N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene adducts of gallium hydrides, gallium chlorides and gallium hydrochlorides

摘要

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