Molecular versus Ionic Structures in Adducts of GaX₃ with Monodentate Carbon-Based Ligands

Abstract

A molecular donor-acceptor adduct has been isolated by the reaction of the N-heterocyclic carbene 1,3-dimethyl imidazol-2-ylidene (diMe-IMD) with GaCl(3). In contrast, the structurally related, yet much more nucleophilic, 1,3-dimethyl-2-methylene-2,3-dihydro-1H-imidazole (diMe-MDI) gave rise to ion pairs of type [L(2)GaX(2)][GaX(4)], where X = Cl, Br, or I. With IBioxMe(4), a N-heterocyclic carbene that is more nucleophilic than diMe-IMD, the outcome of the reaction was dependent on the nature of the halide. Ionic 1:1 adducts between monodentate ligands and GaX(3) salts have only one precedent in the literature. The peculiar behavior of carbon-based ligands was explained on the basis of their electronic properties and reaction kinetics.

New Procedures for Catalytic Carbophilic Activation by Gold and Gallium π-Acids

“…34 In the gallium series, with monodentate phosphines and N-heterocyclic carbenes (NHCs), only one ionic complex of type C has been characterized crystallographically: [(IBioxMe 4 ) 2 GaCl 2 ]GaCl 4 (Figure 2). 15 All the others are molecular B-type species in the solid state, for instance IPr·GaCl 3 , (IBioxMe 4 )·GaBr 3 or CAAC·GaCl 3 . 13, 35 For complexes of 1:1 ratio between the ligand and GaX 3 , the preference for the C-type ion pair or the B-type molecular adduct stems from a subtle balance between the steric hindrance and electronic effects brought about by the ligand.…”

“…13, 35 For complexes of 1:1 ratio between the ligand and GaX 3 , the preference for the C-type ion pair or the B-type molecular adduct stems from a subtle balance between the steric hindrance and electronic effects brought about by the ligand. 15 Increasing its Lewis basicity increases the pyramidalization of the gallium center 14,36 and consequently the leaving ability of the halide. 15 With bidentate phosphines, although molecular adducts are the most common (X 3 M P~P MX 3 ), ion pairs can be obtained sometimes (C, E, or F).…”

“…15 Increasing its Lewis basicity increases the pyramidalization of the gallium center 14,36 and consequently the leaving ability of the halide. 15 With bidentate phosphines, although molecular adducts are the most common (X 3 M P~P MX 3 ), ion pairs can be obtained sometimes (C, E, or F). 37…”

“…Addition of an organoligand to these species can give rise to bench-stable complexes. For example, the reaction of a carbon-based ligand 12 with a gallium(III) halide (GaX 3 ) species gives complexes of the type L•GaX 3 13,14 or [L 2 •GaX 2 ][GaX 4 ], 15 which are often easy-to-handle compounds. As their stability is due to their saturated nature (8-electron species), they cannot be used as π-acids unless a vacant site is generated on gallium.…”

Using the Type II Cycloisomerization Reaction of 1,6‐Enynes as a Mechanistic Probe to Identify the Real Catalytic Species of GaX3 and InX3

“…[13] It was also found that ligands can facilitate GaCl 3 dissociation. [14] To get further evidence of GaCl 2 + as the catalytic species, a stoichiometric cycloisomerization reaction of 1 catalyzed by GaCl 3 (120 mol %) was carried out in CH 3 CN solution at room temperature. In this case, nonconjugated product 2 was detected by gas chromatography with E/Z = 2:1 (Scheme 4).…”