Oxidative addition of tetrachloro-1,2-benzoquinone to λ³-cyclotriphosphazanes. An unusual ring contraction-rearrangement

Abstract

The λ³-cyclotriphosphazanes, [EtNP(OR)]₃ [R = 2,6-Me₂C₆H₃ (1), 4-BrC₆H₄ (2), or CH₂CF₃(3)], on treatment with tetrachloro-1,2-benzoquinone (TCB) give the λ⁵-cyclodiphosphazanes, [EtNP(O₂C₆Cl₄)(OR)][EtNP(O₂C₆Cl ₄){N(Et)P(OR)₂}] (5-7) by an unusual ring contraction-rearrangement. The reaction of the mixed substituent λ³-cyclotriphosphazane, [(EtN)₃P₃(OR)₂(OR')] [R = 2,6-Me₂C₆H₃, R' = 4-BrC₆H₄] (4), with TCB gives the λ⁵-cyclodiphosphazane, [EtNP(O₂C₆Cl₄)(OR')][EtNP(O₂C₆Cl ₄){N(Et)P(OR)₂}] (8), in which 4-bromophenoxide resides on one of the ring phosphorus atoms. The λ³-bicyclic tetraphosphapentazane, (EtN)₅P₄(OPh)₂, on treatment with TCB undergoes a double ring contraction-rearrangement to give the λ⁵-cyclodiphosphazane, (EtN)[(EtN)₂P₂(O₂C₆Cl₄) ₂(OPh)]₂ (9). Variable-temperature and high-field ³¹P NMR studies indicate the presence of more than one isomer in solution for the rearranged products 5-9. The solid state structure of 8 reveals a trans arrangement of the substituents with respect to the P₂N₂ ring in contrast to the gauche arrangement observed for 5.