Complexes Coordinated by 2,2′-Bipyridine Negative Ion. II. Sodium 2,2′-Bipyridinetetracarbonylchromium, -molybdenum, and -wolfram

Bipyridinetetracarbonylchromium, -molybdenum and -wolfram and their related complexes were reduced with sodium metal in tetrahydrofuran. Some products in the first stage of reduction were isolated. On the basis of the electronic absorption spectrum and the electron spin resonance, the complex formed in the reduction was concluded to be a complex coordinated by mononegative ion of bipyridine. Metal dσ orbital in the complex is still higher than bipyridine π* orbital, even if it is fairly lowered by a positive charge arising from the “metal to carbonyl” back-donation. Trapped electrons in the bipyridine π* orbital are, however, readily transferred into dσ orbital depending upon molecular environment. This gives rise to the formation of a pentacoordinate complex or complex dimer evolving carbon monoxide.