[Cp*Rh] hydride complexes are often invoked as key intermediates in a variety of catalytic cycles, but the chemical properties of such compounds remain poorly characterized. In this talk, we will describe the synthesis, isolation, and full characterization of two new [Cp*Rh] hydrides supported by the chelating diphosphine ligands bis(diphenylphosphino)methane (dppm) and 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos). Both dppm and Xantphos can be used to synthesize precursor Rh(III) complexes which undergo clean reduction with Na(Hg) to access isolable Rh(I) species. Building on our prior results with a Rh(I) complex supported by bis(diphenylphosphino)benzene, we find that addition of near-stoichiometric quantities of anilinium triflate results in high yields of the corresponding hydride complexes. Single-crystal X-ray diffraction data for these compounds provide evidence of direct Rh–H interactions; these are confirmed by complementary infrared spectra showing the Rh–H stretching frequencies at 1982 cm<sup>–1</sup> (dppm) and 1936 cm<sup>–1</sup> (Xantphos). Both of the synthesized hydrides feature unique, rich spin systems containing multiple NMR-active nuclei (Rh, P, H). Collection of multifrequency NMR data in concert with comprehensive simulations reveal that complex spectral splitting patterns for the hydride supported by dppm arise due to extensive coupling to the diastereotopic methylene protons. Taken together, our results support the robustness of the reduction/protonation sequence for preparation of [Cp*Rh] hydride complexes. In this presentation, the use of this powerful reaction sequence to prepare other new [Cp*Rh] hydride derivatives will also be discussed.

Modular and high-yielding synthesis of [Cp*Rh] hydrides via sequential reduction/protonation

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.