Application of hydrides as reductants for coordinated carbonyl ligands

3 Application of hydrides as reductants for coordinated carbonyl ligands 

The structure clearly shows the presence of mutually trans carbonyl and formyl groups, the two being easily distinguished by an Os-C-O angle of 

7° for the formyl ligand. The formyl hydrogen was not located in the X-ray structure, but the presence of a formyl group was verified by IR and NMR methods.  

In many cases, the synthesis of formyl complexes is performed in tetrahydrofuran using strong monohydride donors, typically alkali metal trialkylborohydrides. Although LiLBHEtsl is commonly employed in preparative coordination chemistry, it is not always possible to convert carbonyl complexes into formyl complexes with this reagent. In such cases a stronger hydride donor, such as K[BH(Bu-sec)3l, is required. 9 

Many formyl complexes are thermally unstable (vide supra), and, therefore, the separation of trialkylborane by-products of low volatility from a reaction mixture can be problematic. In such cases, formyl complexes are generally produced and studied in situ. 

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