Tertiary arsines complexes

There are no tertiary arsine complexes of rhodium(II). Early reports of such complexes are erroneous.5,6 The complexes have been shown to be hydridorhodium(III) species. 

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. 

The tertiary arsine complexes were first prepared by Dwyer and Nyholm,5 but, before the advent of NMR spectrometry, were erroneously considered to be rhodium(II) complexes.989 Further investigations have shown that in preparations starting from rhodium trihalides using a higher tertiary arsine rhodium ratio and lower reaction temperatures favor the formation of the p isomer (equations 205 and 206).986... 

The tertiary arsine complexes (Table 74) are much less numerous than those containing tertiary phosphines. They are usually prepared by the interaction of tertiary arsines with rhodium trihalides. The poorer reducing properties of tertiary arsines make it much less likely that rhodium(I) complexes will be formed in this reaction. 

Many of the methods that have been used to prepare the [Rh(NO)X2(PR3)2] complexes can be adapted to yield similar tertiary arsine complexes. For example, jV-methyl-A -nitrosotoluetie-p-sulfonamide still functions as a source of the nitrosyl ligand in the presence of tertiary arsines (equations 313 and 314). 

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). 

MeOC6H4)3As 3] and [Ga2l4(AsEt3)2], respectively. The last is a unique example of a gallium-tertiary arsine complex containing a Ga-Ga bond, and these complexes serve to illustrate the subtle effect of the organic substituent on the chemistry of the arsenic atom. 

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