Structural and Crystallographic Information from ⁶¹Ni Solid-State NMR Spectroscopy: Diamagnetic Nickel Compounds

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Nickel-61 (61Ni) NMR spectroscopy is underdeveloped, especially in the solid state.
• Previous solid-state NMR studies on nickel were limited to metals and intermetallics.
• Nickel(0) compounds have been studied by 61Ni NMR in solution, but solid-state data is scarce.

Purpose of the Study:

• To report the first 61Ni solid-state NMR (SSNMR) spectra of diamagnetic nickel(0) compounds.
• To characterize specific nickel(0) complexes using 61Ni SSNMR.
• To propose a safer secondary chemical shift reference for 61Ni NMR.

Main Methods:

• Utilized 61Ni SSNMR spectroscopy on bis(1,5-cyclooctadiene)nickel(0) [Ni(cod)2], tetrakis(triphenylphosphite)nickel(0) [Ni[P(OPh)3]4], and tetrakis(triphenylphosphine)nickel(0) [Ni(PPh3)4].
• Performed solution-state 61Ni NMR studies on Ni(cod)2.
• Conducted relativistic computations and ligand NMR studies alongside 61Ni SSNMR.

Main Results:

• Determined key NMR parameters (isotropic chemical shift, span, skew, quadrupolar coupling constant, asymmetry parameter) for Ni(cod)2 in solid and solution states.
• Identified two distinct crystallographic sites for Ni[P(OPh)3]4 and established solid-state NMR parameter ranges.
• Obtained 61Ni SSNMR parameters for Ni(PPh3)4, demonstrating the technique's utility for compounds lacking crystal structures or solution stability.
• Proposed Ni(cod)2 solution as a safer secondary 61Ni NMR reference.

Conclusions:

• Successfully obtained and analyzed the first 61Ni SSNMR spectra for diamagnetic nickel(0) compounds.
• Established Ni(cod)2 solution as a viable secondary chemical shift reference for 61Ni NMR.
• Highlighted the potential of 61Ni SSNMR for characterizing nickel complexes, even those with limited structural or solution data.