“Crowned” Univalent Indium Complexes as Donors? Experimental and Computational Insights on the Valence Isomers of EE′X₄ Species

Abstract

The use of the univalent indium reagent [In([18]crown-6)][OTf] as a donor is investigated by its reactions with acceptors including InX(3) (X=Cl, Br, I). The donor-acceptor complexes of the form [X([18]crown-6)In-InX(3)] obtained in this manner represent the first new isomeric form of indium(II) halides identified for at least five decades. The formation of such complexes appears to be particularly favorable and they are isolated as products in many reactions involving low-valent indium, a halide source, and [18]crown-6. A convenient solution-phase synthesis of In[ECl(4)] salts is reported. This facile and direct syntheses of In[ECl(4)] (E=Al, Ga, In) salts allows for the in situ preparation and isolation of crown-ether complexes of the form [In([18]crown-6)][ECl(4)], whose existence had been postulated but never confirmed. Solution-phase and solid-state NMR experiments reveal that these compounds can exist as either donor-acceptor complexes or ionic salts, depending on the phase of the system, the nature of the solvent employed, and the identity of the metalate anion involved. Similar investigations into the effect of a smaller crown ether allow for the isolations of salts containing the cation [In([15]crown-5)](+). Computational investigations into the nature of the crowned univalent indium donor fragments, and on the donor-acceptor complexes produced, demonstrate the influence of anionic substituents on the reactivity of lone pair of electrons of the In(I) center. Natural bond orbital (NBO) analysis of donor-acceptor models shows that the composition of the E-E bond MO should provide the ability to predict which models should form stable complexes.

Univalent Gallium and Indium Phosphane Complexes: From Pyramidal M(PPh3)3+ to Carbene‐Analogous Bent M(PtBu3)2+ (M=Ga, In) Complexes

“…Similar shifts were reported for a solution of In/GaCl 3 /benzene of not entirely characterized content (d = À1350 ppm) [37,38] and InA C H T U N G T R E N N U N G [AlCl 4 ] in benzene (d = 1264 ppm). [39] The shift of the related-but structurally different-InA C H T U N G T R E N N U N G [OTf] in MeCN was found by Cooper and Macdonald to be d = À1053 ppm. [24] 115 In NMR shifts of In III compounds may be extrapolated from known 71 Ga NMR shifts of homologous compounds.…”

Non‐Innocent Ligand Effects on Low‐Oxidation‐State Indium Complexes

“…As previously noted, Richeson et al. find very little covalent interaction between diiminopyridine ligands and the indium centers in their dimpy complexes and proposed that a lower 5 s orbital contribution to the HOMO of the diiminopyridine complex is consistent with a more stable molecule 29. 35, 46…”

“…As previously noted, Richeson et al find very little covalent interaction between diiminopyridine ligands and the indium centers in their dimpy complexes and proposed that a lower 5 s orbital contribution to the HOMO of the diiminopyridine complex is consistent with a more stable molecule. [29,35,46] Herein, we employ natural bond order (NBO) analyses, Wiberg bond indices (WBI), and geometrical analyses in an effort to rationalize the similarities and differences observed experimentally between the closely related diimine complexes described above.…”

“…[25] Likewise, attempts to incorporate inA C H T U N G T R E N N U N G di-A C H T U N G T R E N N U N G um(I) halides into cyclic ether ligands at room temperature resulted in the formation of mixed-valent In I -In III donor-acceptor complexes. [29] In contrast to the univalent halides, we have previously shown that the more stable indium(I) triflate, InOTf, [30][31] can form a monomeric donor-stabilized species in the pres-ence of appropriate ligands. [32][33] Although treatment of InOTf with tmeda results in immediate disproportionation, the reaction with crown ethers produces remarkably robust species.…”

A115In solid-state NMR study of low oxidation-state indium complexes

“…indium site; however, the C Q is much smaller than that of [In([18]crown-6)][OTf], implying that structural arrangements similar to this are unlikely. Given that the[18]crown-6 cavity is large enough to accommodate the In(I) ion,76 and given that interactions between the tetrachloride ions and indium are a possibility (and would certainly result in a reduced C Q compared to [In([18]crown-6)][OTf]), we propose the structural model pictured in Scheme 1(g). The presence of GaCl 4 and AlCl 4 are confirmed by71 Ga and27 Al SSNMR spectra (…”