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

Facile activation of nitrous oxide is achieved using a series of fluoroarylboranes, B(C6F5)(3), PhB(C6F5)(2), MesB(C6F5)(2), (C6F5)(2)BOC6F5, B(C6F4-p-H)(3), B(C6H4-p-F)(3) and 1,4-(C6F5)(2)BC6F4B(C6F5)(2) in the presence of the basic, bulky phosphine (Bu3P)-Bu-t. Room temperature reaction yields mono-and bis-zwitterionic species of the form (Bu3P)-Bu-t(N2O)B(C6F5)(2)R (R = C6F5 1, Ph 2, Mes 3, OC6F5 4), (Bu3P)-Bu-t(N2O)BR3 (R = C6F4-p-H 5, C6H4-p-F 6) and (Bu3P)-Bu-t(N2O)B(C6F5)(2)C6F4(C6F5)(2)B(ON2)(PBu3)-Bu-t 7. N2O activation is similarly achieved using Cy3P and B(C6F4-p-H)(3) yielding the zwitterionic species Cy3P(N2O)B(C6F4-p-H)(3) 8. Reaction of 6 with [Ph3C][B(C6F5)(4)] results in facile transfer of the robust (Bu3P)-Bu-t(N2O) fragment to the stronger Lewis acid Ph3C+ generating [(Bu3P)-Bu-t(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 [(Bu3P)-Bu-t(N2O)MCp2Me][MeB(C6F5)(3)], (M = Zr 11, Ti 12). The alkoxy zirconocene cation [Cp*Zr-2(OMe)](+) forms an FLP in the presence of (Bu3P)-Bu-t which reacts with N2O providing a direct synthetic route to the corresponding salt [(Bu3P)-Bu-t(N2O)ZrCp*(2)(OMe)][B(C6F5)(4)] 13. Kinetic studies of the self-exchange reaction of (Bu3P)-Bu-t(N2O)B(C6H4-p-F)(3) with B(C6H4-p-F)(3) were carried out acquiring information regarding the mechanism of exchange.