Trimethylenemethane complexes are metal complexes of the organic compound]] trimethylenemethane. Several examples are known, and some have been employed in organic synthesis. [1]
The synthesis of cyclobutadieneiron tricarbonyl pointed to the possibility complexes of other organic ligands that are elusive in their free state. Trimethylenemethane (TMM) has a natural connection to cyclobutadiene, and, in 1966, Emerson and co-workers reported the first trimethylenemethane (TMM) transition metal complex, (CO)3FeC(CH2)3, which became the starting point for extensive studies.
Generally speaking, trimethylenemethane complexes are synthesized in the following four ways: (A) the dehalogenation of α, α'-dihalosubstituted precursors, (B) the thermal extrusion of XY (XY = HCl, Br2, and CH4,) from η3-methylallyl complexes, (C) the ring opening of alkylidenecyclopropanes, and (D) the elimination of Me3SiX [X = OAc, Cl, OS(O)2Me] from functionalized allylsilanes (Figure 1).
η4-[C(CH2)3]Fe(CO)3, the first trimethylenemethane metal complex to be reported, was obtained from the reaction of 3-chloro-2-chloromethylprop-1-ene with Fe2(CO)9 or Na2[Fe(CO)4]. [2] Followed by this result, a number of substituted trimethylenemethane iron complexes have been prepared. [3] [4] [5]
The thermal extrusion from η3-methylallyl complexes was reported by Emerson.The iron allyl complex, obtained from the reaction of 3-chloro-2-methylprop-1-ene with [Fe2(CO)9], decomposed on heating to afford the iron trimethylenemethane complex. [6]
In the presence of [Fe2(CO)9], the ring opening of 2-substituted methylenecyclopropanes leads to the formation of various η4-trimethylenemethane complexes containing different functional groups, such as (R1 = H, R2 = Ph), (R1 = Me, R2 = Ph), (R1 = R2 = Ph), and (R1 = H, R2 = CH=CH2). [8] The stereochemistry has been elucidated by deuterium-labeling experiments.
[[Pd(PPh3)4]] is a precursor to highly reactive η3-trimethylenemethane complexes. [1] Allylsilanes oxidatively add to some low-valent d8 complexes resulting in the formation of an η1-allyl complexes, followed by the formation of an η3-allyl complex, and finally elimination of Me3SiX to yield the η4-trimethylenemethane complex. The isolation of the proposed intermidate further confirmed the mechanism. [9]
According to gas phase electron diffraction, η4-C(CH2)3]Fe(CO)3 adopts a staggered conformation about the iron center. The ligands, which include carbonyl and a trigonal-pyramidal trimethylenemethane, are arranged in the usual umbrella-type configuration. The central carbon of the trimethylenemethane ligand is closer to the iron center compared to the outer methylene carbons. This was confirmed by the Fe-C(central) distance measuring 1.94(1) Å, while the Fe-CH distances were measured at 2.12 Å. [10] Moreover, this result has also been confirmed by X-ray diffraction and vibrational spectrum. [11]
The primary bonding interaction occurs between the 2e set of the Fe(CO)3 fragment and e" on the trimethylenemethane ligand. However, if the metal-trimethylenemethane axis is rotated by 60° into an eclipsed geometry, the interaction between 2e and e" is minimized, which results in an increase in the energy of the HOMO in the complex, which is a significant factor that provides a barrier to rotation, as shown in Figure 6b.
Extended Huckel calculations give a barrier of 87 KJ mol−1 using a planar trimethylenemethane ligand. [12] Introducing a puckered conformation to the trimethylenemethane ligand, which resembles the experimental geometry, leads to an increase in the calculated barrier to 98.6 kJ mol−1. This puckering induces mixing of s character into e" orbitals, causing a more pronounced orientation toward the metal center. Consequently, the overlap between e" and 2e orbitals is enhanced. The degree of puckering, characterized by θ, falls within the range of 12°. [13] The mixing of s character into e" also results in the H-C-H plane being tipped away from the metal. The angle β, between C-1 and C-2 and the plane H-C-H, is typically about 15°.
Trimethylenemethane complexes undergo a wide variety of reactions including those with electrophiles, nucleophiles as well as redox reactions.
η4-C(CH2)3]Fe(CO)3 adds hydrogen chloride to yield η3-CH3C(CH2)]Fe(CO)3. Substituted trimethylenemethane iron complexes, on the other hand, react with strong acids to produce cross-conjugated dienyl iron cations and η4-diene complexes. [14] η4-C(CH2)3]Mo(CO)2(C5H5)+ add nucleophiles to give charge-neutral η3-allyl complexes. [15]
[Fe{η4-C(CH2)3(L)3] (L = PMe or PMe2Ph) (complex 4) reacts with silver trifluoromethanesulfonate to give the 17-electron cation (Figure 7). [16]
The Pauson–Khand (PK) reaction is a chemical reaction, described as a [2+2+1] cycloaddition. In it, an alkyne, an alkene and carbon monoxide combine into a α,β-cyclopentenone in the presence of a metal-carbonyl catalyst.
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium, tungsten, and seaborgium analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.
Chromium hexacarbonyl is a chromium(0) organometallic compound with the formula Cr(CO)6. It is a homoleptic complex, which means that all the ligands are identical. It is a colorless crystalline air-stable solid, with a high vapor pressure.
In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.
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Diiron nonacarbonyl is an organometallic compound with the formula Fe2(CO)9. This metal carbonyl is an important reagent in organometallic chemistry and of occasional use in organic synthesis. It is a more reactive source of Fe(0) than Fe(CO)5. This micaceous orange solid is virtually insoluble in all common solvents.
Dimanganese decacarbonyl, which has the chemical formula Mn2(CO)10, is a binary bimetallic carbonyl complex centered around the first row transition metal manganese. The first reported synthesis of Mn2(CO)10 was in 1954 at Linde Air Products Company and was performed by Brimm, Lynch, and Sesny. Their hypothesis about, and synthesis of, dimanganese decacarbonyl was fundamentally guided by the previously known dirhenium decacarbonyl (Re2(CO)10), the heavy atom analogue of Mn2(CO)10. Since its first synthesis, Mn2(CO)10 has been use sparingly as a reagent in the synthesis of other chemical species, but has found the most use as a simple system on which to study fundamental chemical and physical phenomena, most notably, the metal-metal bond. Dimanganese decacarbonyl is also used as a classic example to reinforce fundamental topics in organometallic chemistry like d-electron count, the 18-electron rule, oxidation state, valency, and the isolobal analogy.
Transition metal dinitrogen complexes are coordination compounds that contain transition metals as ion centers the dinitrogen molecules (N2) as ligands.
In organometallic chemistry, a transition metal indenyl complex is a coordination compound that contains one or more indenyl ligands. The indenyl ligand is formally the anion derived from deprotonation of indene. The η5-indenyl ligand is related to the η5cyclopentadienyl anion (Cp), thus indenyl analogues of many cyclopentadienyl complexes are known. Indenyl ligands lack the 5-fold symmetry of Cp, so they exhibit more complicated geometries. Furthermore, some indenyl complexes also exist with only η3-bonding mode. The η5- and η3-bonding modes sometimes interconvert.
Organoiron chemistry is the chemistry of iron compounds containing a carbon-to-iron chemical bond. Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate. While iron adopts oxidation states from Fe(−II) through to Fe(VII), Fe(IV) is the highest established oxidation state for organoiron species. Although iron is generally less active in many catalytic applications, it is less expensive and "greener" than other metals. Organoiron compounds feature a wide range of ligands that support the Fe-C bond; as with other organometals, these supporting ligands prominently include phosphines, carbon monoxide, and cyclopentadienyl, but hard ligands such as amines are employed as well.
Transition metal carbyne complexes are organometallic compounds with a triple bond between carbon and the transition metal. This triple bond consists of a σ-bond and two π-bonds. The HOMO of the carbyne ligand interacts with the LUMO of the metal to create the σ-bond. The two π-bonds are formed when the two HOMO orbitals of the metal back-donate to the LUMO of the carbyne. They are also called metal alkylidynes—the carbon is a carbyne ligand. Such compounds are useful in organic synthesis of alkynes and nitriles. They have been the focus on much fundamental research.
Metal carbon dioxide complexes are coordination complexes that contain carbon dioxide ligands. Aside from the fundamental interest in the coordination chemistry of simple molecules, studies in this field are motivated by the possibility that transition metals might catalyze useful transformations of CO2. This research is relevant both to organic synthesis and to the production of "solar fuels" that would avoid the use of petroleum-based fuels.
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Cyclopentadienyliron dicarbonyl dimer is an organometallic compound with the formula [(η5-C5H5)Fe(CO)2]2, often abbreviated to Cp2Fe2(CO)4, [CpFe(CO)2]2 or even Fp2, with the colloquial name "fip dimer". It is a dark reddish-purple crystalline solid, which is readily soluble in moderately polar organic solvents such as chloroform and pyridine, but less soluble in carbon tetrachloride and carbon disulfide. Cp2Fe2(CO)4 is insoluble in but stable toward water. Cp2Fe2(CO)4 is reasonably stable to storage under air and serves as a convenient starting material for accessing other Fp (CpFe(CO)2) derivatives (described below).
Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usually described as two equivalent resonance structures.
Lisa McElwee-White is currently the Colonel Allen R. and Margaret G. Crow Professor of Chemistry at the University of Florida.
Phosphenium ions, not to be confused with phosphonium or phosphirenium, are divalent cations of phosphorus of the form [PR2]+. Phosphenium ions have long been proposed as reaction intermediates.
Vinylcyclopropane [5+2] cycloaddition is a type of cycloaddition between a vinylcyclopropane (VCP) and an olefin or alkyne to form a seven-membered ring.
A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P−) is comparable to an amido anion (R2N−), except that the M-P distances are longer and the phosphorus atom is more sterically accessible. For these reasons, phosphido is often a bridging ligand. The -PH2 ion or ligand is also called phosphanide or phosphido ligand.
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.