(1,4)-Cycloaddition and C–X bond activation reactions of monovalent group 13 diyls

Abstract

Monovalent group 13 diyls of the type LM (L = HC[C(Me)NAr]₂; Ar = 2,6-ⁱPr₂C₆H₃) are group 13 analogues of NHCs. While LAl is known to undergo (1,4)-cycloaddition with a variety of dienes including arenes, LGa only reacted with acyclic dienes, i.e., butadiene and Danishefsky's diene, via (1,4)-cycloaddition to give LGa(C₆H₁₀) (1) and LGa(C₈H₁₆O₂Si) (2), whereas LIn completely failed to react with these substrates. However, LGa and LIn both reacted with the electron-poor hexachlorobutadiene with oxidative addition of the allyl C–Cl bond to give L(Cl)M(C₄Cl₅) (M = Ga 3; In 4). Similarly, L(X)MR (X = Cl, R = Bn, M = Ga 5, In 6; X = Br; R = Et, M = Ga 7, In 8) were obtained from oxidative addition with alkyl halides. Compounds 3–8 did not react with benzaldehyde, whereas the cation [LGaCH₂Ph]⁺ (10), obtained by reaction of L(Cl)GaBn with AgOTf and NaB(C₆F₅)₄, reacted rapidly, but no defined reaction product was identified.