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

The structure and energy properties of the thiazole/C3O2 1:1 complex have b een investigated in solid argon matrices using FT-infrared spectroscopy and ab initio Hartree-Fock, MP2 and density functional B3LYP calculations at t he 6-31G** level. This complex trapped in argon matrices is characterised b y a large shift of the asymmetric nu (cco) stretching mode to lower frequen cies (Delta nu = 92.9 cm(-1)). Predicted frequency shifts for the T-Nu shap ed structure were found to be in good agreement with the observed complex v ibrational frequency shifts. This planar complex in which the C3O2 assumes a C-2 nu symmetry, is indicative of a nucleophilic attack of the nitrogen a tom 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 t he same time, we observed very short intermolecular distances, indicative o f 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 highl ighted a pinching of the CCC (27.1, 28.9 and 17.6 degrees) and the CCO vale nce bond angles (2.7, 3.6 and 2.5 degrees) for the KF, MP? and DF procedure s, 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 nucleo philic addition. (C) 2001 Elsevier Science B.V. All rights reserved.