Structural Insights from ⁵⁹Co Solid‐State NMR Experiments on Organocobalt(I) Catalysts

Abstract

A series of fumarate-based organocobalt(I) [CoCp(CO)(fumarate)] catalysts is synthesized and characterized by X-ray crystallography, multinuclear ( C and Co) solid-state NMR spectroscopy, and Co NQR spectroscopy. Given the dearth of Co solid-state NMR studies on Co compounds, the present work constitutes the first systematic characterization of the Co electric field gradient and chemical shift tensors for a series of cobalt complexes in this oxidation state. Using X-ray crystallography, the molecular geometry about the Co centre is found to be nearly identical in all compounds studied herein. Owing to the Co nucleus' large chemical shift range, solid-state NMR experiments are found to be able to detect small structural differences between the individual organocobalt(I) compounds. With the aid of density functional theory calculations on these complexes, it is shown that the Co chemical shift anisotropy and the Co quadrupolar coupling constant are both extremely sensitive gauges of the Fu-Co-Cp bond angle, providing a link between these Co NMR observables and the catalysts' structures.

Electron and Spin Delocalization in [Co6Se8(PEt3)6]0/+1 Superatoms

“…To put these results in context, in Table S7, we survey the isotropic chemical shifts of a series of Co(III) and Co(I) compounds. [37][38][39][40][41][42][43] (NMR data for Co(II) are rare since Co(II) compounds are paramagnetic.) The isotropic chemical shift of Co 6 Se 8 (PEt 3 ) 6 has an intermediate value, suggesting that the 59 Co is in a delocalized system.…”

“…(SI text) With C Q at 25±2 MHz, this second‐order term is small compared to J‐coupling, consistent with our observation of J‐coupling resolved 31 P spectrum and narrow linewidth. To put these results in context, in Table S7, we survey the isotropic chemical shifts of a series of Co(III) and Co(I) compounds [37–43] . (NMR data for Co(II) are rare since Co(II) compounds are paramagnetic.)…”

Molecular Magnetic Materials Based on {CoIII(Tp*)(CN)3}− Cyanidometallate: Combined Magnetic, Structural and 59Co NMR Study

“…The NMR line shapes in 1 – 3 suffer from an expected quadrupolar broadening. Only the compound 1 has been simulated and estimates of the quadrupolar coupling parameters were obtained [10b,d] . Note that these simulations cannot be carried out for 2 and 3 .…”

A Quadrupole‐Central‐Transition 59Co NMR Study of Cobalamins in Solution

“…successfully detected 59 Co NMR signals from a single‐crystal sample of CNCbl. However, while solid‐state 59 Co NMR has proven useful for studying small molecules, biological macromolecules larger than Cbl have appeared to be out of reach to date.…”