Spectroscopic studies magnesium halides

A proton resonance spectroscopic study of methanolic solutions of magnesium, zinc and aluminium perchlorates well reflected the effects of the cations on the solvent [Bu 69]. In the case of salts with different anions, however, the different hydrogen-bonding abilities of the anions could also be detected in the proton resonance spectrum. This is clearly seen, for example, from the data from PMR measurements on dimethylformamide solutions of halides [Mo 68]. 

A recent study showed that 152 behaves mechanistically different from other catalysts in addition reactions of more activated halides 140, such as trichloroacetate to styrene [222]. After initial reduction to Ru(II), chlorine abstraction from substrates 140 is in contrast to all other ruthenium complexes not the rate limiting step (cf. Fig. 36). ESR spectroscopic investigations support this fact. The subsequent addition to styrene becomes rate limiting, while the final ligand transfer step is fast and concentration-independent. For less activated substrates 140, however, chlorine abstraction becomes rate-determining again. Moreover, the Ru(III) complex itself can enter an, albeit considerably slower Ru(III)-Ru(IV) Kharasch addition cycle, when the reaction was performed in the absence of magnesium. This cycle operates, however, for only the most easily reducible halides, such as trichloroacetate. 

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