Novel Sterically Congested Monoorganobismuth(III) Compounds: Synthesis, Structure, and Bismuth−Arene π Interaction in ArBiXY (X, Y = Br, I, OH, 2,6-Mes₂-4-t-Bu-C₆H₂PHO₂)

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.