Alkyl phosphites, transition metal

The complex of tartaric acid and antimony (emetic) was described three centuries ago. Nevertheless, the structure of this compound has been elucidated these last fifteen years by X-ray diffraction ( 1 ). In fact, emetic presents a binuclear cyclic structure. Many authors mentioned similar complex with transition metals (vanadium (2), chromium (3)) or metalloids (arsenic (4), bismuth (5)). Emetic with phosphorus was not mentioned. Nevertheless, tartaric acid or alkyl tartrates has been utilized in phosphorus chemistry tartaric acid reacts with trialkyl phosphites giving heterocyclic phosphites (6). Starting from alkyl tartrates, we prepared spirophosphoranes with a P-H bond and sixco-ordinated compounds (7). With unprotected tartaric acid, many possibilities appear condensation as a diol, as a di(oc-hydro-xyacid), or even as a 8-hydroxyacid. 

Besides the dissociation of CO, the most common other ligand dissociation is that of a phosphine (PR3) or phosphite [P(OR)3]. There are two factors that influence the rate of dissociation of a phosphine—its donor ability and its cone angle. Both of these factors affect the M-P bond strength. Phosphines are better donors than phosphites because the P atom is more electron rich. For the same reason, alkyl phosphines are better donors than aryl phosphines (i.e., PMea > PPhs). Better donors create stronger Lewis acid-Lewisbase interactions with transition metals, and therefore dissociate slower. 

Similar carbonylations can be effected by treatment of transition metal <7-alkyls with ligands other than carbon monoxide, e.g. triphenyl phosphine, phosphites, primary amines or iodide ion ... 

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