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



Move closer: The gallium[BOND]gallium bond strength in terphenyl gallium(I) dimers [ArGaGaAr] (see figure) is similar to those in other molecules with closed shell interactions, implying that the Ga[BOND]Ga bond in doubly reduced Na2[ArGaGaAr] is much closer to a single than a triple one.

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A series of stable aryl gallium(I) terphenyl derivatives was synthesized and characterized spectroscopically, structurally and by density functional calculations. Dimeric structures with trans-bent planar CGaGaC core arrangements were observed 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 observed 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 dissociate to monomers in hydrocarbon solution 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 calculations showed that the binding energies of the compounds are weak, resemble closed-shell interactions and average ≈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 approximate single bonding.

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