AN NMR INVESTIGATION OF 1,2-METALLOTROPIC SHIFTS IN TRANSITION-METAL COMPLEXES OF BENZO[C]CINNOLINE AND PYRIDAZINES

Complexes of types [W(CO)(5)L], [cis-Rh(CO)(2)C1L] (L = benzo[c]cinnoline) and [W(CO)(5)L'] (L' = pyridazine, 3-methylpyridazine, and 4-methylpyridazine) have been synthesized and shown to exhibit, in organic solvents, intramolecular metal-nitrogen 1,2-fluxional shifts, which have been quantitatively studied by ID bandshape analysis and 2D-EXSY NMR experiments. Energy barriers for the metallotropic shifts in the pyridazine complexes are ca. 20 kJ mol(-1) higher than in the benzo[c]cinnoline complexes. These differences are discussed in terms of the ground state and likely transition state species for this fluxional process.