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)

Two mononuclear coordination complexes of fullerene C-60 with cobalt, Co(eta(2)-C-60)(dppe)(C6H5CN)center dot C6H4Cl2 (1) and Co(eta(2)-C-60)(dppf)(C6H5CN)center dot 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)Cl-2 or Co(dppf)Br-2 and C-60 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 C-60 by eta(2)-type coordination with Co-C bond lengths in the 2.008(3)-2.060(3) angstrom 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 C-60, benzonitrile, dppe, or dppf ligands.