Talk:Grignard reagent

How important is the complexing with the solvent?

Several Wikipedia articles about Grignard reagents seem a bit too focused on the fact that the reagents in solution are complexated by the ethereal solvents. The original version of this article dwelt on that point even before explaining what a GR is, and what it is used for; and the first image offered is of the complex with THF, that does not help at all the reader who wants to understand what a GR is.
But how important is that fact, anyway? Can't the Grignard reactions be understood without reference to those ligands? Do they take any part in the reaction (other than making the reagent soluble)?
Elsewhere I read that the GRs can be extracted as solids (although no one would want to do that, it seems). Are the Mg atoms in those solids complexated too?
In high school we learn that CuSO₄ and NaOH dissolved in water split into ions Cu²⁺, SO2−4, Na⁺, and HO⁻; and that is enough to understand what happens when the two solutions are mixed. Actually the Cu²⁺ ions are complexated with water, but that does noy matter for that level of understanding. Isn't this also the case with GR-solvent interactions? --Jorge Stolfi (talk) 05:55, 2 April 2019 (UTC)

Good questions. 99.99% of GR chemistry involves its adducts, explicitly (crystallography) or implicitly (the reaction solvent). Probably some specialized work has devised a way to make solvent free GR's. The ether ligands probably exchange readily, allowing binding of, say, ketones, which allows the Grignard reaction to occur.

CuSO₄ when "dissolved" does not split into ions. First it becomes the hydrate, probably a solid state reaction, which disconnects the Cu-OSO-Cu linkages. THEN the hydrate dissolves. But you seem to understand that. --Smokefoot (talk) 11:11, 3 April 2019 (UTC)

Search of Cambridge X-ray database shows 70+ structures with C-Mg-Br connectivity. Most are dietherates. Some mono-ether complexes with bridging halides. Some amine complexes (2 amines in place of 2 ether). This paper DOI 10.1016/S0022-328X(00)80080-7 described MeMgBr(THF)3, with pentacoordinated Mg. Several complexes with chelating di- and tri-ethers, some even with octahedral Mg. The neopentyl bromide has been obtained solvent-free Me3CCH2MgBr: it is a polymer with bridging alkyls and bridging bromides (doi:10.1016/0022-328X(89)85078-8).

The GR situation is a little like the copper sulfate situation. Sure, there is anhydrous copper(II) sulfate, but it is an oddity that is almost totally useless except for archane discussions (and Wikipedia). Sure, one could get solvent free GR in some special substituents, but they adopt polymeric structures (see trimethylaluminium) and it is unclear that their reactivity resembles that of normal RMgX(etherate)2.--Smokefoot (talk) 11:25, 3 April 2019 (UTC)

Thanks! But I was more interested in my first two questions. When thinking about Grignard reactions, is it important to know that the Mg is coordinated to those two solvent molecules?
Much of the chemistry of Cu(2+) in solution, like Cu²⁺ + Fe → Cu + Fe²⁺ can be understood without thinking about the six H₂O that are always attached to it. Isn't that the case with the GRs too? The solvent molecules are important to explain why it is dissolved at all, but they do not seem to take (visible) part in the reactions. The latter seem to involve the R−Mg bond in the GR, and the bonds on or near the affected carbons in R and the "substrate". The solvent molecules are just pushed aside during the reaction. Isn't that so?
--Jorge Stolfi (talk) 14:37, 3 April 2019 (UTC)

PS. By the way, anhydrous copper sulfate seems to be the standard high school demonstration of "water of hydration". I did it a few times myself as a teenager. And I recall someone proposing to use it as a way to dry ethanol or other solvents (instead of Mg or Na sulfate, Na carbonate, etc.). --Jorge Stolfi (talk) 14:49, 3 April 2019 (UTC)

PPS. Youtuber NurdRage has spent the last few months perfecting a reaction that produces sodium metal from magnesium metal and NaOH in mineral oil, with a tertiary alcohol as a catalyst. I did not quite understand the proposed mechanism (and he is not sure either), but it apparently involves some organic Mg compound that is soluble in mineral oil. (It could be instead sodium alkoxide that reacts with Mg metal, but then the sodium should remain attached to the Mg, which does not seem to be the case...) Any idea of what it could be? There seem to be no halides in that system, nor ether oxygens in the solvent... --Jorge Stolfi (talk) 14:49, 3 April 2019 (UTC)

'is it important to know that the Mg is coordinated to those two solvent molecules?" Define "important"? Organic textbooks do not bother to mention the coordinated ethers. So from that perspective the ethers are unimportant.

"Much of the chemistry of Cu(2+) in solution, like Cu²⁺ + Fe → Cu + Fe²⁺ can be understood without thinking about the six H₂O that are always attached to it." I guess at some very primitive level. But for weighing reagents, discussing mechanisms, planning syntheses,... knowledge of the first coordination sphere is essential. It separates the enlightened from the Neanderthals (IMHO).

"The solvent molecules are important to explain why it is dissolved at all, but they do not seem to take (visible) part in the reactions." Sure. that is the reason we omit the ether in textbooks. (Water is a far more complicated ligand).

"it apparently involves some organic Mg compound that is soluble in mineral oil." probably Mg(OBut)2.

"anhydrous copper sulfate seems to be the standard high school demonstration of "water of hydration"." yes, a nice color change with cheap, safe compound. Very complicated process. But everyone likes color changes (me too). Another interesting demonstration is the use of (hydrated) chromous chloride on the dissolution of anhydrous chromic chloride in water. --Smokefoot (talk) 18:26, 3 April 2019 (UTC)

Just a reminder. This article is about the reagents and not the reaction. I.e. there should be an inorganic perspective too. The Grignard reaction do not talk much about the "solvent". Inorganic textbooks, like Housecrofts and Chemistry of the Elements discuss the topic (the latter uses five pages). They write about the structure, and crystal structures, and the solvent versus equllibrium (Schlenk eq. and related)

re: Smokefoot: "Organic textbooks do not bother to mention the coordinated ethers." Sundberg and Carey, Advanced organic chemistry describes the solvent, the Schlenk equilibrium and has a crystal structure too. Christian75 (talk) 20:28, 3 April 2019 (UTC)

OK thanks for the tips. I should say, organic textbooks do not indicate ether solvents in equations for Grignard reagents. Please feel free to edit if you see anything problematic.--Smokefoot (talk) 07:14, 4 April 2019 (UTC)

"probably Mg(OBut)2." I thought of that... But the Mg in it is fully oxidized, right? I don't see how it could react with (anhydrous solid) NaOH to reduce the sodium and regenerate the HOBut.
Maybe it is But-O-Mg-H instead? Would that qualify as a Grignard reagent? (Isn't hydrogen the Neanderthal of the halogens? 😀) Or maybe But-O-Mg-Mg-O-But? --Jorge Stolfi (talk) 13:21, 4 April 2019 (UTC)

Your guesses seem good to me.--Smokefoot (talk) 17:52, 4 April 2019 (UTC)

• OK, so here is a question that DOES belong in this talk page 😀: is hydrogen a valid "X" for the concept of Grignard reagent? Do such compounds exist, and are they used?
  All the best, --Jorge Stolfi (talk) 06:07, 5 April 2019 (UTC)

It seems "RMgH" compounds are irrelevant to the topic of Grignard reagents, IMHO. OrganoMg chemistry appears to be pretty vast. I am no expert though. Wikipedia is about mainstream, but the weirdos, again IMHO.--Smokefoot (talk) 00:17, 6 April 2019 (UTC)

CH2=CHCH2Br+Mg will give grignard reagent?

Can bromo prop 1ene react with magnesium and give grignard reagent as a product? 106.66.19.48 (talk) 13:45, 30 July 2022 (UTC)

Grignard reagent

Kannada 2405:201:D014:7D98:6D6B:DA32:119D:2A6A (talk) 15:04, 2 September 2022 (UTC)