Atom-economical synthesis of 1,2-bis(phosphine oxide)ethanes from calcium carbide with straightforward access to deuterium- and 13C-labeled bidentate phosphorus ligands and metal complexes

Abstract

Stable and easily detectable isotopic labels provide advanced opportunities in a wide range of chemical applications. Highly specific information can be retrieved upon analysis of isotopic label movement from one position to another. The incorporation of isotopic labels into organic molecules is in high demand; however, it may often be rather challenging. The introduction of D and ¹³C labels is of particular interest due to authentic signals in NMR spectra and the reliable identification of isotopic label positions in target molecules. In this work, a convenient methodology for the introduction of D and ¹³C labels was developed using calcium carbide as a source of D- and ¹³C-labeled acetylene and phosphine oxides as substrates. As a result, d₄- and ¹³C₂-1,2-bis(phosphine oxide)ethanes were isolated in yields and isotopic purities up to 99%. The resulting phosphine oxides were reduced to the corresponding phosphines, which were used as ligands for the preparation of D-labeled Ni and Pd complexes in 80–96% yields with further characterization by NMR spectroscopy, X-ray and HRMS. The incorporation of D and ¹³C labels using calcium carbide and acetylene is of key importance since atom-economical addition reactions can be involved with intrinsic opportunity for saving valuable isotopic labels.