Tag Info

17

The "real" structure of ferrocene is an iron atom sandwiched between two flat, parallel, pentagonal C5H5 rings. The diagram above shows the atomic positions from a crystal structure but the bonds are merely a convenience and don't accurately summarize the way the bonding works though the picture does accurately summarize the atomic positions in the ...

15

I am not sure if Silane ($\ce{SiH_4}$) can really be considered. But there are silicides which silicon forms with strongly electropositive metals. In these compounds, silicon has a negative oxidation state. For magnesium silicide - $\ce{Mg_2Si}$, the oxidation state of silicon would be -4.

13

It seems like an idea of using magnesium anthracene systems for the $\ce{MgH2}$ production persisted since 1980s [1] till late 2000s, when new more efficient method with better scalability for industrial use was established. One of the recent reviews in hydrogen-storage applications [2, p. 220] compares the older two-step process of $\ce{MgH2}$ synthesis: ...

12

You are correct. Grignard reagents $\ce{RMgX}$ (where $\ce{R}$ stands for some hydrocarbon group and $\ce{X}$ is a halogen, usually $\ce{Cl}$, $\ce{Br}$, or $\ce{I}$) react with carbon dioxide to produce carboxylic acids after acidic workup: $$\ce{RMgX ->[1)\ \ce{ CO2}][2)\ \ce{ H3O+}] RCO2H}$$ $$\ce{RMgX + CO2 -> RCO2- MgX+}$$ $$\ce{RCO2- + H3O+ -&... 12 Huy Ngo says it all. A Grignard reageant will react first with just about any hydrogen that has even a modicum of proton donation capability, before "resorting" to the slower nucleophilic attack. To get a ketone (in most cases), avoid the dissociable proton by using a nitrile instead, assisted by a copper salt. This forms an intermediate imine ... 11 The difference in electronegativity between copper (1.9) and magnesium (1.3) is the key difference. Since copper is more electronegative than magnesium its electronegativity is much closer to that of carbon (2.55). This results in carbon-copper bonds being less polarized and more covalent than carbon-magnesium bonds. The electrons in a carbon-copper ... 10 Yes there are, many in fact. One of the examples is having a complex consisting of a fluorene molecule and of cp altogether with iron, described by Decken in Acta Cryst. E (doi: 10.1107/S1600536804028077): (source) You are not limited to complexation with iron, though. Already by the title «Synthesis and characterisation of Ti, Cr, Mo and W bis(fluorene) ... 8 Organotin compounds are rather toxic. They are also persistent in the environment and have a long biological half-life. The problem is that trialkyltin byproducts from your reaction are difficult to separate from the product. In the lab, this is painful and (usually) involves multiple columns, but when you want to get a drug past the FDA into the clinic ... 8 How Did Wittig Come to Discover Lithium-Halogen-Exchange? Georg Wittig, discoverer of the Wittig reaction, was studying the effect of ring strain on the strength of two neighboring carbons; by adding enough strain he expected to coax C-C bonds into forming diradicals: Unfortunately tetraphenylbenzocyclobutane rearranges to triphenyldihydroanthrancene ... 8 Copper is used to avoid lithium-halogen exchange. Additional information on that reaction can be found in this discussion. Organolithiums will often, instead of acting as a nucleophile, form a new organolithium:$$\ce{RLi + R'X <=> RX + R'Li} Using $\ce{Cu(I)}$ allows the formation of an organocuprate, which acts as a nucleophile, allowing alkylation ...

8

The IUPAC Goldbook provides no 'official' definition of the term heteroatom,and as such you're somewhat free to use (and abuse) the term as you see fit. Since no IUPAC definition exists, it may be helpful for you to define what you plan on calling a heteroatom at the beginning of whatever you're writing, to inform the reader (common practice in scientific ...

7

The difference between THF and epoxides is perhapse bigger than you might think. Due to the three-membered-ring of an epoxide, a lot of energy is 'stored' in ring strain. This destabilizes the stucture and is a driving force for a Grignard reaction (or any substitution on an epoxide). The THF is a five-membered-ring, which is far more stable. This bond is ...

7

As a result of the -I effect of the trifluoromethyl group, triflate is a better nucleofuge than mesylate and tosylate. As compared to tosylate and nosylate, triflate is rather small. This might be an advantage in reactions at "crowded" centres. Triflates do not undergo side reactions, such as hydrogen abstraction reactions, etc. A triflate, once ...

7

TL; DR: coordination number of carbon atom in methyllithium tetramer is indeed 7, arising from 6 intramolecular interactions, as you suggested, and an extra bond with the lithium atom of the next tetramer. The key point is that you need to look beyond the tetramer. I'm sorry to inform you that the image from Wikipedia of the standalone cubane $\ce{Li4(CH3)4}... 7 It was a great effort. However, in the proposed name bis[(μ-2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl-1κC1,2κC7)chromium](5 Cr—Cr) I can see several issues: In you point 12: Forcing the metal-metal bond multiplicty in the name is interesting, however I wouldn't go against the rules. See the example with the multiple (triple) Cr-Cr bond, in the ... 7 @tox123: You have generated two radicals on the same carbon by a two-electron reductive α-elimination (1 --> 2). So far, so good. In other words, you have created a carbene (2). Carbenes can rearrange to alkenes, NOT alkynes. Think of the two orbitals on the carbenoid carbon as one bearing two-electrons (negative) and the other one vacant (positive) (3)... 7 Nicco: Of course you can't "see it". If you were given the correct structure, the solution to your post would be straightforward. There should be a double bond in the lactam ring as shown in compound 1. The reaction is conducted in acetonitrile (bp. 82oC) at reflux. These conditions allow for a Claisen rearrangement to occur to form ketolactam 2. Subsequent ... 7 As one might expect for an element with no long-lived isotopes, little is known about organopolonium compounds. What is known may be broadly divided into two categories [1,2; cited by Wikipedia]: Compounds where polonium takes the place of a lighter chalcogen, acting more nearly parallel to sulfur, selenium and tellurium than to oxygen. Examples include ... 7 To get the gravity of how toxic organotin compounds can be, let us compare it with inorganic tin compounds. Most of the inorganotin compounds are non-toxic because of their low solubility and low absorption in human body. Workers mining tin oxide suffer from "stannosis", a benign form of pneumoconiosis without any tissue reaction or harmful ... 6 If this is in regard to mechanisms with organometallic complexes or coordination compounds, there are a set of specific mechanisms that are well defined. These are: Ligand dissociation / association Reductive elimination / oxidative addition Intramolecular insertion (e.g. CO migratory insertion) / elimination (e.g.$\beta$–hydride elimination) Metallacycle ... 6 Unfortunately, you don't give an indication of what you expect the chemical shift for the -Me to be, other than higher than is observed. However, you are correct in your assumption; the π back donation from the Mn centre to CO ligands does decrease the shielding, and therefore does increase the chemical shift, but this is a good case of how chemical ... 6 I think your suggestion about the stability of the tetrahedral intermediate is correct, but it's not that the tetrahedral intermediate itself has stability. I think it's because the collapse of the tetrahedral intermediate leads to a less stable intermediate. My key insight for rationalizing this is that lithium hydride reduction of amides generally affords ... 6 The text box you are quoting from (p 219) refers to this specific reaction. The compound in question possesses an α-hydroxyl group, which needs to be deprotonated too. Notice that three equivalents of organolithium are needed in this reaction: one to deprotonate the acid, one to deprotonate the hydroxyl group, and one to react with the lithium carboxylate. ... 6 Let's look at the molecular orbital diagram calculated with JSmol. As you know, the principal effect is back-donation from the metal to the π-antibonding orbitals of the carbon monoxide. But not all 3d transition metals are created equal. Earlier ones like titanium, with lower electronegativity and lower ionization energy, are better at this back-donation ... 5 A Grignard reagent is an organomagnesium halide of the generic form$\ce{RMgX}$, where$\ce{R}$is a hydrocarbon group and$\ce{X}$is a halide, usually$\ce{Cl}$,$\ce{Br}$, or$\ce{I}$. These reagents are produced by the reaction of magnesium metal with the corresponding organic halide in a non-protic (but coordinating) solvent, like diethyl ether. For ... 5 Reaction of a Grignard reagent with an ester is a standard method for producing tertiary alcohols where at least two of the substituents (the "$\small\ce{R_2}$" group attached to the Grignard) are the same. Judicious choice of the starting ester allows for the preparation of a tertiary alcohol where all 3 substituents are the same. Alternately, you could ... 5 I appreciate the suggestions but some digging found a few possibilities: As I mentioned in the question, there's the Cambridge Structural Database, which includes over 700,000 compounds (both organic and inorganic/organometallic). It's decidedly not free, but available at many universities. There is the "Teaching Subset" of 733 compounds from CCDC which ... 5 I don't remember a direct palladation of arylboronic acids or their derivatives in any of the couplings. Typically,$\ce{Pd(0)}$inserts into the$\ce{C-Hal}$bond of arylhalides and is thus oxidized to$\ce{Pd(II)}$. Ouite often,$\ce{Hal}$is then displaced with$\ce{OR}$by the action of a base. Think in$\ce{KOt-Bu}\$ often used in the Kumada coupling. ...

5

Technically, you are comparing apples and oranges. Grignards and organolithium compounds are good nucleophiles (with the caveat permeakra highlighted) towards carbonyl groups. But they cannot attack alcohols, water, amines or alkynes nucleophilicly. There is simply no attack mechanism possible that would result in a more stable addition product. In fact, ...

5

Coordinated benzene as a dienophile It would be logical to suggest that an η4-benzene ligand could behave as a dienophile. The reason why benzene is characteristically unreactive, both as a dienophile and as a diene, is because of its aromaticity; if aromaticity is lost, one would expect it to become more reactive. However, to the best of my knowledge (and ...

Only top voted, non community-wiki answers of a minimum length are eligible