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how these reactions are important in catalytic cycles. Chapter 15 focuses on parallels between organometallic chemistry and main group chemistry. Organometallic chemistry, the chemistry of compounds that contain metal–carbon bonds, twentieth century. It encompasses a wide variety of compounds and their reactions, inclu... | {
"Header 1": "[Organometallic Chemistry](#page-8-0)",
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The first organometallic compound to be reported was synthesized in 1827 by Zeise, who obtained yellow needle-like crystals after refluxing a mixture of PtCl<sub>4</sub> and PtCl<sub>2</sub> in ethanol, followed by addition of KCl solution. Zeise correctly asserted that this yellow product, subsequently dubbed *Zeise's... | {
"Header 1": "13.1 Historical Background",
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Some common organic ligands are shown in **Figure 13.7** . Special nomenclature has been devised to designate the manner in which some of these ligands bond to metal atoms; several of the ligands in Figure 13.7 may bond through different numbers of atoms. The number of atoms through which a ligand bonds is indicated by... | {
"Header 1": "13.2 **[Organic Ligands and Nomenclature](#page-8-0)**",
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A Cr atom has 6 electrons outside its noble gas core. Each CO is considered to act as a donor of 2 electrons. The total electron count is therefore:
Cr 6 electrons 6 (CO)
$$6 \times 2$$
electrons = $\frac{12 \text{ electrons}}{18 \text{ electrons}}$
Cr(CO)<sub>6</sub> is therefore considered an 18-electron complex... | {
"Header 1": "13.3.1 Counting Electrons",
"Header 3": "$Cr(CO)_6$",
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This method considers ligands to donate electron pairs to the metal. To determine the total electron count, we must take into account the charge on each ligand and determine the formal oxidation state of the metal.
Pentahapto- $C_5H_5$ is considered by this method as $C_5H_5^-$ , a donor of 3 electron pairs; it is ... | {
"Header 1": "13.3.1 Counting Electrons",
"Header 3": "Method A: Donor Pair Method",
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This method uses the number of electrons that would be donated by ligands *if they were neutral* . For simple inorganic ligands, this usually means that ligands are considered to donate the number of electrons equal to their negative charge as free ions. For example,
```
Cl is a 1@electron donor (charge on free ion =... | {
"Header 1": "13.3.1 Counting Electrons",
"Header 3": "*Method B: Neutral-Ligand Method*",
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Both methods of electron counting are illustrated for the following complexes.
| | Method A | | Method B | |
|------------------|--------------------|-------|---------------|-------|
| ClMn(CO)5 | Mn(I) | 6 e- | Mn | 7 e |
| ... | {
"Header 1": "13.3.1 Counting Electrons",
"Header 3": "**E X A M P L E 13 . 2**",
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An oversimplified rationale for the special significance of 18 electrons can be made by analogy with the octet rule in main group chemistry. If the octet represents a complete valence electron shell configuration ( $s^2p^6$ ), then the number 18 represents a filled valence shell for a transition metal $(s^2p^6d^{10})$... | {
"Header 1": "13.3.2 Why 18 Electrons?",
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Examples of square-planar complexes include the $d^8$ 16-electron complexes shown in Figure 13.10. To understand why 16-electron square-planar complexes might be especially stable, it is necessary to examine the molecular orbitals of such a complex. An energy diagram for the molecular orbitals of a square-planar mole... | {
"Header 1": "13.3.3 Square-Planar Complexes",
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It is useful to review the bonding in CO. The molecular orbital picture of CO shown in Figure 5.13 is similar to that of N2. Sketches of the molecular orbitals derived primarily from the 2 *p* atomic orbitals of these molecules are shown in **Figure 13.12** .
Two features of the molecular orbitals of CO deserve atten... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**Bonding**",
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N2 has molecular orbitals rather similar to those of CO, as shown in Figure 13.12 . Would you expect N2 to be a stronger or weaker p acceptor than CO?
**FIGURE 13.13** Sigma and Pi Interactions between CO and a Metal Atom.
If this picture of bonding between CO and metal atoms is corr... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**E X E R C I S E 13 . 4**",
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Predict which of the complexes $[V(CO)_6]^-$ , $Cr(CO)_6$ , or $[Mn(CO)_6]^+$ has the shortest C - O bond.
How is it possible for cationic carbonyl complexes such as $[Fe(CO)_6]^{2+}$ to have C - Ostretching bands even higher in energy than those in free CO? It seems clear that the CO ligand does not engage in ... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**EXERCISE 13.5**",
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Many cases are known in which CO forms bridges between two or more metals. Many bridging modes are known (Table 13.2).
TABLE 13.2 Bridging Modes of CO
| Type of CO | Approximate Range for v(CO) in Neutral<br>Complexes (cm <sup>-1</sup> ) |
|--------------------------------------... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**Bridging Modes of CO**",
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Binary carbonyls, containing only metal atoms and CO, are numerous. Representative binary carbonyl complexes are in Figure 13.16. Most of these complexes obey the 18-electron rule. The cluster compounds Co<sub>6</sub>(CO)<sub>16</sub> and Rh<sub>6</sub>(CO)<sub>16</sub> do not obey the rule, however. More detailed anal... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**Binary Carbonyl Complexes**",
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Verify the 18-electron rule for five of the binary carbonyls—other than $V(CO)_6$ , $Co_6(CO)_{16}$ , and $Rh_6(CO)_{16}$ —shown in Figure 13.16.
An interesting feature of the structures of binary carbonyl complexes is that the tendency of CO to bridge transition metals decreases going down the periodic table. For... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**EXERCISE 13.6**",
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One additional aspect of CO as a ligand deserves mention: it can sometimes bond through oxygen as well as carbon. This phenomenon was first noted in the ability of the oxygen of a metal–carbonyl complex to act as a donor toward Lewis acids such as AlCl3, with the overall function of CO serving as a bridge between the t... | {
"Header 1": "13.4.1 **[Carbonyl \\(CO\\) Complexes](#page-9-0)**",
"Header 3": "**Oxygen-Bonded Carbonyls**",
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Several diatomic ligands similar to CO are worth mention. Three—CS (thiocarbonyl), CSe (selenocarbonyl), and CTe (tellurocarbonyl)—are of interest in part for purposes of comparison with CO. The realm of CS complexes has been explored extensively since the first thiocarbonyl complex was reported in 1966, 14 but the che... | {
"Header 1": "13.4.2 Ligands Similar to CO",
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The NO (nitrosyl) ligand shares many similarities with CO. Like CO, it is a $\sigma$ donor and $\pi$ acceptor and can serve as a terminal or bridging ligand; useful information can be obtained about its compounds by analysis of its infrared spectra. Unlike CO, however, terminal NO has two common coordination modes,... | {
"Header 1": "13.4.2 Ligands Similar to CO",
"Header 3": "**NO Complexes**",
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Although hydrogen atoms form bonds with nearly every element, we will specifically consider coordination compounds containing H bonded to transition metals.<sup>21</sup> Because the hydrogen atom only has a 1s orbital of suitable energy for bonding, the bond between H and a transition metal must be a $\sigma$ interac... | {
"Header 1": "13.4.3 Hydride and Dihydrogen Complexes",
"Header 3": "**Hydride Complexes**",
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Although complexes containing H<sub>2</sub> molecules coordinated to transition metals had been proposed for many years, the first structural characterization of a dihydrogen complex did not occur until 1984, when Kubas synthesized $M(CO)_3(PR_3)_2(H_2)$ , where M = Mo or W and R = cyclohexyl or isopropyl.<sup>23</sup... | {
"Header 1": "13.4.3 Hydride and Dihydrogen Complexes",
"Header 3": "**Dihydrogen Complexes**",
"token_count": 428,
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Although it is relatively simple to describe pictorially how ligands such as CO and PPh<sub>3</sub> bond to metals, explaining bonding between metals and organic ligands having extended $\pi$ systems can be more complex. For example, how are the $C_5H_5$ rings attached to Fe in ferrocene, and how can 1,3-butadiene ... | {
"Header 1": "13.4.4 Ligands Having Extended Pi Systems",
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The simplest case of an organic molecule having a linear p system is ethylene, which has a single p bond resulting from the interactions of two 2 *p* orbitals on its carbon atoms. Interactions of these *p* orbitals result in one bonding and one antibonding p orbital, as shown:
The anti... | {
"Header 1": "13.4.4 Ligands Having Extended Pi Systems",
"Header 3": "**Linear Pi Systems \\***",
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The procedure for obtaining a pictorial representation of the orbitals of cyclic $\pi$ systems of hydrocarbons is similar to the procedure for the linear systems. The smallest such cyclic hydrocarbon is cyclo- $C_3H_3$ . The lowest energy $\pi$ molecular orbital for this system is the one resulting from constructiv... | {
"Header 1": "13.4.4 Ligands Having Extended Pi Systems",
"Header 3": "**Cyclic Pi Systems**",
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Many complexes involve ethylene, $C_2H_4$ , as a ligand, including the anion of Zeise's salt, $[Pt(\eta^2-C_2H_4)Cl_3]^-$ . In such complexes, ethylene commonly acts as a sidebound ligand with the following geometry with respect to the metal:
**FIGURE... | {
"Header 1": "13.5.1 Linear Pi Systems",
"Header 3": "**Pi-Ethylene Complexes**",
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The allyl group most commonly functions as a trihapto ligand, using delocalized p orbitals as described previously, or as a monohapto ligand, primarily s bonded to a metal. Examples of these types of coordination are in **Figure 13.24** .
Bonding between h<sup>3</sup> @C3H5 and a metal atom is shown schematically in ... | {
"Header 1": "13.5.1 Linear Pi Systems",
"Header 3": "**Pi–Allyl Complexes**",
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The cyclopentadienyl group, C<sub>5</sub>H<sub>5</sub>, may bond to metals in a variety of ways, with many examples known of the $\eta^1$ -, $\eta^3$ -, and $\eta^5$ -bonding modes. The discovery of the first cyclopentadienyl complex, ferrocene, was a landmark in the development of organometallic chemistry and stimu... | {
"Header 1": "13.5.2 Cyclic Pi Systems",
"Header 3": "**Cyclopentadienyl (Cp) Complexes**",
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Ferrocene is the prototype of a series of sandwich compounds, the metallocenes, with the formula $(C_5H_5)_2M$ . Electron counting in ferrocene can be viewed in two ways. One possibility is to consider it an iron(II) complex with two 6-electron cyclopentadienide ( $C_5H_5^-$ ) ions, another to view it as iron(0) coord... | {
"Header 1": "13.5.2 Cyclic Pi Systems",
"Header 3": "Ferrocene, $(\\eta^5 - C_5 H_5)_2 Fe$",
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Determine which orbitals on Fe are appropriate for interaction with each of the remaining group orbitals in Figure 13.27 .
The complete energy-level diagram for the molecular orbitals of ferrocene is shown in **Figure 13.28** . The molecular orbital resulting from the *dyz* bonding interaction, labeled **1** in the M... | {
"Header 1": "13.5.2 Cyclic Pi Systems",
"Header 3": "**E X E R C I S E 13 . 9**",
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Other metallocenes have similar structures but do not necessarily obey the rule. For example, cobaltocene and nickelocene are structurally similar 19- and 20-electron species.
FIGURE 13.29 Molecular Orbitals of Ferrocene Having Greatest d Character.
<sup>\*</sup>The relative energies... | {
"Header 1": "13.5.2 Cyclic Pi Systems",
"Header 3": "**Other Metallocenes and Related Complexes**",
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Many complexes are known containing both Cp and CO ligands. These include "half-sandwich" compounds such as $(\eta^5\text{-}C_5H_5)\text{Mn}(\text{CO})_3$ and dimeric and larger cluster molecules. Examples are in **Figure 13.35**. As for the binary CO complexes, complexes of the second- and third-row transition metal... | {
"Header 1": "13.5.2 Cyclic Pi Systems",
"Header 3": "**Complexes Containing Cyclopentadienyl and CO Ligands**",
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As immense pi systems, fullerenes were recognized early as ligands to transition metals. Fullerene-metal compounds\* have been prepared for a variety of metals. These compounds fall into several structural types:
• Adducts to the oxygens of osmium tetroxide. 33
**Example:** $C_{60}(OsO_4)(4-t-butylpyridine)_2$
•... | {
"Header 1": "13.5.3 Fullerene Complexes",
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As a ligand, C<sub>60</sub> behaves primarily as an electron-deficient alkene (or arene), and it bonds to metals in a dihapto fashion through a C—C bond at the fusion of two 6-membered rings (**Figure 13.38**). There are also instances in which $C_{60}$ bonds in a pentahapto or hexahapto fashion.
Dihapto bonding wa... | {
"Header 1": "13.5.3 Fullerene Complexes",
"Header 3": "Fullerenes as Ligands<sup>39</sup>",
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These complexes are "cage" organometallic complexes in which the metal is completely surrounded by the fullerene. Typically, complexes containing encapsulated metals are prepared by laser-induced vapor phase reactions between carbon and the metals. These compounds contain central metal cations surrounded by a fulleride... | {
"Header 1": "13.5.3 Fullerene Complexes",
"Header 3": "Complexes with Encapsulated Metals\\*",
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Some of the earliest known organometallic complexes were those having $\sigma$ bonds between main group metal atoms and alkyl groups. Examples include Grignard reagents, having magnesium-alkyl bonds, and alkyl complexes with alkali metals, such as methyllithium.
Stable transition-metal alkyls were initially synthes... | {
"Header 1": "13.6 Complexes Containing M - C, M = C, and M≡C Bonds",
"Header 3": "13.6.1 Alkyl and Related Complexes",
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Carbene complexes contain metal–carbon double bonds. \* First synthesized in 1964 by Fischer, 46 carbene complexes are known for the majority of transition metals and for a wide range of carbene ligands, including the simple carbene, :CH2. The majority of such complexes contain one or two highly electronegative heteroa... | {
"Header 1": "13.6.2 **[Carbene Complexes](#page-9-0)**",
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$$(OC)_5Cr = C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longleftrightarrow (OC)_5Cr - C \longl... | {
"Header 1": "13.6.2 **[Carbene Complexes](#page-9-0)**",
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Carbyne complexes have metal–carbon triple bonds; they are formally analogous to alkynes. \* Many carbyne complexes are now known; examples of carbyne ligands include the following:
$$M \equiv C - R$$
where R = aryl, alkyl, H, SiMe3, NEt2, PMe2, SPh, or Cl. Carbyne complexes were first synthesized fortuitously as p... | {
"Header 1": "13.6.3 **[Carbyne \\(Alkylidyne\\) Complexes](#page-9-0)**",
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The simplest possible carbon-containing ligand, a single carbon atom, is known, and the number of complexes of such **carbide**, **carbido**, or simply **carbon** ligands has grown considerably in the past decade. Although it is tempting, by extending the series $-CR_3$ , $=CR_2$ , =CR, to assign a quadruple bond to ... | {
"Header 1": "13.6.4 Carbide and Cumulene Complexes",
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transition-metal complexes with $M \equiv N$ and M = O bonds.<sup>55</sup> In addition, the frontier orbitals of the carbide complex in Figure 13.48 (where R = methyl) have many similarities to those of CO, suggesting that such complexes may potentially show similar coordination chemistry to the carbonyl ligand.<sup>... | {
"Header 1": "13.6.4 Carbide and Cumulene Complexes",
"Header 3": "FIGURE 13.49 A Metallacumulene Complex.",
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Unsaturated carbon and hydrocarbon bridges have been studied in recent years in connection with their potential to serve as wires joining metal centers in molecular electronics. The most widely studied types of these bridges have been the **polyynediyl** bridges with alternating single and triple bonds and **polyenediy... | {
"Header 1": "13.6.5 Carbon Wires: Polyyne and Polyene Bridges",
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The Covalent Bond Classification (CBC) Method\* is an insightful approach specifically designed for covalent molecules and is particularly applicable to organometallic compounds. The conceptual core of the CBC method is to classify each ligand as a *neutral* species on the basis of its orbital interactions with the met... | {
"Header 1": "13.7 Covalent Bond Classification Method",
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Determine the equivalent neutral class CBC formulas of Cr(h<sup>6</sup> @C6H6)2 , [Mo(CO)3(h<sup>5</sup> @C5H5)]- , WH2(h<sup>5</sup> @C5H5)2 , and [FeCl4] <sup>2</sup>- .
The equivalent neutral class formula ( [ML*<sup>l</sup>* X*x*Z*z*] ) permits comparison of these iron complexes, and provides ready access to othe... | {
"Header 1": "13.7 Covalent Bond Classification Method",
"Header 3": "**E X E R C I S E 13 .11**",
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One of the most challenging aspects of organometallic research is the characterization of new products. Assuming that pure products can be isolated by chromatography, recrystallization, or other techniques, determining the structure can present a challenge. Many complexes can be crystallized and characterized by X-ray ... | {
"Header 1": "13.8 **[Spectral Analysis and Characterization of](#page-9-0) Organometallic Complexes**",
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Two geometries, linear and bent, must be considered:
$$O-C-M-C-O$$
$C$
$C$
$C$
In the case of two CO ligands arranged linearly, only an antisymmetric vibration of the ligands is IR active; a symmetric vibrational mode produces no change in dipole moment and hence is inactive. However, if two CO ligands are oriented... | {
"Header 1": "13.8.1 **[Infrared Spectra](#page-9-0)**",
"Header 3": "**Dicarbonyl Complexes**",
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Here, the predictions are not quite so simple. The exact number of carbonyl bands can be determined according to the symmetry approach of Chapter 4. For convenient reference, the numbers of bands expected for a variety of CO complexes are in Table 13.10. In carbonyl complexes, the number of C—O stretching bands cannot ... | {
"Header 1": "13.8.1 **[Infrared Spectra](#page-9-0)**",
"Header 3": "Complexes containing three or more carbonyls",
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The complex Mo(CO)<sub>3</sub>(NCC<sub>2</sub>H<sub>5</sub>)<sub>3</sub> has the infrared spectrum in the margin. Is this complex more likely the *fac* or *mer* isomer?
**TABLE 13.10 Carbonyl Stretching Bands**
| TABLE 13.10 Carbonyl Stre | etenning banius | Coordination Number ... | {
"Header 1": "13.8.1 **[Infrared Spectra](#page-9-0)**",
"Header 3": "**EXERCISE 13.12**",
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We have already encountered two examples in which the position of the carbonyl stretching band provides useful information. In the case of the isoelectronic species $[Mn(CO)_6]^+$ , $Cr(CO)_6$ , and $[V(CO)_6]^-$ , an increase in negative charge on the complex causes a significant reduction in the energy of the C-O ... | {
"Header 1": "13.8.1 **[Infrared Spectra](#page-9-0)**",
"Header 3": "**Positions of IR Bands**",
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Although the isotope 13C has a low natural abundance (approximately 1.1%) and low sensitivity for the NMR experiment (about 1.6% as sensitive as <sup>1</sup> H ), Fourier transform techniques make it possible to obtain useful 13C spectra for most organometallic species of reasonable stability. Nevertheless, the time ne... | {
"Header 1": "13.8.2 **[NMR Spectra](#page-9-0)**",
"Header 3": "**13C NMR**",
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$(C_5H_5)_2Fe(CO)_2$ has interesting NMR behavior. This compound contains both $\eta^1$ - and $n^5$ -C<sub>5</sub>H<sub>5</sub> ligands. The <sup>1</sup>H NMR spectrum at room temperature shows two singlets of equal area. A singlet would be expected for the five equivalent protons of the $n^5$ -C<sub>5</sub>H<sub>5... | {
"Header 1": "13.8.2 **[NMR Spectra](#page-9-0)**",
"Header 3": "**Molecular Rearrangement Processes**",
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$[(C_5H_5)Mo(CO)_3]_2$ reacts with tetramethylthiuramdisulfide (tds) in refluxing toluene to give a molybdenum-containing product having the following characteristics:
<sup>1</sup>H NMR: Two singlets, at $\delta$ 5.48 (relative area = 5) and $\delta$ 3.18 (relative area = 6). (For comparison, [(C<sub>5</sub>H<su... | {
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"Header 3": "**EXAMPLE 13.3**",
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When a toluene solution containing I and excess triphenylphosphine is heated to reflux, first compound II is formed, and then compound III. II has infrared bands at 2038, 1958, and 1906 cm<sup>-1</sup>; **III** at 1944 and 1860 cm<sup>-1</sup>. ${}^{1}$ H and ${}^{13}$ C NMR data [ $\delta$ values (relative area)] a... | {
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"Header 3": "**EXAMPLE 13.4**",
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This is a good example of the utility of <sup>13</sup>C NMR. Both **II** and **III** have peaks with similar chemical shifts to the peak at $\delta$ 224.31 for **I**, suggesting that the carbene ligand is retained in the reaction. Similarly, II and III have peaks near $\delta$ 73.33, a further indication that the c... | {
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"Header 3": "Identify II and III.",
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- 1. W. C. Zeise, *Ann. Phys. Chem.*, **1831**, *21*, 497–541. A translation of excerpts from this paper can be found in G. B. Kauffman, ed., *Classics in Coordination Chemistry*, Part 2, Dover, New York, 1976, pp. 21–37. A review of the history of the anion of Zeise's salt, including some earlier references, has been ... | {
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Ed.* , **2009** , *48* , 4109.
- **32.** S. Krieck, H. Görls, L. Yu, M. Reiher, M. Westerhausen, *J. Am. Chem. Soc.* , **2009** , *131* , 2977; S. Krieck, H. Görls, M. Westerhausen, *J. Am. Chem. Soc.* , **2010** , *132* , 12492.
- **33.** J. M. Hawkins, A. Meyer, T. A. Lewis, S. D. Loren, F. J. Hollander, *Science* , ... | {
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Ishii, *Organometallics* , **2010** , *29* , 519.
- **58.** M. I. Bruce, *Coord. Chem. Rev.* , **2004** , *248* , 1603.
- **59.** V. Cadierno J. Gimeno, *Chem. Rev* ., **2009** , *109* , 3512.
- **60.** M. Dede, M. Drexler, H. Fischer, *Organometallics* , **2007** , *26* , 4294.
- **61.** C. Coletti, A. Marrone, N. Re,... | {
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"Header 3": "References",
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Much information on organometallic compounds is included in two general inorganic references, N. N. Greenwood and A. Earnshaw, *Chemistry of the Elements*, 2nd ed., Butterworth Heinemann, Oxford, 1997, and F. A. Cotton, G. Wilkinson, C. A. Murillo, and M. Bochman, *Advanced Inorganic Chemistry*, 6th ed., Wiley InterSci... | {
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- **13.1** Which of the following obey the 18-electron rule?
- a. Fe(CO)<sub>5</sub>
- **b.** $[Rh(bipy)_2Cl]^+$
- c. $(\eta^5 Cp^*)Re(=O)_3$ , where $Cp^* = C_5(CH_3)_5$
- d. Re(PPh<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>N
- e. $Os(CO)(\equiv CPh)(PPh_3)_2Cl$
- **f.** The CE complexes in Table 13.3
- **13.2** Which... | {
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Account for the following trend in IR frequencies:
$$[Cr(CN)_5(NO)]^{4-}$$
$\nu$ (NO) = 1515 cm<sup>-1</sup>
$[Mn(CN)_5(NO)]^{3-}$ $\nu$ (NO) = 1725 cm<sup>-1</sup>
$[Fe(CN)_5(NO)]^{2-}$ $\nu$ (NO) = 1939 cm<sup>-1</sup>
- **b.** The ion [RuCl(NO)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>]<sup>+</sup> has N O... | {
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Chem.*, 1996, *35*, 7468.)
- **13.28** Account for the observation that $[Co(CO)_3(PPh_3)_2]^+$ has only a single carbonyl stretching frequency.
- 13.29 In addition to the hexacarbonyl complexes shown in Section 13.4.1, the ion [Ir(CO)<sub>6</sub>]<sup>3+</sup> has been reported. Predict the position of the carbonyl ... | {
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When Cr(CO)<sub>5</sub>(PH<sub>3</sub>) is oxidized, what is the effect on the Cr—P distance? Explain briefly.
- **d.** When Cr(CO)<sub>5</sub>(NH<sub>3</sub>) is oxidized, what is the effect on the Cr—N distance? Explain briefly. (T. Leyssens, D. Peeters, A. G. Orpen, J. N. Harvey, *New J. Chem.*, **2005**, *29*, 1424... | {
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Templeton, *Organometallics*, 1983, 2, 168.)
- **13.49** Photolysis at -78 °C of $[(\eta^5-C_5H_5)Fe(CO)_2]_2$ results in the loss of a colorless gas and the formation of an iron-containing product having a single carbonyl band at $1785 \text{ cm}^{-1}$ and containing 14.7 percent oxygen by mass. Suggest a structur... | {
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If 0.00100 mmol of $[CpMo(CO)_3]_2$ and 0.00200 mmol of $[CpW(CO)_3]_2$ are dissolved in toluene until equilibrium is achieved, calculate the amounts of the three organometallic complexes in the equilibrium solution. (See T. Madach, H. Vahrenkamp, *Z. Naturforsch.*, **1979**, *34b*, 573.)
- 13.57 Addition of BH<s... | {
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- **13.62 a.** Generate and display the $\pi$ and $\pi^*$ orbitals of the cyclopentadienyl group, $C_5H_5$ . Compare the results with the diagrams in Figure 13.22. Identify the nodes that cut through the plane of the atoms.
- **b.** Generate and display the molecular orbitals of ferrocene. Identify the molecular o... | {
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Many reactions of organometallic compounds involve a change in metal coordination number by a gain or loss of ligands. If the oxidation state of the metal is retained, these reactions are considered addition or dissociation reactions; if the metal oxidation state is changed, they are termed oxidative additions or reduc... | {
"Header 1": "14.1 Reactions Involving Gain or Loss of Ligands",
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#### **CO Dissociation**
Chapter 13 introduced carbonyl dissociation reactions, in which CO may be lost thermally or photochemically. Such a reaction may result in rearrangement of the remaining molecule or replacement of CO by another ligand:
$$\begin{array}{c|c}
& & & & & & & & & & & & & & & & & & &$$
$$Fe(CO)_... | {
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Ligands other than carbon monoxide can dissociate, with the ease of dissociation a function of the strength of metal-ligand bonding. The metal-ligand bond strength depends on an interplay of electronic effects (for example, the match of energies of the metal and ligand
<sup>\*</sup>Assuming that no oxidation-reductio... | {
"Header 1": "14.1.1 Ligand Dissociation and Substitution",
"Header 3": "**Dissociation of Phosphine**",
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A classic example of ligand steric bulk influencing ligand substitution reaction rates is
$$cis$$
-Mo(CO)<sub>4</sub>L<sub>2</sub> + CO $\longrightarrow$ Mo(CO)<sub>5</sub>L + L (L = phosphine or phosphite)
The rate of this reaction, which is first order in cis-Mo(CO)<sub>4</sub>L<sub>2</sub>, increases with in... | {
"Header 1": "14.1.1 Ligand Dissociation and Substitution",
"Header 3": "**Dissociation of Phosphine**",
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These reactions involve an increase in both the oxidation state and the coordination number of the metal. Oxidative addition (OA) reactions are essential steps in many catalytic processes. The reverse reaction, designated reductive elimination (RE), is also very important. These reactions are described schematically by... | {
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"Header 3": "14.1.2 Oxidative Addition and C—H Bond Activation",
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These are reactions that incorporate metals into organic rings. Orthometallations, oxidative additions in which an ortho position of an aromatic ring becomes attached to the metal, are quite common. The first Figure 14.5 example features oxidative addition in which the ortho carbon to the phosphorus of a triphenylphosp... | {
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"Header 3": "Cyclometallations",
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Reductive elimination is the reverse of oxidative addition. To illustrate this distinction, consider the following equilibrium:
$$(\eta^5-C_5H_5)_2TaH + H_2 \xrightarrow{OA} (\eta^5-C_5H_5)_2TaH_3$$
$$Ta(III) Ta(V)$$
The forward reaction involves formal oxidation of the metal, accompanied by an increase in coordi... | {
"Header 1": "14.1.3 Reductive Elimination and Pd-Catalyzed Cross-Coupling",
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All the C—H bond activation examples given in Sections 14.1.2 and 14.1.3 exhibit the classic characteristics of oxidative addition and involve metal centers with eight valence electrons (Ir(I), Pd(II), Fe(0)). These metals have relatively low oxidation states and are predisposed toward being able to oxidize C—H bonds.\... | {
"Header 1": "14.1.3 Reductive Elimination and Pd-Catalyzed Cross-Coupling",
"Header 3": "14.1.4 Sigma Bond Metathesis",
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addition/reductive elimination or sigma-bond metathesis.
A significant current focus in organometallic chemistry is the design of pincer ligands that provide constrained metal geometries and afford complexes with frontier orbitals of proper energy and symmetry to permit useful stoichiometric and catalytic reactivity.... | {
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Carbonyl insertion, the reaction of CO with an alkyl complex to give an acyl [—C(=O)R] product, has been well-studied. The reaction of $CH_3Mn(CO)_5$ with CO is an excellent example:
$$H_3C-Mn(CO)_5 + CO \longrightarrow CH_3C-Mn(CO)_5$$
FIGURE 14.11 Examples of 1,2 Insertion Reactions.
$$\begin{array}{ccccccccc... | {
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#### **CO Insertion Reactions** Mechanism 1
$$\begin{array}{cccccccccccccccccccccccccccccccccccc$$
$$\begin{array}{c} \text{Mechanism 2} \\ \begin{array}{c} O \\ C \\ OC \\ OC \\ OC \\ OC \\ OC \\ OC \\$$
$$\begin{array}{c} \text{Mechanism 3} \\ \begin{array}{c} O \\ C \\ C \\ \end{array} \\ \begin{array}{c} O \\... | {
"Header 1": "14.2.2 Carbonyl Insertion (Alkyl Migration)",
"Header 3": "FIGURE 14.12 Possible Mechanisms for CO Insertion Reactions. Acyl groups are −CH<sub>3</sub> for clarity; the actual geometry around acyl carbons is trigonal.",
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Mechanism 1 is definitely ruled out by the first experiment. Direct insertion of <sup>13</sup>CO must result in <sup>13</sup>C in the acyl ligand, but none is found. Mechanisms 2 and 3 are both compatible with the results of this experiment.
The principle of microscopic reversibility requires that any reversible reac... | {
"Header 1": "14.2.2 Carbonyl Insertion (Alkyl Migration)",
"Header 3": "FIGURE 14.12 Possible Mechanisms for CO Insertion Reactions. Acyl groups are −CH<sub>3</sub> for clarity; the actual geometry around acyl carbons is trigonal.",
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Show that heating of $CH_3^{13} \stackrel{\parallel}{C} - Mn(CO)_5$ would not be expected to give the *cis* product by mechanism 1.
The third experiment differentiates conclusively between mechanisms 2 and 3. The CO migration of mechanism 2, with <sup>13</sup>CO cis to the acyl ligand, requires migration of
#### ... | {
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"Header 3": "**EXERCISE 14.1**",
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Hydride elimination reactions are characterized by hydrogen atom transfer from a ligand to a metal. The most common type of hydride elimination is $\beta$ elimination, with a proton in a $\beta$ position\* on an alkyl ligand transferred to the metal by way of an intermediate in which the metal, the $\alpha$ and ... | {
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Organometallic reactions are of great interest industrially. The commercial interest in catalysis has been spurred by the fundamental problem of how to convert relatively inexpensive feedstocks (e.g., coal, petroleum, and water) into molecules of greater commercial value. This frequently involves conversion of simple m... | {
"Header 1": "14.3 Organometallic Catalysts",
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If deuterium gas (D<sub>2</sub>) is bubbled through a benzene solution of $(\eta^5-C_5H_5)_2TaH_3$ at an elevated temperature, the hydrogen atoms of benzene are slowly replaced by deuterium; eventually, perdeuterobenzene, C<sub>6</sub>D<sub>6</sub>, an NMR solvent, can be obtained. <sup>19</sup> Replacement of hydrog... | {
"Header 1": "14.3.1 Catalytic Deuteration",
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The hydroformylation, or oxo, process was introduced in 1938 and is the oldest homogeneous catalytic process in commercial use. It is used to convert terminal alkenes into aldehydes and other organic products, especially those having their carbon chain increased by one. Approximately 10 million tons of hydroformylation... | {
"Header 1": "14.3.2 Hydroformylation",
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Hydroformylation (Oxo) Process
$$R_{2}C = CH_{2} + CO + H_{2} \quad \frac{HCo(CO)_{4}}{\Delta, \text{ high } P} \qquad R_{2}CH - CH_{2} - C - H$$
$$HCo(CO)_{4} \qquad \qquad | 18e^{-}$$
$$O \qquad \qquad | 16e^{-}$$
$$O \qquad \qquad | 16e^{-}$$
$$O \qquad \qquad | 16e^{-}$$
$$O \qquad \qquad | 16e^{-}$$ ... | {
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Parshall and S. D. Ittel, Homogeneous Catalysis, 2nd ed., John Wiley & Sons, New York, 1992, pp. 106-111.
Because linear products are generally more valuable, a challenge in the development of hydroformylation has been to design processes with high linear to branched ratios.
Detailed calculations of the geometries ... | {
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Show how $(CH_3)_2CHCH_2CHO$ can be prepared from $(CH_3)_2C=CH_2$ by the hydroformylation process.
A shortcoming of the cobalt carbonyl-based hydroformylation process is that it produces only about 80 percent of the much more valuable linear aldehydes, with the remainder having branched chains. Modifying the cat... | {
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"Header 3": "**EXERCISE 14.4**",
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Classify each step of the mechanism in Figure 14.19 according to its reaction type.
More recently, higher linear to branched ratios for rhodium-catalyzed hydroformylation have been achieved using bidentate ligands, which broaden the range of steric and electronic options available. For example, the BISBI ligand has e... | {
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The synthesis of acetic acid from methanol and CO is a process that has been used with commercial success by Monsanto. The mechanism of this process is complex; a proposed outline is in Figure 14.20. The individual steps are the characteristic types of organometallic reactions described previously; the intermediates ar... | {
"Header 1": "14.3.3 Monsanto Acetic Acid Process",
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The Wacker or Smidt process, used to synthesize acetaldehyde from ethylene, involves a catalytic cycle that uses PdCl<sub>4</sub><sup>2-</sup>. A fiftieth-anniversary retrospective by a coauthor of the original report<sup>36</sup> on this process was published in 2009.<sup>37</sup> Figure 14.21 outlines a proposed cycl... | {
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"Header 3": "14.3.4 Wacker (Smidt) Process",
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Wilkinson's catalyst, RhCl(PPh3)3, participates in the same types of reactions as expected for 4-coordinate organometallic compounds; for example, many reactions bear similarities to Vaska's catalyst, *trans*@IrCl(CO)(PPh3)2. RhCl(PPh3)3 participates in a variety of catalytic and noncatalytic processes. The bulky phosp... | {
"Header 1": "14.3.5 **[Hydrogenation by Wilkinson's Catalyst](#page-9-0)**",
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Olefin metathesis, first discovered in the 1950s, involves the formal exchange of :CR2 fragments ( R = H or alkyl) between alkenes, also known as olefins. For example, metathesis between molecules of formula H2C " CH2 and HRC " CHR would yield two H2C " CHR molecules:
$$\begin{array}{cccc} \mathbf{H_2} & \mathbf{HR} ... | {
"Header 1": "14.3.6 **[Olefin Metathesis](#page-9-0)**",
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Predict the possible products of metathesis of the following olefi ns. Be sure to consider that two molecules of the same structure can also metathesize (undergo self-metathesis).
**a.** Between propene and 1-butene. +
**b.** Between ethylene and cyclohexene. +
$$\| + \bigcirc \lon... | {
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This proposed mechanism was investigated by reacting two 2-butenes, H3CiCH"CHiCH3 and the fully deuterated D3CiCD"CDiCD3. If alkyl transfer could occur, iCH3 and iCD3 groups would be expected to exchange, giving mixtures of H and D atoms on each side of the double bond ("CHiCD3 and "CDiCH3). The result ( **Figure 14.25... | {
"Header 1": "14.3.6 **[Olefin Metathesis](#page-9-0)**",
"Header 3": "**Alkyl Exchange**",
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Bradshaw proposed that "the dismutation of olefins should proceed via a quasicyclobutane intermediate."43 In this mechanism, the two alkenes would first coordinate to a transition metal, forming a quasicyclobutane (Figure 14.26), after which the metal-complex intermediate would break apart to form the new alkenes. Beca... | {
"Header 1": "14.3.6 **[Olefin Metathesis](#page-9-0)**",
"Header 3": "**Diolefin (Pairwise) Mechanism**",
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Hérisson and Chauvin proposed that metathesis reactions are catalyzed by carbene (alkylidene) complexes that react with alkenes via the formation of a cyclic intermediate, a metallacyclobutane, as shown in Figure 14.24c. In this mechanism, a metal carbene complex first reacts with an alkene to form the metallacyclobuta... | {
"Header 1": "14.3.6 **[Olefin Metathesis](#page-9-0)**",
"Header 3": "Carbene (Non-Pairwise) Mechanism",
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$$(CO)_5W \longrightarrow H_2C \longrightarrow (CO)_5W \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrightarrow H_2C \longrighta... | {
"Header 1": "14.3.6 **[Olefin Metathesis](#page-9-0)**",
"Header 3": "Carbene (Non-Pairwise) Mechanism",
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A reaction utilizing this catalyst is a critical step of the synthesis of the natural product dactylol (Figure 14.31).<sup>47</sup>
The Figure 14.31 reaction is an example of ring-closing metathesis (RCM), in which the metathesis of two double bonds leads to ring formation. Like ordinary metathesis, ringclosing metat... | {
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"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
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In 1955, Ziegler and coworkers reported that solutions of TiCl4 in hydrocarbon solvents in the presence of Al(C2H5)3 gave heterogeneous mixtures capable of polymerizing ethylene.55 Subsequently, many other heterogeneous processes were developed for polymerizing alkenes, using aluminum alkyls in combination with transit... | {
"Header 1": "14.4.1 **[Ziegler–Natta Polymerizations](#page-9-0)**",
"token_count": 864,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
This reaction occurs at elevated temperatures and pressures between water (steam) and natural sources of carbon, such as coal or coke:
$$H_2O + C \longrightarrow H_2 + CO$$
The products of this reaction, an equimolar mixture of H<sub>2</sub> and CO, called synthesis gas or syn gas (some CO<sub>2</sub> may be produc... | {
"Header 1": "14.4.2 Water Gas Reaction",
"token_count": 838,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
- **1.** W. D. Covey, T. L. Brown, *Inorg. Chem.* , **1973** , *12* , 2820.
- **2.** C. A. Tolman, *J. Am. Chem. Soc.* , **1970** , *92* , 2956; *Chem. Rev.* , **1977** , *77* , 313. K. A. Bunten, L. Chen, A. L. Fernandez, A. J. Poë, *Coord. Chem. Rev.* , **2002** , *233* – *234* , 41.
- **3.** H. Clavier, S. P. Nolan,... | {
"Header 1": "14.4.2 Water Gas Reaction",
"Header 3": "**References**",
"token_count": 1959,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
Claver, *Tetrahedron: Asymmetry* , **2010** , *21* , 1135.
- **33.** M. Cheong, R. Schmid, T. Ziegler, *Organometallics* , **2000** , *19* , 1973 and references therein.
- **34.** J. Forster, *J. Chem. Soc., Dalton Trans.* , **1979** , 1639; A. Haynes, et al., *J. Am. Chem. Soc.* , **2004** , *126* , 2847.
- **35.** A.... | {
"Header 1": "14.4.2 Water Gas Reaction",
"Header 3": "**References**",
"token_count": 1975,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
Miessler, Organometallic Chemistry, Prentice Hall, Upper Saddle River, NJ, 1997, pp. 357–369.
- 61. W. H. Turner, R. R. Schrock, J. Am. Chem. Soc., 1982, 104, 2331.
- **62.** E. Fischer, H. Tropsch, *Brennst. Chem.*, **1923**, *4*, 276.
- 63. M. M. Taqui Khan, S. B. Halligudi, S. Shukla, Angew. Chem., Int. Ed., 1988, 2... | {
"Header 1": "14.4.2 Water Gas Reaction",
"Header 3": "**References**",
"token_count": 247,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
J. F. Hartwig, Organotransition Metal Chemistry, From Bonding to Catalysis, University Science Books, Mill Valley, CA, 2010, provides a detailed discussion, with numerous references, of many of the reactions and catalytic processes described in this chapter, as well as a variety of other types of organometallic reactio... | {
"Header 1": "14.4.2 Water Gas Reaction",
"Header 3": "**General References**",
"token_count": 381,
"source_pdf": "datasets/websources/biochem/inorganic-chemistry-g-l-miessler-2014.pdf"
} |
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