The first electron transfer chain catalyzed ligand substitution reaction that occurs by transforming an odd-electron system into an even-electron one
摘要:
The substitution of I- by Cl- in CpMoI2(PMe3)2 to afford CpMoCl2(PMe3)2 is catalyzed by 1-electron oxidation, which produces the paramagnetic 16-electron [CpMoI2(PMe3)2]+ complex. Halide substitution is more rapid on the 16-electron cationic complex than on the 17-electron neutral one to produce [CpMoCl2(PMe3)2]+, and an endoergic electron transfer step follows to close a catalytic cycle with constitutes the first reported electron transfer chain catalytic pathway in ligand substitution where exchange is made faster by going from an odd- to an even-electron system. The efficiency of the catalysis is low because of the endoergic electron transfer and because the 16-electron dichloride cation is decomposed by excess chloride. The [CpMoI2(PMe3)2]+ complex has been isolated in salts with the PF6-, I3-, and I- counterions. The interaction between CpMoI2(PMe3)2 and I2 in a 2:1 molar ratio shows that, after rapid formation of the [CpMoI2(PMe3)2]+I- salt, slow disproportionation occurs with formation of CpMoI2(PMe3)2 and [CpMoI2(PMe3)2]+I3-. The interaction between [CpMoCl2(PMe3)2]+ and Cl- has been investigated by NMR and cyclic voltammetry, which indicate the formation of the 18-electron CpMoCl3(PMe3)2, in equilibrium with the paramagnetic 16-electron CpMoC13(PMe3). The same equilibrium mixture has also been obtained from CpMoC12(PMe3)2 and PhI-Cl2 in a 2:1 molar ratio.