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 (CO)-C-13-labeled Ir(I) complex bearing an P,N-donor ligand (1-[2-(diphenylphosphino)ethyl]pyrazole), [Ir(PyP)((CO)-C-13)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 H-1 MAS and 2D C-13 and P-31 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 (H-1-C-13 HETCOR, H-1-P-31 correlation) to characterize the networks of dipolar couplings between protons and carbon/phosphorus. H-1-H-1 SQ-SQ correlation spectra showed the dipolar contacts between all protons in a similar fashion to its solution counterpart, NOESY. The use of the H-1 single quantum/double quantum experiments made it possible to observe the dipolar-coupling contacts between immediately adjacent protons. Additionally, internuclear (CO)-C-13-P-31 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)((CO)-C-13)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.