Halogen-bridged cations

Compounds having divalent sulfur and selenium atoms bound to more electronegative elements react with alkenes to give addition products. The mechanism is similar to that in halogenation and involves of bridged cationic intermediates. 

There are a number of examples known from weak-halogen bridges between T-shaped Y-Te-X complexes, like tuTe(Ph)Cl [Figure 30(a)] related weak cation-anion interaction occurs in the 2 1 complex [tu2Te(Ph)]+ Cl- [Figure 30(b)], The weak contact is generally the one trans to the Te-C bond ( trans effect of the strong Te-C bond).84,85... 

A systematic study of the alkylation of benzene with optically active 1,2-, 1,3-, 1,4-, and 1,5-dihaloalkanes showed that the stereochemical outcome depends on the halogens and the chain length.142 Retention of configuration in alkylation with (S)-1,2-dichloropropane was explained by invoking double inversion and the involvement of a bridged cation such as 27. (S)-l-Bromo-2-chloropropane, in contrast,... 

The far IR spectra of the [Znd4]2- anion in salts with the 1,10-phenanthrolinium and 2,2-bipyridinium cations have been reported.1039 The anion in the former salt appears to be tetrahedral, while that in the latter is believed to be halogen-bridged. 

As already mentioned, the binuclear cations react with several donor molecules with cleavage of the halogen bridge however, only ligands that do not react with the cyclopentadienyliron dicarbonyl halides can be used in this reaction, as the latter are... 

It is important to note that in all known structures, the anions make very close contacts, via halogen bridges, with the cations. Two representative structures illustrating this point are shown in Fig. 13-3. 

With large cations halogen-bridged dimers such as [Rh2Cl9]3, Rh2Cl (PEt3)3, and [Rh2Cl7(PR3)2] can be obtained.30... 

The concept of a halonium ion solves both of the problems associated with an open carbonium ion a halogen bridge prevents rotation about the carbon-carbon bond, and at the same time restricts bromide ion attack exclusively to the opposite face of the cation. This opposite-side approach, we shall find (Sec. 14.10), is typical of attack by bases (nucleophiles) on tetrahedral carbon. 

In 2006, Genet and Mashima developed a new and convenient one pot reaction to prepare mononuclear halide carboxylate iridium(III) complexes and cationic triply halogen bridged dinuclear iridium(III) complexes of BINAP, p TolBINAP, and SynPhos. These iridium(III) complexes were tested as catalyst precursors for asymmetric hydrogenation of 2 phenylquinoline (Scheme 10.8) [10]. Cationic iododi nuclear p TolBINAP (S) L6e and SynPhos (S) L3c complexes had better enantios... 

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