Transition metal formyl complex
In organometallic chemistry, a transition metal formyl complex is a metal complex containing one or more formyl ligand. A subset of transition metal acyl complexes, formyl complexes can be viewed as metalla-aldehydes. A representative example is 5ReCHO. The formyl is viewed as an X ligand. Metal formyls are proposed as intermediates in the hydrogenation of carbon monoxide, as occurs in the Fischer-Tropsch process.
Structure and bonding
The MCHO group is planar. A C=O double bond is indicated by X-ray crystallography. 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:The CO ligand is the electrophile and the hydride 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.