Formation constants of some phosphine and phosphite adducts of (η5-cyclopentadienyl) (substituted 1,2-ethylenedichalcogenolato) cobalt(III) complexes and their 1H, 13C and 31P NMR spectra

Abstract The formation constants of the phosphine and phosphite adducts of several (η 5 -cyclopentadienyl) (substituted 1,2-ethylenedithiolato) cobalt(III) complexes in acetonitrile were determined spectrophotometrically. The complexes with more electron-withdrawing substituents on the ditholate ligand form more stable adducts. The NMR chemical shifts ( 1 H, 13 C and 31 P) of the complexes, phosphines, phosphites and adducts were measured in CDCl 3 . The shifts were changed on adduct formation. These changes indicate that the phosphines act as σ-donors and the phosphites as π-acceptors and that the cobaltadithiolene ring, which is aromatic in the unbound complex, becomes olefinic in the adduct.