The Coordination Chemistry and Clustering of Subvalent Ga⁺ and In⁺ upon Addition of σ‐Donor Ligands

Abstract

This review addresses the coordination chemistry (mainly) enabled by using the univalent [M(fluoroarene) 2-3 ] + [Al(OR F ) 4 ] Àsalts (M=Ga, In; R F =C(CF 3 ) 3 ) as robust starting materials. In the course of this work, it became clear that the orbital energy of the ns 2 (n = 4, 5) lone pair in such [:M(L) n ] + cations reacts drastically depending on the quality of the ligand employed. Activation of the lone pair with strong σ-donor ligands might be used for bond activation and oxidative addition reactions. Yet, unexpectedly, using sterically undemanding and electron rich ligands with limited π-accepting properties, aggregation to highly charged and rather unusual univalent cluster cations [M n (L) m ]°+ (n = 2…5, m = 4…6, o = 3…5) was observed. An overview and rationalization of these findings is presented here.

Synthesis of a low-valent Al4+ cluster cation salt

“…However, VII cannot by prepared with a rational synthesis. Yet, cationic low-valent aluminium compounds are highly aspiring due to a potential transition-metal like ambiphilic reactivity 25 . Examples for a similar ambiphilicity were already reported for the more developed chemistry of cationic low-valent gallium and indium compounds [26][27][28][29] .…”

Synthesis and Reactivity of Cationic Gallium(I) [12]Crown-4 Complexes

“…Although gallium­(I) cations are present in “GaI”, gallium­(II) or gallium­(III) compounds are often isolated from reactions using this starting material. , Furthermore, “GaI” decomposes or comproportionates upon exposure to donor solvents such as ether and THF . When Ga 2 Cl 4 , which contains a gallium­(I) cation and a tetrachlorogallate­(III) anion ([Ga]­[GaCl 4 ]), is used as a starting material for the synthesis of gallium­(I) complexes, comproportionation reactions are common. − Although Krossing’s reagent, [Ga­(C 6 H 5 F) 2 ]­[Al­(OC­(CF 3 ) 3 ) 4 ], and derivatives with different arene ligands on the gallium­(I) center or counterions can be used as sources of gallium­(I) for synthesis and catalysis, the stability of [Ga­(C 6 H 5 F) 2 ]­[Al­(OC­(CF 3 ) 3 ) 4 ] in donor solvents has not been described . A study of the composition and structural chemistry of gallium­(I) triflate has recently been published; a mixture of mixed-valence complexes including Ga-arene, Ga-OTf complexes, and a naked Ga + has been identified .…”

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin, proof of oxidation with subvalent Ga+and silylium catalysis with perfluoroalkoxyaluminate anions

“…Classical Ga I -sources, e.g. "GaI", 1,2 Ga[GaX 4 ] (X = Cl, Br, I) 3 or GaCp ( * )4 do have some drawbacks in their application: they undergo facile dis-or comproportionation reactions upon addition of L4 ligands, 1,5,6 due to the presence of reactive and strongly coordinating counterions like [GaX 4 ] -7 or, for Green's "GaI", have a non-homogenous composition 1,8 that hampered systematic studies of Ga I chemistry for a long time. Subsequently, well-defined Ga I compounds like Ga I [ Dipp NacNac] ([ Dipp NacNac] -= [(Dipp)NC(Me)CHC(Me)N(Dipp)] -; Dipp = 2,6-diisopropylphenyl) 9 or Ga I [{(Dipp)N=CH} 2 ] 10 allowed to investigate the interesting carbene-like reactivity of Ga I (vide infra).…”

“…17,18 Both are suitable for coordination chemistry with classical L4 ligands. 6 In addition, Wehmschulte recently presented salts of the type [Ga(arene) x ]A with A = [CHB 11 Cl 11 ] or [B(C 6 F 5 ) 4 ] -. 19 Still, these carborate or borate salts are expensive and also difficult to synthesize, unlike the straightforward in large scale accessible [pf]salts.…”