Synthesis, Characterization and Real Molecule DFT Calculations for Neutral Organogallium(I) Aryl Dimers and Monomers: Weakness of Gallium-Gallium Bonds in Digallenes and Digallynes.

A series of stable aryl gallium(I) terphenyl derivs. was synthesized and characterized spectroscopically, structurally and by d. functional calcns. Dimeric structures with trans-bent planar CGaGaC core arrangements were obsd. for [(GaAr*-4-tBu)2] (7, Ar*-4-tBu = C6H2-2,6(C6H2-2,4,6-iPr3)2-4-tBu) and [(GaAr*-4-CF3)2] (8, Ar*-4-CF3 = C6H2-2,6(C6H2-2,4,6-iPr3)2-4-CF3), whereas monomeric structures featuring one coordinate gallium were obsd. for the more crowded complexes [:GaAr*-3,5-iPr2] (10, Ar*-3,5-iPr2 = C6H-2,6(C6H2-2,4-6-iPr3)2-3,5-iPr2) and [GaAr'-3,5-iPr2] (11, Ar'-3,5-iPr2 = C6H-2,6(C6H3-2,6-iPr2)2-3,5-iPr2). Complexes 7 and 8 dissoc. to monomers in hydrocarbon soln. and their electronic spectra closely resemble those of 10 and 11 as well as those of [Ar'GaGaAr'] (Ar' = C6H3-2,6(C6H3-2,6-iPr3)2) and [(GaAr*)n] (Ar* = C6H3-2,6(C6H2-2,4,6-iPr3)2). The calcns. showed that the binding energies of the compds. are weak, resemble closed-shell interactions and av. ≈5 kcal mol-1, as in [Ar*GaGaAr*] with a lowest value of ≈-2 kcal mol-1 for monomeric 10 and a highest value ≈9 kcal mol-1 for the least crowded species [Ar'GaGaAr']. The weak bonding in the complexes supports the view that the GaGa bonding in the previously published doubly reduced Na2[Ar*GaGaAr*] and Na2[Ar'GaGaAr'] is also weak and is consistent with approx. single bonding. [on SciFinder(R)]