Rhodium complexes three-coordinate

In 2002, Sakaki and coworkers carried out a theoretical study on the mechanism of hydrogenation of CO2 catalyzed by the three-coordinate, 14e d monohydride model complex RhH(PH3)2 [13]. It was found that CO2 insertion into the Rh-H bond is almost barrierless. This result suggests that the 14e rhodium(I) hydride is very reactive toward CO2. The COj insertion leads to formation ofthe rhodium (I) formate intermediate Rh(PHg)2(0C(0)H). To the rhodium(I) formate intermediate, oxidative addition of H2, which leads to formation of a dihydride complex, requires a barrier of 7.3 kcal mol". Then the reductive elimination of formic acid in the dihydride complex via a five-membered ring transition state (1) was calculated to have a very small barrier of 1.9 kcal mol . In the o-bond metathesis pathway, a barrier of only 6.1 kcal mol" was calculated. The o-bond metathesis... 

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