A metallacarboxylic acid is a

metal complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

with the ligand CO₂H. These compounds are intermediates in reactions that involve

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

, these species are intermediates in the

water gas shift reaction Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...

. Metallacarboxylic acids are also called hydroxycarbonyls.

Preparation

Metallacarboxylic acids mainly arise by the attack of

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

on electrophilic metal carbonyl complexes. An illustrative synthesis is the reaction of a cationic iron carbonyl with a stoichiometric amount of base: : C₅H₅)(CO)₂FeCOF₄ + NaOH → [(C₅H₅)(CO)₂FeCO₂H + NaBF₄ When applied to simple metal carbonyls, this kind of conversion is sometimes called the Hieber base reaction. Decarboxylation of the resulting anion gives the anionic hydride complex. This conversion is illustrated by the synthesis of Iron tetracarbonyl hydride, [HFe(CO)₄]⁻ from iron pentacarbonyl. :Fe(CO)₅ + NaOH → NaFe(CO)₄CO₂H :NaFe(CO)₄CO₂H → NaHFe(CO)₄ + CO₂

Related compounds

Metallacarboxylic acids exist in equilibria with the carboxylate anions, L_nMCO₂⁻. Metallacarboxylate esters (L_nMCO₂R) arise by the addition of alkoxide to metal carbonyl: : _nM-COsup>+ + ROH → _nM-CO₂R+ H⁺ Metallacarboxylic amides (L_nMC(O)NR₂) arise by the addition of amide to metal carbonyl: : _nM-COsup>+ + 2 RNH₂ → _nM-C(O)N(H)R+ RNH₃⁺ Derivatives of metalla''dithia''carboxylic acids are also known. They are prepared by treating anionic complexes with

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical n ...

.{{cite journal , last1 = Dombek , first1 = R. Duane , last2 = Angelici , first2 = Robert J. , year = 1977 , title = Dicarbonyl(η5-Cyclopentadienylxthio-Carbonyl)Iron(1 +) Hexafluorophosphate(1 -) and Dicarbonyl(η 5-Cyclopentadienyl)- Methylthio)Thiocarbonylron , journal = Inorganic Syntheses , volume = 17 , page = 100ff , doi = 10.1002/9780470132487.ch29 , isbn = 9780470132487

References

Carbonyl complexes Organometallic chemistry Transition metals