Metal-ligand cooperativity

Last updated

Metal-ligand cooperativity (MLC) is a mode of reactivity in which a metal and ligand of a complex are both involved in the bond breaking or bond formation of a substrate during the course of a reaction. This ligand is an actor ligand rather than a spectator, and the reaction is generally only deemed to contain MLC if the actor ligand is doing more than leaving to provide an open coordination site. MLC is also referred to as "metal-ligand bifunctional catalysis." Note that MLC is not to be confused with cooperative binding.

Contents

The earliest reported metal-ligand cooperativity was from the Fujiwara group in the 1950s, in which they reported formation of stilbene from styrene and arenes using a palladium chloride catalyst. [1] Shvo's catalyst was developed for one of the earliest uses of ketone hydrogenation by an outer-sphere mechanism. [2] Noyori has developed many chiral catalysts for asymmetric hydrogenation. [3] Transfer hydrogenation, one of the most commonly used applications of MLC, is employed broadly in industry for large scale Noyori-type reductions. [4] [5] [6] [7]

Modes of Metal-Ligand Cooperativity

There are a variety of modes in which this cooperativity has been demonstrated. Four primary modes are generally accepted under MLC: the ligand can (1) act with Lewis acidity, (2) act with Lewis basicity, (3) play a role in aromatization and dearomatization, or (4) be redox non-innocent. [8]

The ligand can act as a Lewis acid and accept electrons from an incoming substrate as it binds to the metal, as in employed in dehydrogenation catalysis. Conversely, the ligand can be Lewis basic and bind the substrate; this Lewis basicity is most frequently seen in hydrogenation catalysis.

The aromatization and dearomatization of a ligand can serve to facilitate a reaction. As shown in the figure, a ligand can be dearomatized by a base and thus activated toward cleaving a C-H or H-H bond and be subsequently rearomatized during substrate bond cleavage. NHC ligands and other pincer ligands are frequently employed in this mode of MLC. [9] In some reports, with bidentate ligands, ligand dearomatization is not observed when the complex is treated with base but rather a complex with a formal metal-carbon bond is observed (that then acts as a Lewis basic ligand). [10] [11]

The ligand can also be redox non-innocent to facilitate reactions that the metal would otherwise be unable to activate. [8] The ligand can act as an electron reservoir, which is enabled when ligands contain frontier orbitals of suitable energy to participate in the redox event themselves, and can accept or donate electrons during the course of the reaction, allowing the metal to modulate its oxidation state. This allows metals which normally only participate in one electron regimes to be used in two electron regimes with a redox non-innocent ligand to store electrons during the reaction. Dithiolate ligands have been used extensively as one electron redox active ligands in metal complexes. [12] For example, dithiolates have been demonstrated to allow for the selective and reversible reduction of ethylene in the presence H2, CO, and H2S. This has applications in the purification of ethylene gas streams, in which ethylene can be reduced electrochemically by a dithiolate, selectively removed from the impurities in the stream, and then reversibly desaturated. [13]

Electrochemical metal-ligand cooperativity in redox reactions allows for ease of tuning the potential of the ligands to avoid off-target reactivity. [14]

Modes of metal ligand cooperativity where X-H and X-S are some substrates. Modes of Metal Ligand Cooperativity.png
Modes of metal ligand cooperativity where X-H and X-S are some substrates.

There are a number of other ligand modes of reactivity which are sometimes classified under MLC. This includes reactions in which the ligand accepts or loses a proton, though not directly from or to the substrate. [15] Ligands can also be used to form stabilizing H-bonds, which can be applied in molecular recognition catalysis. [15] Ligands can also be designed to be photoresponsive, with applications in molecular switches. [15] Ligands may also be considered to be involved in MLC while acting only in the second coordination sphere (not directly bound to the metal) but acting as a proton shuttle. [16] Frustrated Lewis pairs, in which an ion pair of the type [R3B-H]−[H-Ar3]+ transfer a hydride and proton are also sometimes classified under MLC. [16]

Mechanism of Hydrogenations with Metal-Ligand Cooperativity

MLC is most frequently used in hydrogenations, with many applications in asymmetric catalysis and in process scale production of chemicals. In a hydrogenation, there is a transfer of a hydride and a hydrogen to a substrate. Typical substrates include aldehydes, ketones, and imines. As this is a common use for MLC, it is instructive in understanding the mechanism of metal-ligand cooperativity. MLC occurs through an outer sphere mechanism. An outer sphere mechanism does not necessitate that the metal undergo oxidative addition or reductive elimination. Thus, H2 is not added across the metal, but rather across the metal and a ligand; alternatively, the metal complexes are preformed to contain a hydride ligand as well as a ligand with a hydrogen alpha to the metal. Thus, the hydride and hydrogen are adjacent to one another, facilitating the transfer to the substrate; this transfer occurs without the substrate ever binding to the metal itself. [17] Though amine is by far the most used ligand in cooperativity, other actor ligands include alkoxides and thiols.

The outer sphere mechanism for MLC compared to an inner sphere mechanism without ligand cooperativity. Inner Vs Outer Sphere Mechanisms.png
The outer sphere mechanism for MLC compared to an inner sphere mechanism without ligand cooperativity.

In contrast, in an inner sphere mechanism, the substrate will be inserted into the metal and reaction with hydrogen will then afford the hydrogenated product. This mechanism does not employ MLC. The differentiation between an outer sphere mechanism relying on MLC and an inner sphere mechanism is exemplified by cobalt hydrogenation with an amine pincer ligand. [8] In the outer sphere mechanism, the hydrogen on the pincer ligand is added into the ketone along with a hydride ligand on the metal. [18] It is worth noting that there is debate over the concertedness of the transition state of this outer sphere hydrogenation step, and different reactions and catalysts may be either concerted or stepwise, and in some scenarios there may be multiple pathways at play. [5] In comparison to the ketone hydrogenation, an olefin undergoes an inner sphere mechanism under the same reaction conditions, in which the olefin inserts directly into the metal. These mechanistic differences between the ketone and olefin are corroborated by the observation that the ketone hydrogenation will not occur with an N-Me pincer ligand, and the olefin hydrogenation will proceed with the N-Me ligand, suggesting the ketone requires the presence of the N-H bond while the olefin does not. [18]

Common Ligands

Ruthenium diphosphine diamine complex Ruthenium diamine diphosphine ligand.jpg
Ruthenium diphosphine diamine complex

MLC is most broadly used with M-NH systems. Nyori and others have developed an extensive library of diamine ligands which serve in hydrogenation reactions, following the general outer sphere mechanism illustrated above. These systems are typically ruthenium complexes containing phosphine ligands as the spectator ligands. [19] [20] Many of these diphosphine ligands, such as BINAP, contain arene rings and impart chirality from atropisomerism; the rigidity of the phosphene ligands can impart chirality on prochiral substrates with high fidelity, allowing for asymmetric hydrogenation. Reactivity of metal complexes used in MLC can be tuned greatly by the use of different diphosphine spectator ligands.

Shvo's catalyst and its dissociated state, in which the 18e- complex (2) is the active form Shvo's catalyst.jpg
Shvo’s catalyst and its dissociated state, in which the 18e- complex (2) is the active form

M-OH metal ligand systems have application in MLC. Shvo's catalyst was one of the earliest complexes developed for ketone and aldehyde reductions to alcohols. The ruthenium complex (1), upon heating, dissociates into a 18 electron complex (2) and a 16 electron complex (3), the former of which is catalytically active. [21] The hydroxy group on the cyclopentadienyl is the actor ligand, donating a hydrogen in an outer sphere mechanism. Bäckvall has developed use for Shvo's catalyst in the dynamic kinetic resolution of alcohols with lipases. [22]

Bergman and coworkers developed a sulfur ligand for activation of H-H as well as Si-H bonds. [23] [24] A titanium sulfide complex binds H2 across the titanium and sulfur, yielding a hydride and thiol ligand. A similar mode of reactivity is seen with H-Si bonds, in which the sulfide forms a bond with the silicon, and the titanium accepts the hydride. The use of sulfur ligands in MHC has continued to expand since Bergman's early work in the field. Iridium and rhenium complexes with bridging sulfides have been demonstrated to heterolytically cleave H2. [25] [26]

Metal boron complexes have also been demonstrated to be useful in activating H2. [27] [28] [29] [30] These ligands are less developed for the purpose of MLC, and commonly suffer from off target alkyl and aryl migration from the boron ligand to other ligands or substrates which disrupts the catalytic cycle [9]

Related Research Articles

<span class="mw-page-title-main">Hydrogenation</span> Chemical reaction between molecular hydrogen and another compound or element

Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons.

In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6×106 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and pharmaceuticals. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.

<span class="mw-page-title-main">Wilkinson's catalyst</span> Chemical compound

Wilkinson's catalyst (chlorido­tris(triphenylphosphine)­rhodium(I)) is a coordination complex of rhodium with the formula [RhCl(P(C6H5)3], where 'Ph' denotes a phenyl group. It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so in tetrahydrofuran or chlorinated solvents such as dichloromethane. The compound is widely used as a catalyst for hydrogenation of alkenes. It is named after chemist and Nobel laureate Sir Geoffrey Wilkinson, who first popularized its use.

<span class="mw-page-title-main">Wacker process</span> Chemical reaction

The Wacker process or the Hoechst-Wacker process refers to the oxidation of ethylene to acetaldehyde in the presence of palladium(II) chloride and copper(II) chloride as the catalyst. This chemical reaction was one of the first homogeneous catalysis with organopalladium chemistry applied on an industrial scale.

In chemistry, transfer hydrogenation is a chemical reaction involving the addition of hydrogen to a compound from a source other than molecular H2. It is applied in laboratory and industrial organic synthesis to saturate organic compounds and reduce ketones to alcohols, and imines to amines. It avoids the need for high-pressure molecular H2 used in conventional hydrogenation. Transfer hydrogenation usually occurs at mild temperature and pressure conditions using organic or organometallic catalysts, many of which are chiral, allowing efficient asymmetric synthesis. It uses hydrogen donor compounds such as formic acid, isopropanol or dihydroanthracene, dehydrogenating them to CO2, acetone, or anthracene respectively. Often, the donor molecules also function as solvents for the reaction. A large scale application of transfer hydrogenation is coal liquefaction using "donor solvents" such as tetralin.

A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. Many kinds of FLPs have been devised, and many simple substrates exhibit activation.

Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information to transfer from one molecule to the target, forming the product as a single enantiomer. The chiral information is most commonly contained in a catalyst and, in this case, the information in a single molecule of catalyst may be transferred to many substrate molecules, amplifying the amount of chiral information present. Similar processes occur in nature, where a chiral molecule like an enzyme can catalyse the introduction of a chiral centre to give a product as a single enantiomer, such as amino acids, that a cell needs to function. By imitating this process, chemists can generate many novel synthetic molecules that interact with biological systems in specific ways, leading to new pharmaceutical agents and agrochemicals. The importance of asymmetric hydrogenation in both academia and industry contributed to two of its pioneers — William Standish Knowles and Ryōji Noyori — being collectively awarded one half of the 2001 Nobel Prize in Chemistry.

<span class="mw-page-title-main">Shvo catalyst</span> Chemical compound

The Shvo catalyst is an organoruthenium compound that catalyzes the hydrogenation of polar functional groups including aldehydes, ketones and imines. The compound is of academic interest as an early example of a catalyst for transfer hydrogenation that operates by an "outer sphere mechanism". Related derivatives are known where p-tolyl replaces some of the phenyl groups. Shvo's catalyst represents a subset of homogeneous hydrogenation catalysts that involves both metal and ligand in its mechanism.

<span class="mw-page-title-main">Cobalt tetracarbonyl hydride</span> Chemical compound

Cobalt tetracarbonyl hydride is an organometallic compound with the formula HCo(CO)4. It is a volatile, yellow liquid that forms a colorless vapor and has an intolerable odor. The compound readily decomposes upon melt and in absentia of high CO partial pressures forms Co2(CO)8. Despite operational challenges associated with its handling, the compound has received considerable attention for its ability to function as a catalyst in hydroformylation. In this respect, HCo(CO)4 and related derivatives have received significant academic interest for their ability to mediate a variety of carbonylation (introduction of CO into inorganic compounds) reactions.

<span class="mw-page-title-main">Hydrogenation of carbon–nitrogen double bonds</span>

In chemistry, the hydrogenation of carbon–nitrogen double bonds is the addition of the elements of dihydrogen (H2) across a carbon–nitrogen double bond, forming amines or amine derivatives. Although a variety of general methods have been developed for the enantioselective hydrogenation of ketones, methods for the hydrogenation of carbon–nitrogen double bonds are less general. Hydrogenation of imines is complicated by both syn/anti isomerization and tautomerization to enamines, which may be hydrogenated with low enantioselectivity in the presence of a chiral catalyst. Additionally, the substituent attached to nitrogen affects both the reactivity and spatial properties of the imine, complicating the development of a general catalyst system for imine hydrogenation. Despite these challenges, methods have been developed that address particular substrate classes, such as N-aryl, N-alkyl, and endocyclic imines.

<span class="mw-page-title-main">Boranylium ions</span>

In chemistry, a boranylium ion is an inorganic cation with the chemical formula BR+
2, where R represents a non-specific substituent. Being electron-deficient, boranylium ions form adducts with Lewis bases. Boranylium ions have historical names that depend on the number of coordinated ligands:

<span class="mw-page-title-main">Copper hydride</span> Chemical compound

Copper hydride is an inorganic compound with the chemical formula CuHn where n ~ 0.95. It is a red solid, rarely isolated as a pure composition, that decomposes to the elements. Copper hydride is mainly produced as a reducing agent in organic synthesis and as a precursor to various catalysts.

In organic chemistry, the Fujiwara–Moritani reaction is a type of cross coupling reaction where an aromatic C-H bond is directly coupled to an olefinic C-H bond, generating a new C-C bond. This reaction is performed in the presence of a transition metal, typically palladium. The reaction was discovered by Yuzo Fujiwara and Ichiro Moritani in 1967. An external oxidant is required to this reaction to be run catalytically. Thus, this reaction can be classified as a C-H activation reaction, an oxidative Heck reaction, and a C-H olefination. Surprisingly, the Fujiwara–Moritani reaction was discovered before the Heck reaction.

The Mukaiyama hydration is an organic reaction involving formal addition of an equivalent of water across an olefin by the action of catalytic bis(acetylacetonato)cobalt(II) complex, phenylsilane and atmospheric oxygen to produce an alcohol with Markovnikov selectivity.

In organic chemistry, the Murai reaction is an organic reaction that uses C-H activation to create a new C-C bond between a terminal or strained internal alkene and an aromatic compound using a ruthenium catalyst. The reaction, named after Shinji Murai, was first reported in 1993. While not the first example of C-H activation, the Murai reaction is notable for its high efficiency and scope. Previous examples of such hydroarylations required more forcing conditions and narrow scope.

Germanium(II) hydrides, also called germylene hydrides, are a class of Group 14 compounds consisting of low-valent germanium and a terminal hydride. They are also typically stabilized by an electron donor-acceptor interaction between the germanium atom and a large, bulky ligand.

In homogeneous catalysis C2-symmetric ligands refer to ligands that lack mirror symmetry but have C2 symmetry. Such ligands are usually bidentate and are valuable in catalysis. The C2 symmetry of ligands limits the number of possible reaction pathways and thereby increases enantioselectivity, relative to asymmetrical analogues. C2-symmetric ligands are a subset of chiral ligands. Chiral ligands, including C2-symmetric ligands, combine with metals or other groups to form chiral catalysts. These catalysts engage in enantioselective chemical synthesis, in which chirality in the catalyst yields chirality in the reaction product.

<span class="mw-page-title-main">Lanthanocene</span>

A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.

Heterobimetallic catalysis is an approach to catalysis that employs two different metals to promote a chemical reaction. Included in this definition are cases where: 1) each metal activates a different substrate, 2) both metals interact with the same substrate, and 3) only one metal directly interacts with the substrate(s), while the second metal interacts with the first.

β-Carbon elimination is a type of reaction in organometallic chemistry wherein an allyl ligand bonded to a metal center is broken into the corresponding metal-bonded alkyl (aryl) ligand and an alkene. It is a subgroup of elimination reactions. Though less common and less understood than β-hydride elimination, it is an important step involved in some olefin polymerization processes and transition-metal-catalyzed organic reactions.

References

  1. ↑ Moritanl, Ichiro; Fujiwara, Yuzo (1967-01-01). "Aromatic substitution of styrene-palladium chloride complex". Tetrahedron Letters. 8 (12): 1119–1122. doi:10.1016/S0040-4039(00)90648-8. ISSN   0040-4039.
  2. ↑ Hartwig, John F. (2010). Organotransition metal chemistry : from bonding to catalysis. Mill Valley, Calif. ISBN   978-1-891389-53-5. OCLC   310401036.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ↑ Ohkuma, Takeshi; Ooka, Hirohito; Hashiguchi, Shohei; Ikariya, Takao; Noyori, Ryoji (1995-03-01). "Practical Enantioselective Hydrogenation of Aromatic Ketones". Journal of the American Chemical Society. 117 (9): 2675–2676. doi:10.1021/ja00114a043. ISSN   0002-7863.
  4. ↑ Crabtree, Robert H. (2014). The organometallic chemistry of the transition metals (Sixth ed.). Hoboken, New Jersey. ISBN   978-1-118-78824-0. OCLC   863383849.{{cite book}}: CS1 maint: location missing publisher (link)
  5. 1 2 Dub, Pavel A.; Gordon, John C. (2017-10-06). "Metal–Ligand Bifunctional Catalysis: The "Accepted" Mechanism, the Issue of Concertedness, and the Function of the Ligand in Catalytic Cycles Involving Hydrogen Atoms". ACS Catalysis. 7 (10): 6635–6655. doi:10.1021/acscatal.7b01791. OSTI   1409775.
  6. ↑ Zhang, Xumu; Shao, Pan-Lin (2021), "Industrial Applications of Asymmetric (Transfer) Hydrogenation", Asymmetric Hydrogenation and Transfer Hydrogenation, John Wiley & Sons, Ltd, pp. 175–219, doi:10.1002/9783527822294.ch6, ISBN   978-3-527-82229-4, S2CID   233588784 , retrieved 2021-05-17
  7. ↑ Shimizu, Hideo; Nagasaki, Izuru; Matsumura, Kazuhiko; Sayo, Noboru; Saito, Takao (2007-12-01). "Developments in Asymmetric Hydrogenation from an Industrial Perspective". Accounts of Chemical Research. 40 (12): 1385–1393. doi:10.1021/ar700101x. ISSN   0001-4842. PMID   17685581.
  8. 1 2 3 Elsby, Matthew R.; Baker, R. Tom (2020). "Strategies and mechanisms of metal–ligand cooperativity in first-row transition metal complex catalysts". Chemical Society Reviews. 49 (24): 8933–8987. doi:10.1039/D0CS00509F. ISSN   0306-0012. PMID   33164012. S2CID   226284136.
  9. 1 2 Khusnutdinova, Julia R.; Milstein, David (2015). "Metal–Ligand Cooperation". Angewandte Chemie International Edition. 54 (42): 12236–12273. doi:10.1002/anie.201503873. ISSN   1521-3773. PMID   26436516.
  10. ↑ Vigneswaran, Vipulan; Abhyankar, Preshit C.; MacMillan, Samantha N.; Lacy, David C. (2022-01-10). "H 2 Activation across Manganese(I)–C Bonds: Atypical Metal–Ligand Cooperativity in the Aromatization/Dearomatization Paradigm". Organometallics. 41 (1): 67–75. doi:10.1021/acs.organomet.1c00606. ISSN   0276-7333. S2CID   245571634.
  11. ↑ Fanara, Paul M.; Vigneswaran, Vipulan; Gunasekera, Parami S.; MacMillan, Samantha N.; Lacy, David C. (2022-01-10). "Reversible Photoisomerization in a Ru cis -Dihydride Catalyst Accessed through Atypical Metal–Ligand Cooperative H 2 Activation: Photoenhanced Acceptorless Alcohol Dehydrogenation". Organometallics. 41 (1): 93–98. doi:10.1021/acs.organomet.1c00648. ISSN   0276-7333. S2CID   245315751.
  12. ↑ Eisenberg, Richard; Gray, Harry B. (2011-10-17). "Noninnocence in Metal Complexes: A Dithiolene Dawn". Inorganic Chemistry. 50 (20): 9741–9751. doi:10.1021/ic2011748. ISSN   0020-1669. PMID   21913669.
  13. ↑ Wang, K. (2001-01-05). "Toward Separation and Purification of Olefins Using Dithiolene Complexes: An Electrochemical Approach". Science. 291 (5501): 106–109. Bibcode:2001Sci...291..106W. doi:10.1126/science.291.5501.106. PMID   11141557.
  14. ↑ Derrick, Jeffrey S.; Loipersberger, Matthias; Chatterjee, Ruchira; Iovan, Diana A.; Smith, Peter T.; Chakarawet, Khetpakorn; Yano, Junko; Long, Jeffrey R.; Head-Gordon, Martin; Chang, Christopher J. (2020-12-02). "Metal–Ligand Cooperativity via Exchange Coupling Promotes Iron- Catalyzed Electrochemical CO2 Reduction at Low Overpotentials". Journal of the American Chemical Society. 142 (48): 20489–20501. doi:10.1021/jacs.0c10664. ISSN   0002-7863. OSTI   1844513. PMID   33207117. S2CID   227067774.
  15. 1 2 3 Crabtree, Robert H. (2011). "Multifunctional ligands in transition metal catalysis". New J. Chem. 35 (1): 18–23. doi:10.1039/C0NJ00776E. ISSN   1144-0546.
  16. 1 2 Annibale, Vincent T.; Song, Datong (2013-07-01). "Multidentate actor ligands as versatile platforms for small molecule activation and catalysis". RSC Advances. 3 (29): 11432–11449. Bibcode:2013RSCAd...311432A. doi:10.1039/C3RA40618K. ISSN   2046-2069.
  17. ↑ Eisenstein, Odile; Crabtree, Robert H. (2013). "Outer sphere hydrogenation catalysis". New J. Chem. 37 (1): 21–27. doi:10.1039/C2NJ40659D. ISSN   1144-0546.
  18. 1 2 Zhang, Guoqi; Vasudevan, Kalyan V.; Scott, Brian L.; Hanson, Susan K. (2013-06-12). "Understanding the Mechanisms of Cobalt-Catalyzed Hydrogenation and Dehydrogenation Reactions". Journal of the American Chemical Society. 135 (23): 8668–8681. doi:10.1021/ja402679a. ISSN   0002-7863. PMID   23713752.
  19. ↑ Ohkuma, Takeshi; Utsumi, Noriyuki; Tsutsumi, Kunihiko; Murata, Kunihiko; Sandoval, Christian; Noyori, Ryoji (2006-07-01). "The Hydrogenation/Transfer Hydrogenation Network: Asymmetric Hydrogenation of Ketones with Chiral η6-Arene/N-Tosylethylenediamine−Ruthenium(II) Catalysts". Journal of the American Chemical Society. 128 (27): 8724–8725. doi:10.1021/ja0620989. ISSN   0002-7863. PMID   16819854.
  20. ↑ Hashiguchi, Shohei; Fujii, Akio; Takehara, Jun; Ikariya, Takao; Noyori, Ryoji (1995-07-01). "Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed by Chiral Ruthenium(II) Complexes". Journal of the American Chemical Society. 117 (28): 7562–7563. doi:10.1021/ja00133a037. ISSN   0002-7863.
  21. ↑ Shvo, Youval.; Czarkie, Dorotha.; Rahamim, Yocheved.; Chodosh, Daniel F. (1986-11-01). "A new group of ruthenium complexes: structure and catalysis". Journal of the American Chemical Society. 108 (23): 7400–7402. doi:10.1021/ja00283a041. ISSN   0002-7863.
  22. ↑ Martín-Matute, Belén; Bäckvall, Jan-E (2007-04-01). "Dynamic kinetic resolution catalyzed by enzymes and metals". Current Opinion in Chemical Biology. 11 (2): 226–232. doi:10.1016/j.cbpa.2007.01.724. ISSN   1367-5931. PMID   17349815.
  23. ↑ Sweeney, Zachary K.; Polse, Jennifer L.; Bergman, Robert G.; Andersen, Richard A. (1999-12-01). "Dihydrogen Activation by Titanium Sulfide Complexes". Organometallics. 18 (26): 5502–5510. doi:10.1021/om9907876. ISSN   0276-7333. PMC   1444909 . PMID   16633550.
  24. ↑ Sweeney, Zachary K.; Polse, Jennifer L.; Andersen, Richard A.; Bergman, Robert G.; Kubinec, Mark G. (1997-05-01). "Synthesis, Structure, and Reactivity of Monomeric Titanocene Sulfido and Disulfide Complexes. Reaction of H2 with a Terminal MS Bond". Journal of the American Chemical Society. 119 (19): 4543–4544. doi:10.1021/ja970168t. ISSN   0002-7863.
  25. ↑ Linck, Rachel C.; Pafford, Robert J.; Rauchfuss, Thomas B. (2001-09-01). "Heterolytic and Homolytic Activation of Dihydrogen at an Unusual Iridium (II) Sulfide". Journal of the American Chemical Society. 123 (36): 8856–8857. doi:10.1021/ja010603q. ISSN   0002-7863. PMID   11535095.
  26. ↑ Ienco, Andrea; Calhorda, Maria José; Reinhold, Joachim; Reineri, Francesca; Bianchini, Claudio; Peruzzini, Maurizio; Vizza, Francesco; Mealli, Carlo (2004-09-01). "Activation of Molecular Hydrogen over a Binuclear Complex with Rh2S2 Core: DFT Calculations and NMR Mechanistic Studies". Journal of the American Chemical Society. 126 (38): 11954–11965. doi:10.1021/ja047992j. ISSN   0002-7863. PMID   15382931.
  27. ↑ Bonanno, Jeffrey B.; Henry, Thomas P.; Wolczanski, Peter T.; Pierpont, Aaron W.; Cundari, Thomas R. (2007-02-19). "Evidence for Strong Tantalum-to-Boron Dative Interactions in (silox)3Ta(BH3) and (silox)3Ta(η2-B,Cl-BCl2Ph) (silox = tBu3SiO)1". Inorganic Chemistry. 46 (4): 1222–1232. doi:10.1021/ic0616885. ISSN   0020-1669. PMID   17249656.
  28. ↑ Tsoureas, Nikolaos; Kuo, Yu-Ying; Haddow, Mairi F.; Owen, Gareth R. (2010-12-06). "Double addition of H2 to transition metal–borane complexes: a 'hydride shuttle' process between boron and transition metal centres". Chemical Communications. 47 (1): 484–486. doi:10.1039/C0CC02245D. ISSN   1364-548X. PMID   20938529.
  29. ↑ Harman, W. Hill; Peters, Jonas C. (2012-03-21). "Reversible H2 Addition across a Nickel–Borane Unit as a Promising Strategy for Catalysis". Journal of the American Chemical Society. 134 (11): 5080–5082. doi:10.1021/ja211419t. ISSN   0002-7863. PMID   22380492.
  30. ↑ Fong, Henry; Moret, Marc-Etienne; Lee, Yunho; Peters, Jonas C. (2013-05-24). "Heterolytic H2 Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane". Organometallics. 32 (10): 3053–3062. doi:10.1021/om400281v. ISSN   0276-7333. PMC   3757927 . PMID   24000270.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.