Thiol is an organosulfur compound of the form R-SH, where R represents an alkyl or other organic substituent. Thiols are the sulfur analogue of alcohols, the word is a portmanteau of "thion" + "alcohol," with the first word deriving from Greek θεῖον = "sulfur"; the -- SH functional group itself is referred to as either a sulfhydryl group. Many thiols have strong odors resembling that of rotten eggs. Thiols are used as odorants to assist in the detection of natural gas, the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans; the term "mercaptan" was introduced in 1832 by William Christopher Zeise and is derived from the Latin mercurium captāns because the thiolate group bonds strongly with mercury compounds. Thiols and alcohols have similar connectivity; because sulfur is a larger element than oxygen, the C–S bond lengths – around 180 picometres in length – is about 40 picometers longer than a typical C–O bond. The C -- S -- H angles approach 90 °.
In the solid or liquids, the hydrogen-bonding between individual thiol groups is weak, the main cohesive force being van der Waals interactions between the polarizable divalent sulfur centers. The S-H bond is much weaker than the O-H bond as reflected in their respective bond dissociation energy. For CH3S-H, the BDE is 366 kJ/mol. Due to the small difference in the electronegativity of sulfur and hydrogen, an S–H bond is polar. In contrast, O-H bonds in hydroxyl groups are more polar. Thiols have a lower dipole moment relative to the corresponding alcohol. There are several ways to name the alkylthiols: The suffix -thiol is added to the name of the alkane; this method is nearly identical to naming an alcohol and is used by the IUPAC, e.g. CH3SH would be methanethiol; the word mercaptan replaces alcohol in the name of the equivalent alcohol compound. Example: CH3SH would be methyl mercaptan, just as CH3OH is called methyl alcohol; the term sulfanyl or mercapto is used as e.g. mercaptopurine. Many thiols have strong odors resembling that of garlic.
The odors of thiols those of low molecular weight, are strong and repulsive. The spray of skunks consists of low-molecular-weight thiols and derivatives; these compounds are detectable by the human nose at concentrations of only 10 parts per billion. Human sweat contains /-3-methyl-3-sulfanylhexan-1-ol, detectable at 2 parts per billion and having a fruity, onion-like odor. Methanethiol is a strong-smelling volatile thiol detectable at parts per billion levels, found in male mouse urine. Lawrence C. Katz and co-workers showed that MTMT functioned as a semiochemical, activating certain mouse olfactory sensory neurons, attracting female mice. Copper has been shown to be required by a specific mouse olfactory receptor, MOR244-3, responsive to MTMT as well as to various other thiols and related compounds. A human olfactory receptor, OR2T11, has been identified which, in the presence of copper, is responsive to the gas odorants ethanethiol and t-butyl mercaptan as well as other low molecular weight thiols, including allyl mercaptan found in human garlic breath, the strong-smelling cyclic sulfide thietane.
Thiols are responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the "skunky" odor of beer, exposed to ultraviolet light. Not all thiols have unpleasant odors. For example, furan-2-ylmethanethiol contributes to the aroma of roasted coffee, whereas grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit; the effect of the latter compound is present only at low concentrations. The pure mercaptan has an unpleasant odor. Natural gas distributors were required to add thiols ethanethiol, to natural gas after the deadly New London School explosion in New London, Texas, in 1937. Many gas distributors were odorizing gas prior to this event. Most gas odorants utilized contain mixtures of mercaptans and sulfides, with t-butyl mercaptan as the main odor constituent in natural gas and ethanethiol in liquefied petroleum gas. In situations where thiols are used in commercial industry, such as liquid petroleum gas tankers and bulk handling systems, an oxidizing catalyst is used to destroy the odor.
A copper-based oxidation catalyst neutralizes the volatile thiols and transforms them into inert products. Thiols show little association both with water molecules and among themselves. Hence, they have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight. For this reason thiols and corresponding thioether functional group isomers have similar solubility characteristics and boiling points, whereas the same is not true of alcohols and their corresponding isomeric ethers; the S-H bond in thiols is weak compared to the O-H bond in alcohols. For CH3X-H, the bond enthalpies are 365.07 for X = S and 440.2 kcal/mol for X = O. H-atom abstraction from a thiol gives a thiyl radical with the formula RS. where R = alkyl or aryl. Volatile thiols are and unerringly detected by their distinctive odor. S-specific analyzers for gas chromatographs are useful. Spectroscopic indicators are the D2O-exchangeable SH signal in the 1H NMR spectrum; the νSH band appears near 2400 cm−
Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, not consumed in the catalyzed reaction and can continue to act repeatedly. Because of this, only small amounts of catalyst are required to alter the reaction rate in principle. In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst reacts to form a temporary intermediate, which regenerates the original catalyst in a cyclic process. A substance which provides a mechanism with a higher activation energy does not decrease the rate because the reaction can still occur by the non-catalyzed route. An added substance which does reduce the reaction rate is not considered a catalyst but a reaction inhibitor. Catalysts may be classified as either heterogeneous. A homogeneous catalyst is one whose molecules are dispersed in the same phase as the reactant's molecules.
A heterogeneous catalyst is one whose molecules are not in the same phase as the reactant's, which are gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are considered as a third category. In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations; the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have a lower activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature and for the same reactant concentrations. However, the detailed mechanics of catalysis is complex. Catalysts may bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to reactive forms, such as chemisorbed hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions are typical chemical reactions. The catalyst participates in this slowest step, rates are limited by amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or sublimate in a solid–gas system; the production of most industrially important chemicals involves catalysis. Most biochemically significant processes are catalysed.
Research into catalysis is a major field in applied science and involves many areas of chemistry, notably organometallic chemistry and materials science. Catalysis is relevant to many aspects of environmental science, e.g. the catalytic converter in automobiles and the dynamics of the ozone hole. Catalytic reactions are preferred in environmentally friendly green chemistry due to the reduced amount of waste generated, as opposed to stoichiometric reactions in which all reactants are consumed and more side products are formed. Many transition metals and transition metal complexes are used in catalysis as well. Catalysts called. A catalyst works by providing an alternative reaction pathway to the reaction product; the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates oxygen, as shown below. 2 H2O2 → 2 H2O + O2This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow.
In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available. This reaction is affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms. Upon the addition of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly; this effect is seen by the effervescence of oxygen. The manganese dioxide is not consumed in the reaction, thus may be recovered unchanged, re-used indefinitely. Accordingly, manganese dioxide catalyses this reaction. Catalytic activity is denoted by the symbol z and measured in mol/s, a unit, called katal and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the catalyst under certain conditions, in relation to a specific chemical reaction. Catalytic activity of one katal of a catalyst means one mole of that catalyst will catalyse 1 mole of the reactant to product in one second. A catalyst may and will have different catalytic activity for di
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as RO −. Alkoxides are strong bases and, when R is not good nucleophiles and good ligands. Alkoxides, although not stable in protic solvents such as water, occur as intermediates in various reactions, including the Williamson ether synthesis. Transition metal alkoxides are used for coatings and as catalysts. Enolates are unsaturated alkoxides derived by deprotonation of a C-H bond adjacent to a ketone or aldehyde; the nucleophilic center for simple alkoxides is located on the oxygen, whereas the nucleophilic site on enolates is delocalized onto both carbon and oxygen sites. Phenoxides are close relatives of the alkoxides, in which the alkyl group is replaced by a derivative of benzene. Phenol is more acidic than a typical alcohol, they are, however easier to handle, yield derivatives that are more crystalline than those of the alkoxides. Alkali metal alkoxides are oligomeric or polymeric compounds when the R group is small.
The alkoxide anion is a good bridging ligand, thus many alkoxides feature M2O or M3O linkages. In solution, the alkali metal derivatives exhibit strong ion-pairing, as expected for the alkali metal derivative of a basic anion. Alkoxides can be produced by several routes starting from an alcohol. Reducing metals react directly with alcohols to give the corresponding metal alkoxide; the alcohol serves as an acid, hydrogen is produced as a by-product. A classic case is sodium methoxide produced by the addition of sodium metal to methanol: 2 CH3OH + 2 Na → 2 CH3ONa + H2Other alkali metals can be used in place of sodium, most alcohols can be used in place of methanol. Another similar reaction occurs when an alcohol is reacted with a metal hydride such as NaH; the metal hydride removes the hydrogen atom from the hydroxyl group and forms a negatively charged alkoxide ion. Titanium tetrachloride reacts with alcohols to give the corresponding tetraalkoxides, concomitant with the evolution of hydrogen chloride: TiCl4 + 4 2CHOH → Ti4 + 4 HClThe reaction can be accelerated by the addition of a base, such as a tertiary amine.
Many other metal and main group halides can be used instead of titanium, for example SiCl4, ZrCl4, PCl3. Many alkoxides are prepared by salt-forming reactions from a metal chloride and sodium alkoxide: n NaOR + MCln → Mn + n NaClSuch reactions are favored by the lattice energy of the NaCl, purification of the product alkoxide is simplified by the fact that NaCl is insoluble in common organic solvents. Many alkoxides can be prepared by anodic dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive; the metals may be etc.. The conductive additive may be quaternary ammonium halide, or other; some examples of metal alkoxides obtained by this technique: Ti4, Nb210, Ta210, 2, Re2O36, Re4O612, Re4O610. The alkoxide ion can react with a primary alkyl halide in an SN2 reaction to form a methyl ether. Metal alkoxides hydrolyse with water according to the following equation: 2 LnMOR + H2O → 2O + 2 ROHwhere R is an organic substituent and L is an unspecified ligand A well-studied case is the irreversible hydrolysis of titanium ethoxide: 1/n n + 2 H2O → TiO2 + 4 HOCH2CH3By controlling the stoichiometry and steric properties of the alkoxide, such reactions can be arrested leading to metal-oxy-alkoxides, which are oligonuclear complexes.
Other alcohols can be employed in place of water. In this way one alkoxide can be converted to another, the process is properly referred to as alcoholysis; the position of the equilibrium can be controlled by the acidity of the alcohol. More the alcoholysis can be controlled by selectively evaporating the more volatile component. In this way, ethoxides can be converted to butoxides. In the transesterification process, metal alkoxides react with esters to bring about an exchange of alkyl groups between metal alkoxide and ester. With the metal alkoxide complex in focus, the result is the same as for alcoholysis, namely the replacement of alkoxide ligands, but at the same time the alkyl groups of the ester are changed, which can be the primary goal of the reaction. Sodium methoxide, for example, is used for this purpose, a reaction, relevant to the production of "bio-diesel". Many metal alkoxide compounds feature oxo-ligands. Oxo-ligands arise via the hydrolysis accidentally, via ether elimination: 2 LnMOR → 2O + R2OAdditionally, low valent metal alkoxides are susceptible to oxidation by air Characteristically, transition metal alkoxides are polynuclear, they contain more than one metal.
Alkoxides are sterically undemanding and basic ligands that tend to bridge metals. Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed; the metal ratio in such compounds can vary over a broad range. For instance, the substitution of molybdenum and tungsten for rhenium in the complexes Re4O6−y12+y allo
A Gilman reagent is a lithium and copper reagent compound, R2CuLi, where R is an alkyl or aryl. These reagents are useful because, unlike related Grignard reagents and organolithium reagents, they react with organic halides to replace the halide group with an R group; such displacement reactions allow for the synthesis of complex products from simple building blocks. These reagents were discovered by coworkers. Lithium dimethylcopper 2CuLi can be prepared by adding copper iodide to methyllithium in tetrahydrofuran at −78 °C. In the reaction depicted below, the Gilman reagent is a methylating reagent reacting with an alkyne in a conjugate addition, the negative charge is trapped in a nucleophilic acyl substitution with the ester group forming a cyclic enone. Due to the softness of the nucleophile, they do 1,4 addition on conjugated enones, rather than 1,2 addition. Lithium dimethylcuprate exists as a dimer in diethyl ether forming an 8-membered ring. Lithium diphenylcuprate crystallizes as a dimeric etherate, 2.
If the Li+ ions is complexed with the crown ether 12-crown-4, the resulting diorganylcuprate anions adopt a linear coordination geometry at copper. More useful than the Gilman reagents are the so-called mixed cuprates with the formula − and 2−; such compounds are prepared by the addition of the organolithium reagent to copper halides and cyanide. These mixed cuprates are more stable and more purified. One problem addressed by mixed cuprates is the economical use of the alkyl group. Thus, in some applications, the mixed cuprate has the formula Li2 is prepared by combining thienyllithium and cuprous cyanide followed by the organic group to be transferred. In this higher order mixed cuprate, both the cyanide and thienyl groups do not transfer, only the R group does. Organolithium reagent Organocopper Grignard reagent Cuprate National Pollutant Inventory - Copper and compounds fact sheet
A cascade reaction known as a domino reaction or tandem reaction, is a chemical process that comprises at least two consecutive reactions such that each subsequent reaction occurs only in virtue of the chemical functionality formed in the previous step. In cascade reactions, isolation of intermediates is not required, as each reaction composing the sequence occurs spontaneously. In the strictest definition of the term, the reaction conditions do not change among the consecutive steps of a cascade and no new reagents are added after the initial step. By contrast, one-pot procedures allow at least two reactions to be carried out consecutively without any isolation of intermediates, but do not preclude the addition of new reagents or the change of conditions after the first reaction. Thus, any cascade reaction is a one-pot procedure, while the reverse does not hold true. Although composed of intramolecular transformations, cascade reactions can occur intermolecularly, in which case they fall under the category of multicomponent reactions.
The main benefits of cascade sequences include high atom economy and reduction of waste generated by the several chemical processes, as well as of the time and work required to carry them out. The efficiency and utility of a cascade reaction can be measured in terms of the number of bonds formed in the overall sequence, the degree of increase in the structural complexity via the process, its applicability to broader classes of substrates; the earliest example of a cascade reaction is arguably the synthesis of tropinone reported in 1917 by Robinson. Since the use of cascade reactions has proliferated in the area of total synthesis; the development of cascade-driven organic methodology has grown tremendously. This increased interest in cascade sequences is reflected by the numerous relevant review articles published in the past couple of decades. A growing area of focus is the development of asymmetric catalysis of cascade processes by employing chiral organocatalysts or chiral transition-metal complexes.
Classification of cascade reactions is sometimes difficult due to the diverse nature of the many steps in the transformation. K. C. Nicolaou labels the cascades as nucleophilic/electrophilic, pericyclic or transition-metal-catalyzed, based on the mechanism of the steps involved. In the cases in which two or more classes of reaction are included in a cascade, the distinction becomes rather arbitrary and the process is labeled according to what can be arguably considered the “major theme”. In order to highlight the remarkable synthetic utility of cascade reactions, the majority of the examples below come from the total syntheses of complex molecules. Nucleophilic/electrophilic cascades are defined as the cascade sequences in which the key step constitutes a nucleophilic or electrophilic attack. An example of such a cascade is seen in the short enantioselective synthesis of the broad-spectrum antibiotic -chloramphenicol, reported by Rao et al.. Herein, the chiral epoxy-alcohol 1 was first treated with dichloroacetonitrile in the presence of NaH.
The resulting intermediate 2 underwent a BF3·Et2O-mediated cascade reaction. Intramolecular opening of the epoxide ring yielded intermediate 3, after an in situ hydrolysis facilitated by excess BF3·Et2O, afforded -chloramphenicol in 71% overall yield. A nucleophilic cascade was employed in the total synthesis of the natural product pentalenene. In this procedure, squarate ester 5 was treated with propynyllithium; the two nucleophilic attacks occurred predominantly with trans addition to afford intermediate 6, which spontaneously underwent a 4π-conrotatory electrocyclic opening of the cyclobutene ring. The resulting conjugated species 7 equilibrated to conformer 8, which more underwent an 8π-conrotatory electrocyclization to the strained intermediate 9; the potential to release strain directed protonation of 9 such that species 10 was obtained selectively. The cascade was completed by an intramolecular aldol condensation that afforded product 11 in 76% overall yield. Further elaboration afforded the target -pentalenene.
A subcategory of nucleophilic/electrophilic sequences is constituted by organocatalytic cascades, in which the key nucleophilic attack is driven by organocatalysis. An organocatalytic cascade was employed in the total synthesis of the natural product harziphilone, reported by Sorensen et al. in 2004. Herein, treatment of the enone starting material 13 with organocatalyst 14 yielded intermediate 15 via conjugate addition. Subsequent cyclization by the intramolecular Michael addition of the enolate into the triple bond of the system gave species 16, which afforded intermediate 17 after proton transfer and tautomerization; the cascade was completed by elimination of the organocatalyst and a spontaneous 6π-electrocyclic ring closure of the resultant cis-dienone 18 to -harziphilone in 70% overall yield. An outstanding triple organocatalytic cascade was reported by Raabe et al. in 2006. Linear aldehydes, nitroalkenes and α,β-unsaturated aldehydes could be condensed together organocatalytically to afford tetra-substituted cyclohexane carbaldehydes with moderate to excellent diastereoselectivity and complete enantiocontrol.
The transformation is mediated by the available proline-derived organocatalyst 23. The transformation was proposed to proceed via a Michael addition/Michael addition/aldol condensation sequence. In the first step, Michael addition of aldehyde 20 to nitroalkene 21 occurs through enamine catalysis, yielding nitroalkane 25. Condensation of α,β-unsaturated aldehyde 22 with the organocatalyst facilitates the conjugate addition of 25 to giv
Syn and anti addition
In organic chemistry and anti addition are different ways in which two substituents can be added to a double bond or triple bond. This article will use cycloalkenes as examples. Syn addition is the addition of two substituents to the same side of a double bond or triple bond, resulting in a decrease in bond order but an increase in number of substituents; the substrate will be an alkene or alkyne. An example of syn addition would be the oxidation of an alkene to a diol via a suitable oxidizing agent such as Osmium tetroxide OsO4 or Potassium permanganate KMnO4. Anti addition is in direct contrast to syn addition. In anti addition, two substituents are added to opposite sides of a double bond or triple bond, once again resulting in a decrease in bond order and increase in number of substituents; the classical example of this is bromination of alkenes. Depending on the substrate double bond, addition can have different effects on the molecule. After addition to a straight-chain alkene such as C2H4, the resulting alkane will and rotate around its single sigma bond under normal conditions.
Thus whether substituents are added to the same side or opposite sides of a double can be ignored due to free rotation. However, if chirality or the specific absolute orientation of the substituents needs to be taken into account, knowing the type of addition is significant. Unlike straight-chain alkenes, cycloalkene syn addition allows stable addition of substituents to the same side of the ring, where they remain together; the cyclic locked ring structure prevents free rotation. Syn elimination and anti elimination are the reverse processes of anti addition; these result in a new double bond, such as in Ei elimination. IUPAC, Compendium of Chemical Terminology, 2nd ed.. Online corrected version: "endo, syn, anti". Doi:10.1351/goldbook. E02094
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 alkaline, alkaline earth, transition metals, sometimes broadened to include metalloids like boron and tin, as well. Aside from bonds to organyl fragments or molecules, bonds to'inorganic' carbon, like carbon monoxide, cyanide, or carbide, are considered to be organometallic as well; some related compounds such as transition metal hydrides and metal phosphine complexes are included in discussions of organometallic compounds, though speaking, they are not 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 and metal phosphine complexes are representative members of this class; the field of organometallic chemistry combines aspects of traditional inorganic and organic chemistry.
Organometallic compounds are used both stoichiometrically in research and industrial chemical reactions, as well as in the role of catalysts to increase the rates of such reactions, where target molecules include polymers and many other types of practical products. Organometallic compounds are distinguished by the prefix "organo-" e.g. organopalladium compounds. Examples of such organometallic compounds include all Gilman reagents, which contain lithium and copper. Tetracarbonyl nickel, ferrocene are examples of organometallic compounds containing transition metals. Other examples include organomagnesium compounds like iodomagnesium MeMgI, dimethylmagnesium, all Grignard reagents. In addition to the traditional metals, lanthanides and semimetals, elements such as boron, silicon and selenium are considered to form organometallic compounds, e.g. organoborane compounds such as triethylborane. Representative Organometallic Compounds Many complexes feature coordination bonds between a metal and organic ligands.
The organic ligands bind the metal through a heteroatom such as oxygen or nitrogen, in which case such compounds are considered coordination compounds. However, if any of the ligands form a direct M-C bond complex is considered to be organometallic, e.g. 2+. Furthermore, many lipophilic compounds such as metal acetylacetonates and metal alkoxides are called "metalorganics." A occurring transition metal alkyl complex is methylcobalamin, with a cobalt-methyl bond. This subset of complexes is discussed within the subfield of bioorganometallic chemistry. Illustrative of the many functions of the B12-dependent enzymes, the MTR enzyme catalyzes the transfer of a methyl group from a nitrogen on N5-methyl-tetrahydrofolate to the sulfur of homocysteine to produce methionine; the status of compounds in which the canonical anion has a delocalized structure in which the negative charge is shared with an atom more electronegative than carbon, as in enolates, may vary with the nature of the anionic moiety, the metal ion, the medium.
For instance, lithium enolates contain only Li-O bonds and are not organometallic, while zinc enolates contain both Zn-O and Zn-C bonds, are organometallic in nature. The metal-carbon bond in organometallic compounds is highly covalent. For electropositive elements, such as lithium and sodium, the carbon ligand exhibits carbanionic character, but free carbon-based anions are rare, an example being cyanide; as in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. The 18-electron rule is helpful in predicting the stabilities of metal carbonyls and related compounds. Most organometallic compounds do not however follow the 18e rule. Chemical bonding and reactivity in organometallic compounds is discussed from the perspective of the isolobal principle; as well as X-ray diffraction, NMR and infrared spectroscopy are common techniques used to determine structure. The dynamic properties of organometallic compounds is probed with variable-temperature NMR and chemical kinetics.
Organometallic compounds undergo several important reactions: oxidative addition and reductive elimination transmetalation carbometalation hydrometalation electron transfer β-hydride elimination organometallic substitution reaction carbon-hydrogen bond activation cyclometalation migratory insertion nucleophilic abstraction Early developments in organometallic chemistry include Louis Claude Cadet's synthesis of methyl arsenic compounds related to cacodyl, William Christopher Zeise's platinum-ethylene complex, Edward Frankland's discovery of diethyl- and dimethylzinc, Ludwig Mond's discovery of Ni4, Victor Grignard's organomagnesium compounds. The abundant and diverse products from coal and petroleum led to Ziegler–Natta, Fischer–Tropsch, hydroformylation catalysis which employ CO, H2, alkenes as feedstocks and ligands. Recognition of organometalli