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

Abstract

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{η¹-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 η¹-P-PNP ligand bearing a dangling PO 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 η²-P,P- and η²-P,N-PNP cobalt complexes.