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

Abstract Digallane [L 1 Ga−GaL 1 ] ( 1 , L 1 =dpp‐bian=1,2‐[(2,6‐ i Pr 2 C 6 H 3 )NC] 2 C 12 H 6 ) 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 [L 1 (O=C−NR)Ga−Ga(RN−C=O)L 1 ] (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 [L 1 Ga−Ga(AllN− C=O) 2 L 1 ] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L 2 Ga−GaL 2 ] ( 2 ; L 2 =dpp‐dad=[(2,6‐ i Pr 2 C 6 H 3 )NC(CH 3 )] 2 ) is converted into the gallium(I) carbene analogue [L 2 Ga:] − ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na 2 (THF) 5 ]{L 2 Ga[EtN−C(O)] 2 GaL 2 } ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF) 2 ] 2 [L 2 Ga( p ‐MeC 6 H 4 )(N−C(O)) 2 −N( p ‐MeC 6 H 4 )] 2 ( 7 ), cleavage of the C=O bond to yield the di‐ O ‐bridged digallium compound [Na(THF) 3 ] 2 [L 2 Ga‐(μ‐O) 2 ‐GaL 2 ] ( 8 ), and generation of the further addition product [Na 2 (THF) 5 ][L 2 Ga(CyNCO 2 )] 2 ( 9 ). Complexes 3 – 9 have been characterized by NMR ( 1 H, 13 C), IR spectroscopy, elemental analysis, and X‐ray diffraction analysis. Their electronic structures have been examined by DFT calculations.