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 = C6H3Pr2i-2,6, with the heavier group 14 alkene analogues, R2E = ER2, E = Ge or Sn, R = -CH(SiMe3)(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'E-2=EAr'(2), E = Ge, Sn or Pb, Ar' = C6H2Pr3i-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 = [(Pr2NC)-N-i{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.