Experimental and theoretical identifications of the C3O2•••thiazole complex:: a stable pre-reactive intermediate

The structure and energy properties of the thiazole/C3O2 1:1 complex have been investigated in solid argon matrices using FT-infrared spectroscopy and ab initio Hartree-Fock, MP2 and density functional B3LYP calculations at the 6-31G** level. This complex trapped in argon matrices is characterised by a large shift of the asymmetric nu (cco) stretching mode to lower frequencies (Delta nu = 92.9 cm(-1)). Predicted frequency shifts for the T-Nu shaped structure were found to be in good agreement with the observed complex vibrational frequency shifts. This planar complex in which the C3O2 assumes a C-2 nu symmetry, is indicative of a nucleophilic attack of the nitrogen atom of the thiazole molecule on the C2 atom of the C3O2 moiety (d = 3.24, 3.04 and 3.39 Angstrom for the HF, MP2 and DF procedure, respectively). At the same time, we observed very short intermolecular distances, indicative of stabilising interactions between the oxygen atoms of the suboxide subunit and the 2 and 6 hydrogen atoms of thiazole, lying in the C3O2 plane. Examination of the T-Nu C-2 nu complex structure for the C3O2 subunit highlighted a pinching of the CCC (27.1, 28.9 and 17.6 degrees) and the CCO valence bond angles (2.7, 3.6 and 2.5 degrees) for the KF, MP? and DF procedures, respectively). The geometry of the complex and the structural modifications of the complex's suboxide moiety suggest there is a pre reactive intermediate of a nucleophilic addition. (C) 2001 Elsevier Science B.V. All rights reserved.