Syntheses and characterisation of rhenium-(III) and -(V) complexes containing aminophosphine ligands. Crystal structures of [ReVOCl2(OMe)L] and [ReIIICl3L(PPh3)], L = o-(diphenylphosphino)-N ,N′-dimethylaniline

Abstract

Substitution reactions of labile rhenium(V) precursors with o-(diphenylphosphino)-N,N′ -dimethylaniline, L, gave a series of monooxorhenium(V) complexes of general formula [ReOX ₂ Y(L)] (X = Y = Cl 1; X = Cl, Y = OMe 2) and [ReOX ₂ (OEt)L] (X = Cl 3, Br 4 or I 5). These complexes, which contain only one aminophosphine chelate, have a distorted-octahedral geometry, as evidenced by a crystal structure determination of 2. Reactions conducted in basic media, or treatment of 2 in the presence of the weakly co-ordinating trifluoromethanesulfonic acid, gave the bis(chelate) cationic complexes [ReO ₂ L ₂ ] ⁺ 6 and [ReCl ₂ L ₂ ] ⁺ 7, respectively. Similar ligand-exchange reactions between the lower-oxidation-state precursor [Re ^III Cl ₃ (MeCN)(PPh ₃ ) ₂ ] and L or L′ [o-(diphenylphosphino)aniline] still produced mono-substituted aminophosphine complexes, i.e. [Re ^III Cl ₃ L(PPh ₃ )] 8 or [Re ^III Cl ₃ L′(PPh ₃ )] 9 in which there is a meridional arrangement of chloride ligands along with a cis-phosphorus co-ordination. The crystal structure of 8 was determined. On the contrary, treatment of [Re ^III X ₃ (MeCN)(PPh ₃ ) ₂ ] (X = Cl or Br) with L′ in the presence of co-ordinating hydrohalogenic acid gave bis-substituted cationic complexes [ReX ₂ L′ ₂ ] ⁺ (X = Cl 10 or Br 11). In spite of the paramagnetism of the low-spin d ⁴ ion, all of the rhenium(III) complexes can be conveniently characterised in solution by proton NMR spectroscopy.