Third Generation Buchwald Precatalysts with XPhos and RuPhos: Multigram Scale Synthesis, Solvent-Dependent Isomerization of XPhos Pd G3 and Quality Control by 1H- and 31P-NMR Spectroscopy

The third generation Buchwald precatalysts Pd(ABP)(Phos)(OMs) (also known as Phos Pd G3)) with XPhos and RuPhos were prepared in multigram scale by a modified procedure (ABP = fragment of C-deprotonated 2-aminobiphenyl, XPhos = 2-dicyclohexylphosphino-2 ',4 ',6 '-triisopropylbiphenyl, RuPhos = 2-dicyclohexylphosphino-2 ',6 '-diisopropoxybiphenyl, OMs- = CH3SO3-). The H-1- and P-31-NMR spectra of the title complexes and some impurities, measured by various 1D and 2D techniques, were analyzed in detail. The solvent-dependent isomerization of Pd(ABP)(XPhos)(OMs) was studied by NMR, and the X-ray structures of two isomers were determined. The impurities in precatalysts, such as Pd(ABP)(HABP)(OMs) (HABP-neutral 2-aminobiphenyl coordinated to Pd2+ in N-monodentate mode) and PdCl2(XPhos)(2), were identified and characterized by single crystal X-ray diffraction. A simple method for the quick quality control (QC) of the precatalysts, suitable for routine use, was proposed. The method was based on the assessment of the impurity content on the basis of the H-1-NMR spectra analysis.

Automated summary

The study prepared third generation Buchwald precatalysts in multigram scale by a modified procedure and analyzed the structures of complexes and impurities using NMR. The solvent-dependent isomerization of a specific precatalyst was studied by NMR, and impurities were identified and characterized using single crystal X-ray diffraction. A simple method for quick quality control of the precatalysts based on H-1-NMR spectra analysis was proposed.