Coordination Chemistry of Br 2 InCH 2 Br: Coordination at the Metal Center Antonio B. de Carvalho, Maria A. M. A. de Maurera, Jose ´ A. Nobrega, and Clovis Peppe* Departamento de Quimı ´ca, CCEN, Universidade Federal da Paraı ´ba, Campus I, Joa ˜ o Pessoa-PB, Brazil 58059-900 Martyn A. Brown and Dennis G. Tuck Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Marcelo Z. Hernandes, Elson Longo, and Fabricio R. Sensato Departamento de Quimı ´ca, Universidade Federal de Sa ˜ o Carlos, Sa ˜ o Carlos-SP, Brazil 13565-905 Received July 30, 1998 (Bromomethyl)dibromoindium(III), Br 2 InCH 2 Br, reacts with tetraethylammonium bromide, 1,4-dioxane (diox), or tetrahydrofuran (thf) to produce addition compounds of the general formula Br 2 In(L) n CH 2 Br (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 [(C 2 H 5 ) 4 N][Br 3 - InCH 2 Br] 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 P4 1 2 1 2, V ) 3638.78(7) Å 3 , 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 intramo- lecular bromide transfer gives the tautomeric structure Br 3 In δ- CH 2 δ+ . The calculations also satisfactorily predict the bond distances and angles in the Br 3 InCH 2 Br - anion. Preliminary investigations of the energetics and chemical properties of Br 2 In(diox) 2 CH 2 Br 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. Introduction In the past few years, some important organic trans- formations mediated by indium compounds have been reported. 1 Relevant examples include the Barbier ally- lation, 2 the Reformatsky reaction, 2 and the epoxidation of carbonyl compounds. 3 A common feature of these three processes is the presence of a donor group, directly attached to the haloalkyl carbon atom of the corres- ponding reagent, and a probable initial step in these transformations is that shown in Scheme 1, involving the oxidative insertion of the indium(I) halide, InX (X ) Cl, Br), at the carbon-halogen bond of the organic reagent. This is in keeping with our earlier finding that InX inserts into the carbon-halogen bonds of alkyl halides, 4,5 dihalides, 6 and trihalides. 7,8 The key step in all these reactions is a strong interaction between the R-donor groups and the metal center, giving an inter- mediate which reacts readily with carbonyl compounds. During the past few years, we have also examined the interactions of R-donor groups with the metal center of organoindium(III) compounds. We have demon- strated 6 that the bromomethyl compound Br 2 InCH 2 Br can be prepared by the oxidative insertion of indium(I) bromide into the carbon-bromine bond of methylene dibromide, and the coordination chemistry of Br 2 InCH 2 - Br is being extensively explored. The addition of a neutral ligand L (L ) N,N,N′,N′-tetramethylethanedi- (1) Cintas, P. Synlett 1995, 1087. (2) Araki, S.; Ito, H.; Katsumura, N.; Butsugan, Y. J. Organomet. Chem. 1989, 369, 291. (3) Araki, S.; Butsugan, Y. J. Chem. Soc., Chem. Commun. 1989, 1286. (4) Peppe, C.; Tuck, D. G.; Victoriano, L. J. Chem. Soc., Dalton Trans. 1982, 2165. (5) Khan, M. A.; Peppe, C.; Tuck, D. G. J. Organomet. Chem. 1985, 280, 17. (6) Annan, T. A.; Tuck, D. G.; Khan, M. A.; Peppe, C. Organome- tallics 1991, 10, 2159. (7) dos Santos, J. E.; Peppe, C.; Tuck, D. G. Organometallics 1996, 15, 2201. (8) Nobrega, J. A.; Peppe, C.; Brown, M. A.; Tuck, D. G. Chem. Commun. 1998, 381. Scheme 1 99 Organometallics 1999, 18, 99-105 10.1021/om980656p CCC: $18.00 © 1999 American Chemical Society Publication on Web 12/11/1998