N-Heterocyclic Carbene and Cyclic (Alkyl)(Amino)Carbene Adducts of Gallium Hydrides, Gallium Chlorides and Gallium Hydrochlorides

The synthesis and characterization of N-Heterocyclic carbene (NHC) and cyclic (alkyl)(amino)carbene (cAAC) gallane and chlorogallane adducts of the type (NHC)∙GaH3 (NHC = Me2ImMe 1, iPr2Im 2 and Dipp2ImH 3; Me2ImMe = 1,3,4,5-tetra-methyl-imidazolin-2-ylidene; R2Im = 1,3‐di-organyl-imidazolin-2-ylidene; Dipp = 2,6-diisopropylphenyl; Dipp2ImH= 1,3‐bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene), (NHC)∙GaH2Cl (NHC = iPr2ImMe 9, Dipp2Im 10 and Dipp2ImH 11; iPr2ImMe = 1,3 diisopropyl-4,5-dimethyl-imidazolin-2-ylidene), (NHC)∙GaHCl2 (NHC = iPr2ImMe 12, Dipp2Im 13 and Dipp2ImH 14) and (cAACMe)∙GaHCl2 15 is reported. Compounds 1-3 and 9-11 are unstable in solution as heating to the boiling of toluene (110°C) leads to decomposition into elemental gallium and the corresponding dihydroaminal NHC-H2. Reaction of the mono-NHC adducts with a second equivalent of NHC also afforded decomposition and formation of NHC-H2, whereas the reaction of the NHC-stabilized gallanes with one equivalent cAACMe leads to insertion of the cAACMe carbene carbon atom into the Ga-H bond. The synthesis and characterization of (NHC)∙GaH2(cAACMeH) (NHC = Me2ImMe 5, iPr2ImMe 6 and Dipp2Im 7), the products of an oxidative addition of (NHC)∙GaH3 to cAACMe, are presented. The adduct (Dipp2ImH)∙GaH3 3 reacts with two equivalents of cAACMe under release of Dipp2ImH and insertion of two cAACMe molecules into the Ga-H bonds to give the bisalkylgallane (cAACMeH)2GaH 8. If one or two hydrogen atoms of the NHC gallane adducts are replaced with an electronic withdrawing chloride substituent selective insertion of the cAACMe into the Ga-H bond occurs only for the adducts of sterically less demanding NHCs such as iPr2ImMe. The reaction of cAACMe with (iPr2ImMe)∙GaH2Cl 9 and (iPr2ImMe)∙GaHCl2 12 afforded (iPr2ImMe)∙GaHCl(cAACMeH) 16 and (iPr2ImMe)∙GaCl2(cAACMeH) 17. The reaction of cAACMe with (NHC)∙GaHCl2 and (NHC)∙GaH2Cl (NHC = Dipp2Im, Dipp2ImH), adducts of the sterically more demanding NHCs, lead with extrusion of the NHC to (cAACMe)∙GaHCl2 15 and (cAACMeH)2GaCl 18.