Four- and five-co-ordinate complexes of heterocyclic tertiary phosphines with nickel(II), palladium(II), and platinum(II) dihalides

Abstract

The effects of variation in the steric and electronic properties of a number of heterocyclic unidentate tertiary phosphine ligands on their ability to form five-co-ordinate tris(phosphine) complexes with nickel(II), palladium(II), and platinum(II) dihalides, have been studied.

In contrast to 5-methyl- and 5-ethyl-5H-dibenzophosphole (I; R = Me, Et) which give rise to a series of five-co-ordinate complexes with the above halides, both 5-isopropyl- and 5-t-butyl-5H-dibenzophosphole (I; R = Prⁱ, Bu^t) form only four-co-ordinate complexes of type (phos)₂MX₂. The nickel(II) dihalide complexes of this type have a tetrahedral structure, indicated by their magnetic and spectroscopic properties. ¹H N.m.r. studies show that in solution in deuteriochloroform, the four-co-ordinate Pd^IIBr₂ complexes of both the phosphines (I; R = Prⁱ) and (I; R = Bu^t) have the trans-configuration and the Pt^IICl₂ complex of (I; R = Bu^t) also has this configuration, whereas the Pt^IICl₂ complex of (I; R = Prⁱ) has the cis-configuration.

2,8-Dimethoxy-5-phenyl-5H-dibenzophosphole (II) resembles 5-phenyl-5H-dibenzophosphole (I; R = Ph) in forming four-co-ordinate, tetrahedral, nickel(II) dihalide complexes.

10-Methyl-10-phenoxaphosphine (IV; R = Me) forms five-co-ordinate tris(phosphine)MX₂ complexes with Ni^IICl₂, Pd^IIBr₂, and Pt^IICl₂. 10-Ethyl-10-phenoxaphosphine (IV; R = Et) forms five-co-ordinate complexes apparently only with Ni^IIBr₂ and Ni^IIl₂, four-co-ordinate species being formed with Ni^IICl₂ and Ni^II(NCS)₂ and also with Pd^IIBr₂ and Pt^IICl₂. 10-Phenyl-10-phenoxaphosphine (IV; R = Ph) forms only four-co-ordinate complexes with nickel salts.

The seven-membered cyclic triarylphosphine, 10,11-dihydro-5-phenyl-5H-dibenzo[b,f]phosphepin (V) is unusual in forming diamagnetic, square-planar, nickel(II) dihalide complexes.