Four novel sterically congested terphenyl-substituted bismuth dihalides of the type [2,6-Mes 2 -4-R-C 6 H 2 BiX 2 ] 2 (1, R ) t-Bu, X ) Cl, Br; 2, R ) H, X ) Br; 3, R ) t-Bu, X ) Br; 4, R ) H, X ) I) were synthesized and structurally characterized including single-crystal X-ray diffraction analyses. Whereas the compounds 1-3 are dimeric in the solid state, the organobismuth diiodide 4 is a one-dimensional coordination polymer. Upon hydrolysis of compound 3, the first structurally characterized monoorganobismuth halide hydroxide, [2,6-Mes 2 -4-t-Bu-C 6 H 2 BiBr(OH)] 2 (5), was isolated instead of the expected monoorganobismuth dihydroxide. Stability of compound 5 toward further hydrolysis might be interpreted to be the result of both intramolecular bismuth-arene π interaction and intramolecular OH-arene π interaction. Reaction of compound 5 with the sterically congested phosphinic acid 2,6-Mes 2 -4-t-Bu-C 6 H 2 PH(O)(OH) gave the organobismuth phosphinate ArBiBrO(O)HPAr (Ar ) 2,6-Mes 2 -4-t-Bu-C 6 H 2 ) (6). The single-crystal X-ray structure analysis of compound 6 reveals unusual 2-fold intramolecular bismuth-arene coordination. Compounds 3, 5, and 6 were studied in detail by temperature-dependent NMR spectroscopy in solution in order to get information on the Menshutkin-like bismuth-arene π interaction. Whereas for compounds 3 and 5 only qualitative information was obtained showing that the dimeric structures most likely are not preserved in solution, more distinct information was available for compound 6. Four distinct intramolecular processes were observed. The energy barriers for the dislocation of the arene ligands in compound 6 by rotation of the terphenyl ligand around the Bi-C bond was estimated to be approximately 54 kJ mol -1 . This energy barrier results from a combination of both steric hindrance for the rotation and intramolecular bismuth-arene π complexation.

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