Coordination Chemistry of Br₂InCH₂Br:  Coordination at the Metal Center

Abstract

(Bromomethyl)dibromoindium(III), Br2InCH2Br, reacts with tetraethylammonium bromide, 1,4-dioxane (diox), or tetrahydrofuran (thf) to produce addition compounds of the general formula Br2In(L) n CH2Br (L = diox, thf, n = 2; L = Br-, n = 1) in which the ligand is directly attached to the indium atom. The crystal structure of the ionic derivative [(C2H5)4N][Br3InCH2Br] has been solved by X-ray diffraction methods: cell constants a = 10.1710(1) Å, b = 10.1710(1) Å, and c = 35.1745(4) Å, space group P41212, V = 3638.78(7) Å3, Z = 8, R = 0.0519, R w = 0.0543 for 2374 independent reflections. Quantum mechanical calculations, by the PM3 method, on the parent molecule confirm the postulated strong intramolecular interaction between the bromomethylic bromine and the metal center. Complete intramolecular bromide transfer gives the tautomeric structure Br3Inδ-CH2 δ+. The calculations also satisfactorily predict the bond distances and angles in the Br3InCH2Br- anion. Preliminary investigations of the energetics and chemical properties of Br2In(diox)2CH2Br show that the molecule can decompose via elimination of methylene, which can be trapped by a suitable substrate (carboxylic acid, iodine), demonstrating the potential use of the compound as a methylene-transfer reagent.

Synthesis and molecular structures of dialkylselenonium methylide complexes of indium tribromide

“…[6], and the dialkyldisselenides, 2a-c react to afford the dialkylselenonium methylide-tribromo-indate(III) zwitterions, 3a-c (Scheme 2). The products were obtained as colorless solids from hot chloroform.…”

“…Ligand coordination to the metal is achieved by bromide anion and hard ligands, such as ethers and triphenylphosphine oxide [6]. The soft dialkylselenide ligands, R 1 SeR 2 coordinate to the soft halomethylic carbon of the carbenoid, forming the dialkylselenonium methylide adducts of indium tribromide, Br 3 InCH 2-SeR 1 R 2 .…”

“…Methylene bromide (Aldrich) was dried over Linde 4 Å molecular sieves. Br 2 In(diox) 2 CH 2 Br was prepared from InBr and CH 2 Br 2 as described earlier [6]. 1,4-Dioxane (diox) was dried over sodium and benzophenone, and distilled just before use from the blue ketyl form.…”

“…This analysis allows an interpretation of the reactivity of the X 2 InCH 2 X molecules in terms of the tautomeric relationship shown in Scheme 1 [6].…”

Dihalogen–halogenomethyl complexes of indium(III) X2InCH2X (X=Br, I): Simultaneous coordination of soft and hard ligands

“…While some of these compounds contain nucleophilic alkyl substituents capable of coupling to electrophiles [5][6][7]10,11], the methylene dihalide derivatives have been used mainly as models for coordination chemistry studies. Independently, we have determined that ligands with the hard donor atom oxygen, L H , such as ethers, dimethylsulfoxide and triphenylphosphine oxide coordinate to the metallic center of the Br 2 In(L H ) n CH 2 Br complex [12], while bases with soft donor atoms, L S , displace the bromine atom of the bromomethyl substituent to form corresponding ylides of InBr 3 of general structure Br 3 InCH 2 L S [13][14][15][16][17].…”