σ‐ or π‐Coordination? Complexes of Univalent Gallium Salts with Aromatic Nitrogen Bases

Abstract

To answer the question as to whether gallium in its oxidation state +1 favors a σ‐ or a π‐coordination of aromatic nitrogen bases, we reacted [Ga(C6H5F)2]+[Al(ORF)4]– {RF = C(CF3)} with pyrazine and 2,6‐di‐tert‐butyl‐4‐methylpyridine (DTBMP). In doing so, we obtained the first tricoordinate, nonchelated, homoleptic N‐donor complex of gallium(I): [Ga(pyrazine)3]+[Al(ORF)4]–, in which each gallium(I) cation is coordinated in a trigonal‐pyramidal fashion by three η1‐donating pyrazine ligands. Hence, the gallium(I) cations favor σ‐ over π‐coordination. Depending on the reaction conditions, and due to the bifunctionality of pyrazine, 1D coordination polymers of {[Ga(μ‐pyrazine)2(η1‐pyrazine)]+[Al(ORF)4]–}∞ were also obtained. With the sterically demanding DTBMP, which is conventionally used as a proton scavenger, the mixed complex [Ga(C6H5F)2(DTBMP)]+[Al(ORF)4]– was isolated, thus proving incorrect the perception of DTBMP being “non‐nucleophilic”. The structural findings were confirmed by multinuclear NMR investigations and density functional performed at the RI‐BP86/SV(P) level.

Why Do Five Ga+ Cations Form a Ligand‐Stabilized [Ga5]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

“…Five dmap ligands are located above the plane of the ring and five below; the average Ga-N separation amounts to 2.033(4) pm (range:2.012(5) to 2.067-(4) pm) and is significantly shorter than other reported Ga I À N distances of this kind, for example,i nt he univalent pyrazine complex Ga(pyrazine) 3 4 ] À (average:2 33.0 pm). [10] This indicates aheavy involvement of DMAP in the bonding, as indicated by the resonance structures in Figure 1b,c. The neutral digallane(4) (disil) 2 Ga À Ga(disil) 2 (d GaÀGa = 254 pm; disil = À C(H)(SiMe 3 ) 2 ) [19] and the dumbbells of elemental agallium (246 pm) hold similar GaÀGa distances to 1 5+ .…”

“…[4] However,r elated chemistry with Ga + did not work and the only published compound which seemed likely to be asuitable starting material for coordination chemistry was the [Ga 2 Cp*] + cluster cation [5] -with the complication of providing one surplus equivalent of neutral GaCp* per used Ga + (Cp* = C 5 Me 5 ). Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers. [11] In all of this,[ Al-(OR F ) 4 ] À was very helpful [12] for the elimination of cation-anion interactions and allowed for ap redictable reaction outcome.H owever,d ue to its considerable size (diameter 1.25 nm, V À = 0.76 nm 3 )and the pseudo-gas-phase conditions that the anion provides, [8,13] the overall charge of such coordination compounds was expected to be limited to + 1.…”

Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2’-bipyridine

“…Our group introduced a simple route to univalent gallium and indium salts of the weakly coordinating [Al(OR F ) 4 ] − anion, by oxidizing elemental gallium and indium with Ag + [Al(OR F ) 4 ] − in fluorobenzene (C 6 H 5 F) 28 29 . Under inert conditions, the [M(C 6 H 5 F) 2 ] + [Al(OR F ) 4 ] − salts (M=Ga ( 1 ), In ( 2 )) are stable, soluble in aromatic solvents (preferably fluorinated), and a potent starting material for further Ga I and In I chemistry: for example, phosphine 29 , crown ether 30 , carbene 31 and N-heterocyclic arene 32 complexes. In addition, the [Ga(arene) 1-2 ] + complexes (arene=C 6 H 5 F, mesitylene, diphenylethane, m -terphenyl) are highly efficient isobutylene polymerization catalysts 33 34 .…”

The crystal structure of [Fe2(PIMIC6)(AnthCO2)(CH3CN)]·[Fe2(PIMIC6)(AnthCO2)(CH3CN)0.9(CH2Cl2)0.1]·[Fe2(PIMIC6)(AnthCO2)(OH2)]·0.75CH3CN: a crystallographer's nightmare or a fascinating case of disorder?

“…These disorders mainly involve anions or solvent molecules. Extreme examples of such anion disorders are described for gallium complexes with perfluorinated aluminium alkoxide anions (Lichtenthaler et al, 2015(Lichtenthaler et al, , 2014. Conversely, fully modeled complex disorders of organic ligands are rare among these structures because these large structures usually suffer from badly resolved or even nonresolvable disorders.…”