1982, 104, 352−354. (b) Hoyano, J. K.; Graham, W. A. G. Oxidative Addition of the Carbon HydrogenBonds of Neopentane and Cyclohexane to a Photochemically Generated Iridium(I) Complex. J. Am. Chem. Soc. 1982, 104, 3723−3725. (17) (a) Gutiérrez-Puebla, E.; Monge, Á .; Nicasio, M. C.; Pérez, P. J.; Poveda, M. L.; Carmona, E. C-H Bond Activation of Benzene and Cyclic Ethers by TpIr(III) species. Chem. - Eur. J. 1998, 4, 2225− 2236. (b) Slugovc, C.; Mereiter, K.; Trofimenko, S.; Carmona, E. Generation of Heteroatom-Substituted Carbene Complexes of Iridium by Double C-H Activation of Ether and Amine Substrates. Angew. Chem., Int. Ed. 2000, 39, 2158−2160. (c) Paneque, M.; Poveda, M. L.; Salazar, V.; Taboada, S.; Carmona, E.; GutiérrezPuebla, E.; Monge, A.; Ruiz, C. C-H Bond Activation of Thiophenes by Ir Complexes of the Hydrotris(3,5-dimethylpyrazolyl)borate Ligand, TpMe2. Organometallics 1999, 18, 139−149. (18) (a) Paneque, M.; Poveda, M. L.; Santos, L. L.; Carmona, E.; Lledós, A.; Ujaque, G.; Mereiter, K. A Measurable Equilibrium Between Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers. Angew. Chem., Int. Ed. 2004, 43, 3708−3711. (b) Lara, P.; Paneque, M.; Poveda, M. L.; Salazar, V.; Santos, L. L.; Carmona, E. Formation and Cleavage of C-H, C-C and C-O Bonds of OrthoMethyl-Substituted Anisoles by Late Transition Metals. J. Am. Chem. Soc. 2006, 128, 3512−3513. (c) Á lvarez, E.; Paneque, M.; Petronilho, A. G.; Poveda, M. L.; Santos, L. L.; Carmona, E.; Mereiter, K. Activation of Aliphatic Ethers by TpMe2Ir Compounds: Multiple C-H Bond Activation and C-C Bond Formation. Organometallics 2007, 26, 1231−1240. (19) (a) Parry, J.; Carmona, E.; Coles, S.; Hursthouse, M. Synthesis and Single Crystal X-Ray Diffraction Study on the First Isolable Carbonyl Complex of an Actinide, (C5Me4H)3U(CO). J. Am. Chem. Soc. 1995, 117, 2649−2650. (b) Conejo, M. M.; Parry, J. S.; Carmona, E.; Schultz, M.; Brennann, J. G.; Beshouri, S. M.; Andersen, R. A.; Rogers, R. D.; Coles, S.; Hursthouse, M. B. Carbon Monoxide and Isocyanide Complexes of Trivalent Uranium Metallocenes. Chem. - Eur. J. 1999, 5, 3000−3009. (20) Fernández, R.; Carmona, E. Recent Developments in the Chemistry of Beryllocenes. Eur. J. Inorg. Chem. 2005, 2005, 3197− 3206. 3383

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(21) (a) Conejo, M. M.; Fernández, R.; Gutiérrez-Puebla, E.; Monge, A.; Ruiz, C.; Carmona, E. Synthesis and X-Ray Structures of [Be(C5Me4H)2] and [Be(C5Me5)2]. Angew. Chem., Int. Ed. 2000, 39, 1949−1951. (b) Conejo, M. M.; Fernández, R.; del Río, D.; Carmona, E.; Monge, A.; Ruiz, C.; Márquez, A. M.; Sanz, J. F. Synthesis, SolidState Structure, and Bonding Analysis of the Beryllocenes [Be(C5Me4H)2], [Be(C5Me5)2] and [Be(C5Me5)(C5Me4H)]. Chem. Eur. J. 2003, 9, 4452−4461. (22) Fernández, R.; Resa, I.; del Río, D.; Carmona, E.; GutiérrezPuebla, E.; Monge, A. Synthesis and Solid-State Structure of Zn(η5C5Me4SiMe3)(η1-C5Me4SiMe3), a Zincocene with Nonparallel Cyclopentadienyl Rings. Organometallics 2003, 22, 381−383. (23) Resa, I.; Carmona, E.; Gutiérrez-Puebla, E.; Monge, A. Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond. Science 2004, 305, 1136−1138. (24) Carmona, E.; Galindo, E. Direct Bonds Between Metal Atoms: Zn, Cd and Hg Compounds with Metal-Metal Bonds. Angew. Chem., Int. Ed. 2008, 47, 6526−6536. (25) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P. Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers. Science 2005, 310, 844−847. (26) Carrasco, M.; Curado, N.; Maya, C.; Peloso, R.; Rodríguez, A.; Ruiz, E.; Á lvarez, S.; Carmona, E. Interconversion of Quadruply and Quintuply Bonded Molybdenum Complexes by Reductive Elimination and Oxidative Addition of Dihydrogen. Angew. Chem., Int. Ed. 2013, 52, 3227−3231.

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DOI: 10.1021/acs.organomet.8b00643 Organometallics 2018, 37, 3379−3384