Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] (1, L¹=dpp‐bian=1,2‐[(2,6‐iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3; R=Tos, 4). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] (5) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] (2; L²=dpp‐dad=[(2,6‐iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ (2 A), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} (6), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p‐MeC₆H₄)(N−C(O))₂−N(p‐MeC₆H₄)]₂ (7), cleavage of the C=O bond to yield the di‐O‐bridged digallium compound [Na(THF)₃]₂[L²Ga‐(μ‐O)₂‐GaL²] (8), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ (9). Complexes 3–9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X‐ray diffraction analysis. Their electronic structures have been examined by DFT calculations.