Reactivity of bis(organoamino)phosphanes with magnesium(ii) compounds

Abstract

The reactivity of three phosphanes (PhP(NHR)₂ [R = t-Bu (1), Ph (2)] and PhP(NEt₂)(NHDip) (3) (where Dip = 2,6-i-Pr₂C₆H₃)) with n-Bu₂Mg and MeMgBr is presented. In the case of 1, the reaction with n-Bu₂Mg gave [PhP(NHt-Bu)(Nt-Bu)]Mg(n-Bu) (4) or [PhP(NHt-Bu)(Nt-Bu)]₂Mg (5) depending on the stoichiometry. The treatment of 1 with MeMgBr led to the phosphinate [Ph(H)P(Nt-Bu)₂]₂Mg (7) as a result of both the NH→PH tautomeric transformation and elimination of MgBr₂ from the non-isolable intermediate [PhP(NHt-Bu)(Nt-Bu)]MgBr(THF) (6). Phosphane 2 reacted with n-Bu₂Mg in a 1 : 1 molar ratio resulting in the formation of {[PhP(NPh)₂]₂Mg(THF)₂}₂ (8), but the analogous reaction in a 2 : 1 molar ratio yielded phosphinate [Ph(H)P(NPh)₂]₂Mg(THF) (9). The heteroleptic compound [Ph(H)P(NPh)₂]MgBr(THF)₂ (10) was obtained by the reaction of 2 with MeMgBr. Finally, the reaction of 3 with n-Bu₂Mg and MeMgBr produced compounds [PhP(NEt₂)(NDip)]₂Mg (11) and {[PhP(NEt₂)(NDip)₂]Mg(μ-Br)(THF)}₂ (12), respectively. All products were characterized using ¹H, ¹³C{¹H} and ³¹P NMR spectroscopy and, except for compounds 4 and 6, their molecular structures were determined using single-crystal X-ray diffraction analysis. In addition, a theoretical study on plausible isomers of 10 was performed to provide additional evidence for the presence of a syn- and anti-isomer in dynamic equilibrium in a solution of 10.