Mononuclear Coordination Complexes of Fullerene C60 with Zerovalent Cobalt Having S = 1/2 Spin State: Co(η2-C60)(L)(C6H5CN)·(o-C6H4Cl2) (L = 1,2-bis(diphenylphosphino)ethane and 1,1′-bis(diphenylphosphino)ferrocene)

Abstract

Two mononuclear coordination complexes of fullerene C60 with cobalt, Co(η(2)-C60)(dppe)(C6H5CN)·C6H4Cl2 (1) and Co(η(2)-C60)(dppf)(C6H5CN)·C6H4Cl2 (2) (dppe is 1,2-bis(diphenylphosphino)ethane and dppf is 1,1'-bis(diphenylphosphino)ferrocene) have been obtained by sodium fluorenone reduction of the Co(dppe)Cl2 or Co(dppf)Br2 and C60 mixtures. The IR and visible-NIR spectra of 1 and 2 indicate the neutral state of fullerenes. Therefore, cobalt atoms formally have the zerovalent state. Cobalt coordinates to the 6-6 bond of C60 by η(2)-type coordination with Co-C bond lengths in the 2.008(3)-2.060(3) Å range. Diphosphine and benzonitrile ligands additionally coordinate to cobalt to form a distorted square-pyramidal environment for the cobalt atoms. Complexes 1 and 2 are rare examples of fullerene coordination complexes with paramagnetic metal centers. Both complexes manifest intense asymmetric EPR signals attributed to zerovalent cobalt atoms, which can be fitted by three components with g = 2.261-2.124 (1) and g = 2.258-2.092 (2). Effective magnetic moments of 1 and 2 indicate the low-spin (S = 1/2) state of Co(0). In accordance with EPR spectra, DFT calculations show that the spin density is localized mainly on the central cobalt atoms and only slightly delocalized into C60, benzonitrile, dppe, or dppf ligands.