Reactivity of frustrated Lewis pairs with BOC protected diazocarboxylates: FLP capture of diazene

Abstract

Reactions of (tBuO₂CN)₂ with FLPs are examined. B(C₆F₅)₃ interacts with the carbonyl oxygen atoms inducing loss of CH₂CMe₂; however, in the presence of basic donors, the protons are intercepted affording the salts [Hbase]₂ [((C₆F₅)₃BO₂CN)₂] (base = tBu₃P 1, NC₅H₂Ph₃2, HNC₅H₆Me₄3). In contrast, in the presence of (o-Tol)₃P, a proton transfers to the diazo-N atom affording (o-Tol)₃PN(CO₂tBu)NHB(C₆F₅)₃4. Further addition of B(C₆F₅)₃ to 4 prompts loss of olefin CH₂CMe₂ and CO₂ affording (o-Tol)₃PNHNHB(C₆F₅)₃5. The course of these reactions is examined by extensive DFT calculations. The nature of 5 is consistent with the FLP reduction of a diazene fragment.