Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: Synthetic, structural and theoretical studies

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H 3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe 3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)] 2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane(4), [Ga{[N(Ar)C(H)] 2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar′2E=EAr′2, E = Ge, Sn or Pb, Ar′ = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)] [Ar′2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar′Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pr i2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies. © 2006 American Chemical Society.