Elucidation of Structural Relationships and Assignment of¹H NMR Spectra of Transition-Metal Cyclidene Complexes by 2-D NMR Techniques

The complete¹H NMR spectra of five nickel cyclidene macrocyclic complexes are assigned by using DEPT (distortionless enhancement by polarization transfer) and 2-D NMR techniques: shift correlation, COSY (correlated shift), and NOESY (nuclear Overhauser enhanced correlated shift). The¹H NMR assignments are consistent with the complexes having an overall saddle shape with the two saturated six-membered rings (composed of nickel, two nitrogens, and a trimethylene chain) adopting a chair and a boat configuration similar to those observed in the X-ray crystal structures of these complexes. The¹H NMR spectra can distinguish between two possible configurations for the bridging moiety (lid-off and lid-on). The vinyl methyl groups, labeled as O and N, have a chemical shift separation greater than 0.35 ppm for a lid-off configuration and less than 0.15 ppm for a lid-on configuration. The complex [2,9,10,17,19,25,33,34-octamethyl-3,6,13,16,20,24,27,31-octaazapentacyclo[16.7.7.2⁸'¹¹.2³'⁶.2¹³'¹⁶]-octatriaconta-l,8,10,17,19,24,26,31,33-nonaene-k⁴N]nickel(II) hexafluorophosphate (V) has a bridge that consists of durene (tetramethylbenzene) supported by two piperazine rings. Those protons on the piperazine rings that are in close proximity to the arene ring are shifted upfield due to shielding contributions of the ring currents.