Indium(III)/2-benzoylpyridine chemistry: interesting indium(III) bromide-assisted transformations of the ligand.

Reactions of 2-benzoylpyridine, (py)(ph)CO, with InX 3 (X = Cl, Br) in EtOH at room temperature have been studied. The InCl 3 /(py)(ph)CO system has provided access to complex [InCl 3 {(py)(ph)CO}(EtOH)]·{(py)(ph)CO} (1) and the byproduct {(pyH)(ph)CO}Cl (2). The reaction of InBr 3 with (py)(ph)CO has led to a mixture of (L)[InBr 4 {(py)(ph)CO}] (3) and [In 2 Br 4 {(py)(ph)CH(O)} 2 (EtOH) 2 ] (4), where L + is the 9-oxo-indolo[1,2- a ]pyridinium cation and (py)(ph)CH(O) - is the anion of (pyridin-2-yl)methanol. Based on solubility and crystallisation time differences between the two components of the mixture, complex 4 was isolated in pure form, i.e. free from 3. The formations of the counterion L + and the coordinated (py)(ph)CH(O) - anion represent clearly InBr 3 -promoted/assisted transformations. Reaction mechanisms have been proposed for the formation of 2, 3 and 4. Complex 4 could also be isolated by the reaction of InBr 3 and pre-formed (py)(ph)CH(OH) in EtOH. The solid-state structures of 1, 3 and 4 were determined by single-crystal X-ray crystallography, while the identity of the salt 2 was confirmed by microanalyses and a variety of spectroscopic techniques, including ESI-MS spectra. In the indium(III) complexes, the metal ions are 6-coordinate with a distorted octahedral geometry. The halogeno groups (Cl - , Br - ) in the three complexes are terminal. The (py)(ph)CO molecule behaves as a N,O-bidentate (1.11) ligand in 1 and 3. A terminal EtOH ligand completes the coordination sphere of In III in 1. The alkoxo oxygen atoms of the two 2.21 (py)(ph)CH(O) - ligands doubly bridge the In III centers in 4 creating a {InIII2(μ-OR) 2 } 4+ core; a nitrogen atom of one reduced organic ligand, two bromo ions and one terminal EtOH molecule complete the 6-coordination at each metal centre. Complexes 1, 3 and 4 were characterised by IR and Raman spectroscopies, and the data were discussed in terms of their known solid-state structures. Molar conductivity data and 1 H NMR spectra were used in an attempt to probe the behaviour of the complexes in DMSO. The to-date observed metal ion-assisted/promoted transformations of (py)(ph)CO are also discussed.