Preparation of η2-complexes of fullerenes by reduction. Crystal structure and optical properties of {Ni(dppp)·(η2-C70)}·(C6H4Cl2)0.5

Abstract

The new reduction method for preparation of η²-complexes of fullerenes with nickel–1,3-bis(diphenylphosphino)propane has been developed in which Ni(dppp)Cl₂ and C₆₀(C₇₀) mixtures are reduced with sodium tetraphenylborate. Single crystals of the first η²-complex of nickel with fullerene C₇₀: {Ni(dppp)·(η²-C₇₀)}·(C₆H₄Cl₂)_0.5 (1) (C₆H₄Cl₂ = o-dichlorobenzene) have been obtained as well as the previously described complex with fullerene C₆₀: {Ni(dppp)·(η²-C₆₀)}·(Solvent) (2). The crystal structure of 1 has been solved to show the coordination of nickel to the C–C bond of C₇₀ at the 6–6 ring junction of η²-type to form Ni–C(C₇₀) bonds of 1.929–1.941(2) Å length, the shortest M–C bonds among those known for η²-complexes of fullerenes C₆₀ and C₇₀. The length of the C–C bond to which Ni atom is coordinated (1.494(3) Å) is noticeably longer than the average length of these bonds in C₇₀ (1.381(2) Å). Optical spectra of 1 in the IR- and UV-visible ranges have been analyzed to show the splitting of some C₇₀ bands due to C₇₀ symmetry lowering. The complex has a red–brown color in solution and manifests three bands in the visible range at 379, 467 and 680 nm. The solution of 1 is air sensitive since air exposure restores the color and absorption bands of the starting C₇₀ at 383 and 474 nm.