RHODIUM(I)-CENTERED CYCLOTRIVERATRYLENE

The rigid bowl-shaped molecule cyclotriveratrylene (CTV,1) was provide d with short and long spacer arms terminating in triphenyl phosphite f unctions. These CTV ligands were used to immobilize a rhodium(I)- carb onyl-hydride complex. The ligand with short spacers gave a rigid, stra ined complex with a trigonal-coordination sphere around the rhodium. T he ligand with long flexible spacers allowed the formation of a large cavity after the complexation to the rhodium center. This cavity, howe ver, is filled up by the spacer arms, as was indicated by NMR studies. Variable-temperature NMR experiments suggested that the H-Rh-CO dipol e in the rhodium-CTV complex can adopt two orientations: one with the hydride group pointing away from the CTV cavity (low-temperature confo rmation) and one in which this orientation is inverted (high-temperatu re conformation).