Osmium complexes formyls

Roper has been able to isolate another osmium formyl by rearrangement of an rj2-formaldehyde complex, as shown in Eq. (9) (54). Because of the unavailability of such precursors, this reaction also does not provide a general entry into neutral formyl complexes. However, Eq. (9) does lend support to the claim that the related ruthenium formyl, Ru(H)(solv) (PPh3)3(CHO) (40), can be isolated as an impure solid, contaminated with substantial quantities of an rf -formaldehyde precursor (55). 

Neutral formyl complexes which contain ligating CO often decompose by decarbonylation however, several exceptions exist. For instance, the osmium formyl hydride Os(H)(CO)2(PPh3)2(CHO) evolves H2(54). Although the data are preliminary, the cationic iridium formyl hydride 49 [Eq. (14)] may also decompose by H2 evolution (67). These reactions have some precedent in earlier studies by Norton (87), who obtained evidence for rapid alkane elimination from osmium acyl hydride intermediates Os(H)(CO)3(L)(COR) [L = PPh3, P(C2H5)3], Additional neutral formyls which do not give detectable metal hydride decomposition products have been noted (57, 65) however, in certain cases this can be attributed to the instability of the anticipated hydride under the reaction conditions (H2 loss or reaction with halogenated solvents). 

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