Halometallates

A wide range of MX species exist, typical preparations appear below. 

Irlg does not exist Ir4+ is too strongly oxidizing to coexist with the reducing I-. 

Points to note in these syntheses include the use of BrF3 as an oxidizing agent, and the stability of IrXg-, also used as a source of IrX.  

Structural data [23] (Table 2.1) confirm the presence of the hexahaloanions in these states M2RhF7 (M = Sr, Pb) contain RhX - octahedra too, as do salts like (MeNH3)4RhX7 (X = Cl, Br) and (enH2)2RhX7. 

Many of the compounds in higher oxidation states are reactive, and for moisture-sensitive solids that cannot be crystallized, some of the bond lengths quoted in Table 2.1 are from EXAFS measurements [24], Raman spectroscopy is likewise well suited to studying such reactive compounds, and vibrational data for halometallates are given in Table 2.2 trends illustrated include the decrease in frequency as the oxidation state of the metal decreases, and similarly a decrease in vibrational frequency, for a given oxidation state, with increasing mass of the halogen. 

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Mixed halometallates [28] can be synthesized RhCl6Br l from the reaction of RhCl - with HBr, or RhBr - with HC1. Individual isomers have been identified in solution by 103 Rh NMR, which can even distinguish between stereoisomers (Figure 2.2) and shows isotopic splitting (Figure 2.3). 

So far no [Ni (Bu2dfc)3) complexes are found with any halometallate anion apart from [FeXj] (X = Cl, Br). 

Only a few recent examples of halogen bonding of halogenated TTFs with halometallate anions have been described and this most probably represents a broad development field in this area. Indeed, these halometallate salts offer a wide variety of complexes and specifically here a large variation of the ratio of anion charge vs number of halide atoms, as already discussed above in the comparison between Br and 13 salts. This point is illustrated by the superb structures of two salts of EDT-TTF-I2 with the polymeric one-dimensional PbV (Fig. 9) and two-dimensional (Pbs/eDi/eh) anions where shorter C -1- -Ianion contacts are observed with the linear Pbl3 chains... 

In the preparation of (2R,33, 7a3 )-2-phenyl-3-methyl-5-oxo-2,3,5,6,7,7a-hexahydropyrrolo-[2,T ]-oxazole 248, the reaction time is the most important parameter in the /ra r-halometallation. For instance, by stirring 246 with 1 or 2equiv of fer7-butyllithium in EtzO at — 78 °C for 30 min, 247 and the bicyclic lactam 248 were obtained as an equimolar mixture. The latter substance was isolated as a single product when the reaction time was increased to 120min for the reactions of 2-(2 -bromoethyl)oxazolidine 246 with fert-butyllithium (Scheme 36) <1996T10761>. 

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