Hydride Amide and Hydride Phenolate Complexes of NHC Coordinated Aluminum

The reaction of NHC alane adducts NHC center dot AlH3 (NHC = N-Heterocyclic Carbene; NHC = iPr(2)Im, Dipp(2)Im; R(2)Im = 1,3-di-organyl-imidazolin-2-ylidene; iPr = isopropyl; Dipp = 2,6-diisopropylphenyl) with secondary amines HNR2 [R = iPr, Ph, Si(CH3)(3)] and the reaction of the trimethylamine alane adduct (NMe3)center dot AlH3 with secondary amines followed by the reaction with the NHC both lead to formation of the compounds NHC center dot AlH2(NR2) 1-6 [NHC = iPr(2)Im, Dipp(2)Im, R = iPr, Ph, Si(CH3)(3)]. These compounds are stable in solution up to temperatures of 90 degrees C. In contrast to the NHC alane adduct (iPr(2)Im)center dot AlH3 (I) and (Dipp(2)Im)center dot AlH3 (II), no ring expansion reaction to six-membered heterocyclic rings or ring opening reaction were observed for the reaction of (iPr(2)Im)center dot AlH2(NR2) with another equivalent of the NHCs iPr(2)Im or Dipp(2)Im. Thus, amide substituted NHC alane adducts show a much high stability compared to the parent compounds NHC center dot AlH3. Furthermore, the reaction of NHC center dot AlH3 (NHC = iPr(2)Im, Dipp(2)Im) with 2,4,6-trimethylphenol leads to the formation of the adducts NHC center dot AlH3-n(OMes)(n) 7-10 (n = 1, 2). The reaction with n >= 3 equivalent of 2,4,6-trimethylphenol afforded the imidazolium salt [Dipp(2)ImH](+)[Al(OMes)(4)](-) (11). The compounds 7-11 are also stable with respect to ring expansion after addition of another equivalent NHC.