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 phosphinetBu3P. 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)PtBu37. 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.