The synthesis and exchange chemistry of frustrated Lewis pair–nitrous oxide complexes

Abstract

Facile activation of nitrous oxide is achieved using a series of fluoroarylboranes, B(C₆F₅)₃, PhB(C₆F₅)₂, MesB(C₆F₅)₂, (C₆F₅)₂BOC₆F₅, B(C₆F₄-p-H)₃, B(C₆H₄-p-F)₃ and 1,4-(C₆F₅)₂BC₆F₄B(C₆F₅)₂ in the presence of the basic, bulky phosphine^tBu₃P. Room temperature reaction yields mono- and bis-zwitterionic species of the form ^tBu₃P(N₂O)B(C₆F₅)₂R (R = C₆F₅1, Ph 2, Mes 3, OC₆F₅4), ^tBu₃P(N₂O)BR₃ (R = C₆F₄-p-H 5, C₆H₄-p-F 6) and ^tBu₃P(N₂O)B(C₆F₅)₂C₆F₄(C₆F₅)₂B(ON₂)P^tBu₃7. N₂O activation is similarly achieved using Cy₃P and B(C₆F₄-p-H)₃ yielding the zwitterionic species Cy₃P(N₂O)B(C₆F₄-p-H)₃8. Reaction of 6 with [Ph₃C][B(C₆F₅)₄] results in facile transfer of the robust ^tBu₃P(N₂O) fragment to the stronger Lewis acid Ph₃C⁺ generating [^tBu₃P(N₂O)CPh₃][B(C₆F₅)₄] 10. Similarly exchange reactions with titanocene and zirconocene cations generate transition metal and phosphine stabilized nitrous oxide salts, of the form [^tBu₃P(N₂O)MCp₂Me][MeB(C₆F₅)₃], (M = Zr 11, Ti 12). The alkoxy zirconocene cation [Cp*₂Zr(OMe)]⁺ forms an FLP in the presence of ^tBu₃P which reacts with N₂O providing a direct synthetic route to the corresponding salt [^tBu₃P(N₂O)ZrCp*₂(OMe)][B(C₆F₅)₄] 13. Kinetic studies of the self-exchange reaction of ^tBu₃P(N₂O)B(C₆H₄-p-F)₃ with B(C₆H₄-p-F)₃ were carried out acquiring information regarding the mechanism of exchange.