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

Abstract

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 = C(6)H(2)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)-4-tBu) and [(GaAr*-4-CF(3))(2)] (8, Ar*-4-CF(3) = C(6)H(2)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)-4-CF(3)), whereas monomeric structures featuring one coordinate gallium were observed for the more crowded complexes [:GaAr*-3,5-iPr(2)] (10, Ar*-3,5-iPr(2) = C(6)H-2,6(C(6)H(2)-2,4-6-iPr(3))(2)-3,5-iPr(2)) and [GaAr'-3,5-iPr(2)] (11, Ar'-3,5-iPr(2) = C(6)H-2,6(C(6)H(3)-2,6-iPr(2))(2)-3,5-iPr(2)). 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' = C(6)H(3)-2,6(C(6)H(3)-2,6-iPr(3))(2)) and [(GaAr*)(n)] (Ar* = C(6)H(3)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)). The calculations showed that the binding energies of the compounds are weak, resemble closed-shell interactions and average approximately 5 kcal mol(-1), as in [Ar*GaGaAr*] with a lowest value of approximately -2 kcal mol(-1) for monomeric 10 and a highest value approximately 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 Na(2)[Ar*GaGaAr*] and Na(2)[Ar'GaGaAr'] is also weak and is consistent with approximate single bonding.

Dialumenes – arylvs.silyl stabilisation for small molecule activation and catalysis

“…On descending group 13, heavier digallenes and dithallenes have been isolated which show notable trans-bent character and have been known to dissociate to their corresponding monomers in hydrocarbon solutions. [21][22][23][24][25] However, digallanes have been shown to react as the double bonded species, rather than the monomer with regards to cycloadditions of unsaturated C-C bonds and even dihydrogen activation. [26][27][28] Motivated by our group's previous efforts in dialumene chemistry, we targeted the isolation of a neutral aryl-stabilised dialumene to compare the intrinsic nature of the aluminiumaluminium double bond through the inuence of ligand stabilisation.…”

Heterodiatomic Multiple Bonding in Group 13: A Complex with a Boron–Aluminum π Bond Reduces CO2

“…Thep roperties of these molecules have been discussed alternatively in the context of the Carter-Goddard-Malrieu-Trinquier model (CGMT), [34][35][36][37][38][39] of MO theory and of singlet biradicals.A ccording to the CGMT model, double bonding is increasingly described as the dimerization of singlet fragments upon moving down the group.This explains the distorted geometries,relative lability,and the observation of Wanzlick-type equilibria in these heavy compounds. [40][41][42][43] Alternatively or complementarily,amixing of p and s* orbitals [44,45] or abiradicaloid ground state can be invoked. [46] Unfortunately,t he dearth of experimental data on Group 13 multiple bonds limits the advancement of the field.…”

Heterodiatomare Mehrfachbindung zwischen Elementen der Gruppe 13: Ein Komplex mit B‐Al‐π‐Bindung reduziert CO2

“…Trotz des zähen Starts erbrachten die letzten Jahrzehnte einige neutrale Diborene, [19][20][21][22][23] Diborine, [24][25][26] Diboracumulene, [27] Dialene [28] und Digallene. [40][41][42][43] Alternativ bzw.komplementärkann eine Durchmischung der p-u nd s*-Orbitale [44,45] oder ein biradikalischer Grundzustand in Betracht gezogen werden. Die Eigenschaften dieser Verbindungen wurden alternativ mit dem Carter-Goddard-Malrieu-Trinquier-Modell (CGMT), [34][35][36][37][38][39] der MO-Theorie und mit Singulett-Biradikalen erklärt.…”

“…Weiterhin erklärt dieses Modell die verzerrte Geometrie,die relative Labilitäts owie das beobachtete,W anzlick-artige Gleichgewicht dieser schweren Mehrfachbindungen. [40][41][42][43] Alternativ bzw.komplementärkann eine Durchmischung der p-u nd s*-Orbitale [44,45] oder ein biradikalischer Grundzustand in Betracht gezogen werden. [46] Bedauerlicherweise beschränkt das Defizit an experimentellen Daten von Gruppe-13-Mehrfachbindungen den Fortschritt in diesem Bereich.…”