Reactions of 7-azaindole with niobium and tantalum pentachlorides and coupling to the azaindolyl-azaindolium cation

The reaction of NbCl 5 and TaCl 5 with 7-azaindole (Haza) at room temperature in benzene or dichloromethane yielded MCl 5 (Haza) addition compounds. Under more severe conditions, the same compound was obtained with TaCl 5 . For NbCl 5 , some reduction to Nb(IV) was observed and NbCl 5 (Haza), NbCl 4 (Haza) 2 , and the (H 2 aza) + ion were identified in the reaction mixture by infrared spectroscopy. Oxidative coupling of two azaindole units via N7C6 also took place during the reaction, since the 7-(azaindol-6-yl)azaindolium cation was found as counter-ion in the crystal structures of two complex salts. In the crystals of (H 2 aza-aza)[NbOCl 4 (Haza)]*0.5CH 2 Cl 2 ( a = 7.255 Å, b = 12.412 Å, c = 14.277 Å, α = 89.03°, β = 85.60°, γ = 76.66°, Z = 2, R = 0.062), the anion is the roughly octahedral [NbOCl 4 (azaindole)] − species containing a neutral N7-coordinated azaindole trans to the Nb=O bond. The [NbOCl 5 ] 2− salt ( a = 7.527 Å, b = 10.168 Å, c = 10.467 Å, α = 66.41°, β = 84.07°, γ = 85.51°, Z = 1, R = 0.037) contains the distorted octahedral [NbOCl 5 ] 2− ion disordered over two orientations. The infrared spectra suggest monomeric octahedral structures for the MCl 5 (Haza) and NbCl 4 (Haza) 2 complexes. 1 H NMR spectroscopy shows that NbCl 5 (Haza) is not dissociated in CD 2 Cl 2 .