Heteroarylphosphorus compounds: Nickel(II) and cobalt(II) complexes of thienylphosphines

Abstract Complexes of a series of tertiary phosphines bearing 2-thienyl groups with nickel(II) and cobalt(II) halides and thiocyanates have been prepared and their magnetic and spectroscopic properties are presented. The nickel(II) halide and cobalt(II) halide and thiocyanate complexes have a distorted tetrahedral structure, whereas the nickel(II) thiocyanate complexes are square planar. Consideration of the spectroscopic data for the tetrahedral nickel(II) halide complexes of the thienylphosphines indicates that a 2-thienyl substituent is more electron-releasing towards phosphorus than is a phenyl group when the phosphorus is coordinated to the metal, suggesting that in this situation effects of pπ − dπ interactions between the heterocyclic ring system and phosphorus may be significant in influencing the donor properties of the phosphine. Calculation of the Racah parameters for the nickel(II) complexes indicates that the nephelauxetic effects of the thienylphosphines are different from those of triphenylphosphine and that there is a greater degree of covalency in the metal-ligand bond in the case of the thienylphosphines.