Nuclear magnetic resonance and electronic spectral studies on the formation of π–olefin-tetracyanocobaltate(I) complexes
Abstract
Cyanocobaltate prepared at CN : Co <5 : 1 in water in the presence of alkali and under an atmosphere of hydrogen reacts readily with mono-olefins having electron-withdrawing substituents to give a dark red solution. Hydrogen-1 and 13C n.m.r. spectra of the solutions in D2O clearly indicate that π-olefin complexes of cyanocobaltate are formed. The solutions also exhibit characteristic bands near 450 nm. The stoicheiometry of complex formation has been studied using PhCHC(CN)2 and monitored by the absorbance of the complex at 440 nm. These results indicate that a new type of π-olefin–cobalt(I) complex, [Co(CN)4(olefin)]3–, is formed, where olefin is (NC)2CC(CN)2, PhCHC(CN)2, cis- and trans-PhCHCHCN, E-PhCHC(CN)CO2Et, E-PhCHC(CN)CO2K, or cis- and trans-RO2CCHCHCO2R (R = Me, Et, or Na). The π complex of dialkyl maleate isomerises to that of dialkyl fumarate, probably by an electron-transfer mechanism.