Solid-state NMR structure characterization of a ¹³CO-labeled Ir(I) Complex with a P, N -donor ligand including ultrafast MAS methods

The structural characterization of a ¹³CO-labeled Ir(I) complex bearing an P,N-donor ligand (1-[2-(diphenylphosphino)ethyl]pyrazole), [Ir(PyP)(¹³CO)Cl] is demonstrated using a series of tailored solid-state NMR techniques based on ultrafast (60 kHz) Magic Angle Spinning (MAS), which facilitates correlations with narrow proton line-widths. Our 1D ¹H MAS and 2D ¹³C and ³¹P CP-MAS NMR spectra provided structural information similar to that obtained using NMR spectroscopy in solution. We employed high-resolution 2D solid-state correlation spectroscopy (¹H-¹³C HETCOR, ¹H-³¹P correlation) to characterize the networks of dipolar couplings between protons and carbon/phosphorus. ¹H-¹H SQ-SQ correlation spectra showed the dipolar contacts between all protons in a similar fashion to its solution counterpart, NOESY. The use of the ¹H single quantum/double quantum experiments made it possible to observe the dipolar-coupling contacts between immediately adjacent protons. Additionally, internuclear ¹³CO- ³¹P distance measurements were performed using REDOR. The combination of all of these techniques made it possible to obtain comprehensive structural information on the molecule [Ir(PyP)(¹³CO)Cl] in the solid state, which is in excellent agreement with the single crystal X-ray structure of the complex, and demonstrates the enormous value of ultrafast MAS NMR techniques for a broad range of future applications.