chemistry

Organomanganese chemistry

Organomanganese chemistry is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Organomanganese chemistry rather than just read about it. In short: Organomanganese chemistry is the chemistry of organometallic compounds containing a carbon to manganese chemical bond. In a 2009 review, Cahiez et al. argued that as manganese is cheap and benign (only iron performs better in these aspects), organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.

Key takeaways

Organomanganese chemistry belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Organomanganese chemistry to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Organomanganese chemistry from memory before moving on to harder problems.

Reference excerpt

Organomanganese chemistry is the chemistry of organometallic compounds containing a carbon to manganese chemical bond. In a 2009 review, Cahiez et al. argued that as manganese is cheap and benign (only iron performs better in these aspects), organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.

Synthesis Organomanganese compounds were first reported in 1937 by Gilman and Bailee who described the reaction of phenyllithium and manganese(II) iodide to form phenylmanganese iodide (PhMnI) and diphenylmanganese (Ph2Mn). Following this precedent, other organomanganese halides can be obtained by alkylation of manganese(II) chloride, manganese(II) bromide, and manganese(II) iodide. Manganese iodide is attractive because the anhydrous compound can be prepared in situ from manganese and iodine in ether. Typical alkylating agents are organolithium or organomagnesium compounds:

RM + MnX2→ 2RMnX + MX 2RM + MnX2→ R2Mn + 2MX A variety of organomanganates (the ate complex) are isolable:

3RM + MnX2→ R3MnX + 2MX 4RM + MnX2→ R4MnX2+ 2MX The organomanganese compounds are usually prepared in THF where they are the most stable (via complexation) even though many of them must be handled at low temperatures. Simple dialkylmanganese compounds decompose by beta-hydride elimination to a mixture of alkanes and alkenes.

Derivatives of Mn2(CO)10 Many organomanganese complexes are derived from dimanganese decacarbonyl, Mn2(CO)10. Bromination and reduction with lithium affords BrMn(CO)5 and LiMn(CO)5, respectfully. These species are precursors to alkyl, aryl, and acyl derivatives:

BrMn(CO)5 + RLi → RMn(CO)5 + LiBr LiMn(CO)5 + RC(O)Cl → RC(O)Mn(CO)5 + LiCl RMn(CO)5 + CO → RC(O)Mn(CO)5 The general pattern of reactivity is analogous to that for the more popular cyclopentadienyliron dicarbonyl dimer. The Mn(I) compound BrMn(CO)5 is also the precursor to many pi-arene complexes:

BrMn(CO)5 + Ag+ + C6R6 → [Mn(CO)3(C6R6)]+ + AgBr + 2 CO These cationic half-sandwich complexes are susceptible to nucleophilic additions to give cyclohexadienyl derivatives and ultimated functionalized arenes.

Reactions The chemistry of organometallic compounds of Mn(II) are unusual among the transition metals due to the high ionic character of the Mn(II)-C bond. The reactivity of organomanganese compounds can be compared to that of organomagnesium and organozinc compounds. The electronegativity of Mn (1.55) is comparable to that of Mg (1.31) and Zn (1.65), making the carbon atom (EN = 2.55) nucleophilic. The reduction potential of Mn is also intermediate between Mg and Zn. Organomanganese halides react with aldehydes and ketones to the alcohol, with carbon dioxide to the carboxylic acid (tolerating higher operating temperature than corresponding RLi or RMgBr counterparts), sulfur dioxide and isocyanates behaving like soft Grignard reagents. They do not react with esters, nitriles, or amides. They are more sensitive to steric than to electronic effects. With acyl halides RMnX compounds form the corresponding ketones. This reaction is chemoselective and has been applied in organic synthesis for this reason. Certain manganese amides of the type RR1NMnR2 are used for the deprotonation of ketones forming manganese enolates. Just like lithium enolates they can further react with silyl chlorides to silyl enol ethers, with alkyl halides in alpha-alkylation and with aldehydes and ketones to beta-keto-alcohols. Manganese enolates can also be obtained by transmetalation of manganese halides with Li, Mg, K or Na enolates. Manganese halides are catalysts in several homo- and crosscoupling reactions involving stannanes and Grignards in which organomanganese intermediates play a part. Likewise coupling reactions involving organomanganese halides are catalysed by Pd, Ni, Cu and Fe compounds. Manganese chloride is a precursor to organomanganese reagents in organic chemistry.

Activated manganese Commercial manganese powder is not suited for the synthesis of organomanganese compounds. In 1996 Rieke introduced activated manganese (see Rieke metal) obtained by reaction of anhydrous manganese(II) chloride with lithium metal in a solution of a catalytic amount of naphthalene in THF. Other reducing agents are potassium graphite and magnesium. Activated manganese facilitates the Mn version of the Barbier reaction and the pinacol coupling.

High-valent compounds Several organomanganese compounds with valency +3 or +4 are known. The first one discovered (1972) was Mn(nor)4 with four norbornyl units. An octahedral [MnIVMe6]−2 complex was reported in 1992, obtained by reaction of MnMe4(PMe3), with methyllithium followed by addition of TMED.

Worked examples

Example 1 — a first encounter with Organomanganese chemistry

Start with the simplest possible case. Write down what Organomanganese chemistry claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Organomanganese chemistry before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Organomanganese chemistry ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Organomanganese chemistry

In research: Organomanganese chemistry appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Organomanganese chemistry in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Organomanganese chemistry is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organomanganese compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Organomanganese chemistry outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Organomanganese chemistry in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Organomanganese chemistry means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Organomanganese chemistry out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Organomanganese chemistry in simple terms?

Why does Organomanganese chemistry matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Organomanganese chemistry?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Organomanganese chemistry.