Subvalent group 13 molecules by carbene-induced hydrogen abstraction

Abstract

The N-Heterocyclic Carbene (NHC) alane and gallane adducts (NHC)·Cp*AlH₂ (NHC = Me₂Im^Me5, iPr₂Im^Me6, Dipp₂Im 7) and (NHC)·Cp*GaH₂ (NHC = Me₂Im^Me8, iPr₂Im^Me9, Dipp₂Im 10; R₂Im = 1,3-di-organyl-imidazolin-2-ylidene; Dipp = 2,6 diisopropylphenyl; Me₂Im^Me = 1,3,4,5-tetra-methyl-imidazolin-2-ylidene; Cp* = C₅Me₅) were prepared either via the reaction of (AlH₂Cp*)₃1 with the NHC or by the treatment of (NHC)·GaH₂I (NHC = Me₂Im^Me2, iPr₂Im^Me3, Dipp₂Im 4) with KCp*. The reaction of (AlH₂Cp*)₃1 with the backbone saturated NHC Dipp₂Im^H led to NHC ring expansion instead with the formation of (RER-Dipp₂Im^HH₂)AlCp* 12. Heating solutions of the gallium compounds 8–10 triggered reductive elimination of Cp*H and afforded Cp*Ga^I16. The reaction of the alane adduct (Me₂Im^Me)·Cp*AlH₂5 with cAAC^Me led to the insertion of cAAC^Me into the Al–H bond with the formation of the compound rac-(Me₂Im^Me)·AlHCp*(cAAC^MeH) rac-14. Heating a solution of rac-14 led to irreversible isomerisation with the formation of (Me₂Im^Me)·AlHCp*(cAAC^MeH) meso-14. The alane adducts (iPr₂Im^Me)·Cp*AlH₂6 and (Dipp₂Im)·Cp*AlH₂7 react with cAAC^Me with the release of the NHC and formation of the exceptionally stable oxidative addition product (cAAC^MeH)AlHCp* 15. Reactions of the gallane adducts 8–10 with cAAC^Me led to reductive elimination of cAAC^Me–H₂ and the formation of Cp*Ga^I16.