EFFECT OF COBALT-59 SELF-DECOUPLING ON THE SOLID-STATE P-31 CP MAS NMR-SPECTRA OF COBALOXIMES/

Phosphorus-31 NMR spectra of three solid cobaloxime complexes containi ng phosphorus donor ligands have been examined. At room temperature, t he P-31 CP/MAS NMR spectra of PBu(3)Co(DH)(2)Cl (I) are broad and rath er featureless, while PPh(3)Co(DH)(2)CH3 (II) and P(OEt)(3)Co(DH)(2)N- 3 (III) exhibit well-resolved eight-peak patterns which result from Co -59 (spin 7/2), P-31 spin-spin coupling. Variable temperature measurem ents on compound I indicate that the peak broadening observed at room temperature results from the onset of Co-59 self-decoupling. At 155 K, the Co-59 spin-lattice relaxation time is sufficiently long that well -resolved octets are observed. The experimental P-31 CP/MAS NMR spectr a were simulated using the first-order perturbation approach of Olivie ri and the information available from these simulations is discussed i n detail. The P-31 NMR spectra of compound I provide the first reporte d example of recoupling of the direct and indirect spin-spin interacti ons between a quadrupolar nucleus and a spin 1/2 nucleus in the solid state by means of low temperature CP/MAS NMR experiments.