In organometallic chemistry, a transition metal formyl complex is a metal complex containing one (usually) or more formyl (CHO) ligand. A subset of

transition metal acyl complexes Transition metal acyl complexes describes organometallic complexes containing one or more acyl (RCO) ligands. Such compounds occur as transient intermediates in many industrially useful reactions, especially carbonylations. Structure and bonding ...

, formyl complexes can be viewed as metalla-aldehydes. A representative example is (CO)₅ReCHO. The formyl is viewed as an X (pseudohalide) ligand. Metal formyls are proposed as intermediates in the hydrogenation of

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 si ...

, as occurs in the Fischer-Tropsch process.

Structure and bonding

The MCHO group is planar. A C=O

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

is indicated by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...

. A second resonance structure has a M=C double bond, with negative charge on oxygen.

Synthesis and reactions

Metal formyl complexes are often prepared by the reaction of metal carbonyls with hydride reagents: : e(CO)₆sup>+ + H⁻ → (CO)₅ReCHO The CO ligand is the electrophile and the hydride (provided typically from a

borohydride Borohydride refers to the anion , which is also called tetrahydroborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing , where ''n'' is an integer from 0 to 3, for example cyanoborohydride or cyanotrihyd ...

) is the nucleophile. Some metal formyls are produced by reaction of metal carbonyl anions with reagents that donate the equivalent of a formyl cation, such a mixed formate anhydrides. Metal formyls participate in many reactions, many of which are motivated by interest in Fischer-Tropsch chemistry. O-alkylation gives carbenoid complexes. The formyl ligand also functions as a base, allowing the formation of M-CH=O-M' linkages. Decarbonylation leads to de-insertion of the carbonyl, yielding hydride complexes.

References

{{Coordination complexes Organometallic chemistry Transition metals Coordination chemistry