Robert Crabtree | |
---|---|
Born | Robert Howard Crabtree 17 April 1948 London, England, UK |
Nationality | British/United States |
Education | Brighton College |
Alma mater | University of Oxford (BA) University of Sussex (PhD) |
Known for | Crabtree's catalyst |
Awards | Corday-Morgan Prize (1982) Centenary Prize (2013) |
Scientific career | |
Fields | Organometallic chemistry |
Institutions | Yale University Institut de Chimie des Substances Naturelles |
Thesis | Transition Metal Dinitrogen Complexes Adduct Formation and Base Character (1973) |
Doctoral advisor | Joseph Chatt |
Other academic advisors | Malcolm Green Hugh Felkin [1] |
Website | chem |
Robert Howard Crabtree FRS [2] (born 17 April 1948) is a British-American chemist. He is serving as Conkey P. Whitehead Professor Emeritus of Chemistry at Yale University in the United States. He is a naturalized citizen of the United States. [3] Crabtree is particularly known for his work on "Crabtree's catalyst" for hydrogenations, and his textbook on organometallic chemistry. [4]
Robert Howard Crabtree studied at Brighton College (1959–1966), and earned a Bachelor of Arts degree from the University of Oxford where he was a student at New College, Oxford in 1970, studying under Malcolm Green. He received his PhD from the University of Sussex in 1973, supervised by Joseph Chatt. [5]
After his PhD, he was a postdoctoral researcher with Hugh Felkin at the Institut de Chimie des Substances Naturelles at Gif-sur-Yvette, near Paris. He was a postdoctoral fellow (1973–1975) and then attaché de recherche (1975–1977). At the end of that time he was chargé de recherche. In 1977 Crabtree took an assistant professorship in Inorganic Chemistry at Yale University. He served as associate professor from 1982 to 1985, and as full professor from 1985 to 2021. [6] In retirement, he now serves as an emeritus professor of chemistry. [7]
Robert Crabtree is renowned for his influential work on hydrogenation, particularly his contributions to the development of the Crabtree catalyst. [10] This catalyst, utilizing iridium as the active metal, displays exceptional efficiency, regio- and stereoselectivity in hydrogenation reactions. Notably, when terpinen-4-ol undergoes hydrogenation, the Crabtree catalyst exhibits a remarkable preference of 1000:1 for adding hydrogen to the substrate face containing the OH group. In contrast, the hydrogenation reaction with Palladium on carbon only achieves a selectivity ratio of 20:80. The chelation of the alcohol to the catalyst is evident from the identification of a catalyst-substrate complex involving norbornene-2-ol. [11] [12]
During his early research, Crabtree also focused on C–H bond activation. [13] Crabtree's groundbreaking contribution in this area was reversing the hydrogenation reactions he developed before, particularly in stoichiometric alkane dehydrogenation. He utilized tert-butylethylene as a hydrogen acceptor to facilitate the release of hydrogen during the dehydrogenation of cyclooctane, forming bound cyclooctadiene. This discovery demonstrated one of the earliest instances of intermolecular C–H activation using a homogeneous metal complex. This achievement played a significant role in his tenure award and academic success
Another part of Crabtree's research centers on a novel form of hydrogen bonding that involves metal hydrides, resulting in unconventional bonding interactions. [14] [15] Traditional hydrogen bonds feature a protic hydrogen donor and an electronegative acceptor, while Crabtree's discoveries include aromatic ring π electrons as weaker acceptors in X–H···π hydrogen bonds (X = N, O). Surprisingly, Crabtree also observed Y–H σ bonds (Y= B or metal) acting as acceptors, leading to X–H···H–Y structures with significantly shorter H···H distances compared to typical contacts. Known as "dihydrogen bonds," these interactions exhibit bond lengths of approximately 1.8 Å, in contrast to the regular H···H length of 2.4 Å. Crabtree's findings shed light on the diverse nature of hydrogen bonding, with implications for understanding molecular structures and designing catalysts with tailored properties.
Crabtree has made significant contributions to the field of carbene chemistry, particularly in the exploration of mesoionic carbenes (MICs), or so called "abnormal carbenes". These carbenes, offer advantages as ligand systems in organometallic complexes and catalytic applications. Unlike C2 coordinated imidazolylidenes, mesoionic carbenes possess only charge-separated electronic resonance structures, allowing for greater adaptability to metal centers within catalytic cycles. Crabtree has developed novel methods for generating and isolating abnormal carbenes, providing insights into their structures and stability under different conditions. Notably, he introduced the first example of an abnormal carbene complex incorporating an iridium complex with a C4 coordinated imidazolylidene, which found application in transfer hydrogenation catalysis. [16]
Crabtree's research has made significant advancements in our understanding of O–O bond formation within manganese di-μ-oxo dimers involved in oxygen evolution. [17] [18] Through his investigations, he has put forward a simplified proposal for the reaction mechanism responsible for the generation of oxygen through the reaction of a manganese di-μ-oxo dimer with NaClO. The oxidation of the IV/IV dimer results in the production of a Mn(V)=O dimer. Subsequently, the formation of the O–O bond could potentially occur through a nucleophilic attack of OH– on the oxo group. Oxygen-18 isotope labeling experiments have demonstrated that the oxygen atoms in the evolved molecular oxygen originate from water. This system thus serves as a functional model for photosynthetic water oxidation.
Crabtree has made significant contributions in C–H bond activation, water oxidation, and hydrogenation. His approach entails selecting unique projects, conducting early critical experiments, transitioning between problems, developing air-stable catalysts, and educating through his writing.
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide, cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term "metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are representative members of this class. The field of organometallic chemistry combines aspects of traditional inorganic and organic chemistry.
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At its simplest, it's a useful way of converting alkanes, which are relatively inert and thus low-valued, to olefins, which are reactive and thus more valuable. Alkenes are precursors to aldehydes, alcohols, polymers, and aromatics. As a problematic reaction, the fouling and inactivation of many catalysts arises via coking, which is the dehydrogenative polymerization of organic substrates.
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is R−:C−R' or R=C: where the R represents substituents or hydrogen atoms.
In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst a in solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid-gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts.
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A transition metal carbene complex is an organometallic compound featuring a divalent organic ligand. The divalent organic ligand coordinated to the metal center is called a carbene. Carbene complexes for almost all transition metals have been reported. Many methods for synthesizing them and reactions utilizing them have been reported. The term carbene ligand is a formalism since many are not derived from carbenes and almost none exhibit the reactivity characteristic of carbenes. Described often as M=CR2, they represent a class of organic ligands intermediate between alkyls (−CR3) and carbynes (≡CR). They feature in some catalytic reactions, especially alkene metathesis, and are of value in the preparation of some fine chemicals.
Organoiridium chemistry is the chemistry of organometallic compounds containing an iridium-carbon chemical bond. Organoiridium compounds are relevant to many important processes including olefin hydrogenation and the industrial synthesis of acetic acid. They are also of great academic interest because of the diversity of the reactions and their relevance to the synthesis of fine chemicals.
Germylenes are a class of germanium(II) compounds with the general formula :GeR2. They are heavier carbene analogs. However, unlike carbenes, whose ground state can be either singlet or triplet depending on the substituents, germylenes have exclusively a singlet ground state. Unprotected carbene analogs, including germylenes, has a dimerization nature. Free germylenes can be isolated under the stabilization of steric hindrance or electron donation. The synthesis of first stable free dialkyl germylene was reported by Jutzi, et al in 1991.
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