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 = C6H3Pri2-2,6, 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)]RSnGa{N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, 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 = Pri2NC{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.