Nuclear Magnetic Resonance Spectroscopy. Observation of Carbon-13 Resonances in a Paramagnetic Transition Metal Complex. Nickel(II) N,N'-di(p-tolyl)aminotroponiminate

The discovery of the extraordinary chemical shifts of the proton magnetic resonances of paramagnetic Ni(II) aminotroponiminates has been of great value for probing the nature of metal-ligand bonding especially because sharp resonances are observed as the result of the short electronic relaxation times of the tetrahedral forms which are associated with the squareplanar (diamagnetic) ⇌ tetrahedral (paramagnetic) equilibria. These complexes are expected to provide a useful starting point for natural-abundance nmr studies of paramagnetic transition metal complexes. We report in this study observation of eight of the possible nine carbon resonances of the N,N’-di(ptolyl) derivative 1, and present evidence for nonzero spin density in the σ framework of the ligand