Rhodium complexes tertiary stibine

Bridging coordination of a tertiary stibine ligand (type 2) occurs in binuclear complexes of rhodium (Equation 1).13,14... 

There is an extensive chemistry of tertiary phosphine rhodium(III) complexes. However, there are comparatively few complexes of monodentate tertiary arsines, although the complexes of ditertiary arsines are more numerous. There are virtually no tertiary stibine complexes. The two main preparative routes to the complexes described in this section are (i) direct reaction pf the ligands with rhodium trichloride, which usually yields trichloro complexes and (ii) oxidative addition to rhodium(I) tertiary phosphine complexes, which gives rise to more diverse products of the type [RhXYZ(PRj) ], Metathetical reactions on the complexes prepared by either method (i) or (ii) have been used to prepare most of the remaining compounds. 

One interesting reaction undergone by the tri(styryl)arsine complexes is the bromination of the C=C bond by bromine in CC14 (equation 217).1013 Similar behavior970 is exhibited by the few tertiary stibine complexes (Table 75) that have been isolated. Few physical properties of these complexes have been investigated, but the 121 Sb Mossbauer parameters for both rhodium(III) complexes and the free ligands have been determined.1016... 

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

To some extent this situation has been rectified by a number of reviews of more limited range. Among these are the review by Robinson on the rhodium(II) carboxylates,19 and the reviews on the chemistry of [RhCl(PPh3)3]20 and [RhH(CO)(PPhj)3].21 The tertiary phosphine, arsine and stibine complexes of the element have also been covered in two reviews of these ligands complexes with the transition elements.22... 

Table 14b Magnetic Properties and Far-IR Spectra of Rhodium(II) Complexes of Tertiary Phosphines and Stibines...

Apart from the triethylarsine972 and the tribenzylarsine974 complexes the remaining tertiary arsine complex is formed by the ditertiary arsine l,2-(Ph2As)2C2H4 clearly this cannot adopt structure (80). However, the ditertiary stibine complexes976 may well adopt structure (80), since their stoichiometry implies that only half the antimony atoms are coordinated to rhodium. 

However, over the last 60 years a new type of chemistry has emerged. Although the first examples, tertiary arsine complexes, were initially prepared as an extension of classical rhodium(III) chemistry, the newer complexes containing tt-bonding ligands have been a consequence of the intense interest in the catalytic properties of rhodium(I) complexes. Examples of these ligands also include tertiary phosphines and stibines, although it is debatable to what extent they act as r-acids when coordinated to rhodium(III). 

Tuning Rhodium (I) Metal Centre A ccessibility in lodomethane Oxidative Addition to Vaska-type Complexes by Interchanging Tertiary Phosphine for Arsine and Stibine... 

By contrast tertiary arsine and stibine ligands do not displace alkadiene ligands and are only able to displace weakly bound alkene - or allyl " ligands from other rhodium(I) complexes. 

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