Ligand synthesis arsenic ligands

Figure 4.25 Biarsenical ligands. Synthesis of Flash EDT2 and proposed structure of its complex with an a-helical tetracysteine-containing peptide or protein domain. The structure is drawn with the i and i +4 thiols bridged by one arsenic and the / + 1 and / + 5 thiols bridged by the other (Reproduced from Griffin et al., 1998, Fig. 1).

The synthesis of stable complexes with transition metal-phosphorus triple bonds is of fundamental importance and opens a novel chapter of a special field of coordination chemistry. The synthesis of analogous complexes with ligands of the heavier homologues like arsenic has partially been carried out [6], while for antimony and bismuth, the elusive M=Sb and M=Bi systems have now moved within reach. Moreover, the experimental and theoretical... 

Phosphorus, arsenic, and antimony donor ligands. A general synthesis has been reported for trialkyl phosphite complexes of noble metals, including [RuLeJ, [RuXLsl, and [RuHLs]+ [L = P(OMe)3 or P(OEt)3 X = Cl or Br]. The complexes were isolated as their tetraphenylborate salts from reaction of the phosphite with methanolic solutions of suitable labile olefin... 

The toxic forms of arsenic are mainly (Section III,A) compounds of the type R—AsX2, where X is a ligand that is easily displaced by thiols. Many such compounds are volatile, and this increases their hazard. As mentioned in Section VII,A,2, one such compound, Cl2As— CH2—AsC12, is a convenient intermediate in the synthesis of the diphosphate analogue H203As—CH2—As03H2. Obviously, its distillation and that of any similar compound should be performed in a fume... 

Probably one of the commonest reactions encountered in the template synthesis of macrocycles is the formation of imine C=N bonds from amines and carbonyl compounds. We have seen in the preceding chapters that co-ordination to a metal ion may be used to control the reactivity of the amine, the carbonyl or the imine. If we now consider that the metal ion may also play a conformational role in arranging the reactants in the correct orientation for cyclisation, it is clear that a limitless range of ligands can be prepared by metal-directed reactions of dicarbonyls with diamines. The Tt-acceptor imine functionality is also attractive to the co-ordination chemist as it gives rise to strong-field ligands which may have novel properties. All of the above renders imine formation a particularly useful tool in the arsenal of preparative co-ordination chemists. Some typical examples of the templated formation of imine macrocycles are presented in Fig. 6-12. 

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