Tetrahedral cobalt(II) complexes stabilized by the aminodiphosphine PNP ligand [PNP = CH3CH2CH2N(CH2CH2PPh2)2]

The reaction of CoCl2·6H2O and PNP [PNP = 1,1-bis(diphenylphosphinoethyl)-n-propylamine (CH3CH2CH2)N(CH2CH2PPh2)2] in ethanol affords the blue Co(II) complex [CoCl3{(eta)^1-PPPh2CH2CH2N(CH2CH2CH3)(H)(CH2CH2P(O)Ph2)}](1), which has been characterized by spectroscopic methods and X-ray diffraction analysis. The structure of 1 consists of a tetrahedral cobalt atom coordinated by three chlorides and by an (eta)^1-P-PNP ligand bearing a dangling P=O end and quaternised at the nitrogen atom. EPR measurements and a detailed analysis of the magnetic behaviour of 1 are consistent with a tetrahedral Co(II) ion and accordingly support the protonation of the PNP nitrogen atom. A mechanistic picture accounting for the formation of 1 has been proposed from the isolation and characterization of three reaction intermediates along the pathway leading to 1 which involve either (eta)^2-P,P- and (eta)^2-P,N-PNP cobalt complexes.