Molybdenum complexes with sterically demanding cycloheptatrienyl ligands

Sterically demanding tropylium salts of the type (1,3,5-C7H4R3)BF4 (3a, R = tert-butyl; 3b, R = isopropyl) and (C7H6R)BF4 (3c, R = tert-butyl; 3d, R = SiMe3) react with [(eta (6)-p-xylene)Mo(CO)(3)] by arene exchange and Mo(C O)(3) group transfer leading to cationic eta (7)-cycloheptatrienyl complexe s 4a-4d in excellent yields. 4a further reacts with alkali halides to give [(eta (7)-1,3,5-C7H4R3)Mo(CO)(2)X] (5a, R = tert-butyl, X = Cl; 6a, R = ter t-butyl, X = I). The X-ray crystal structures of 1,3,5-tri-tert-butyltropyl ium tetrafluoroborate (3a) and of [(n(7)-1,3,5-C7H4R3)Mo(CO)(3)]BF4 (4a, R = tert-butyl) are reported.