Polynuclear transition metal complexes, which frequently constitute the active sites of both biological and chemical catalysts, provide access to unique chemical transformations that are derived from metal− metal cooperation. Reductive elimination via ligand-bridged binuclear intermediates from bimetallic cores is one mechanism by which metals may cooperate during catalysis. We have established families of Rh2 complexes that participate in HX-splitting photocatalysis in which metal−metal cooperation is credited with the ability to achieve multielectron photochemical reactions in preference to single electron transformations. Nanosecond-resolved transient absorption spectroscopy, steady-state photocrystallography, and computational modeling have allowed direct observation and characterization of Cl-bridged intermediates (intramolecular analogues of classical ligand-bridged intermediates in binuclear eliminations) in halogen elimination reactions. On the basis of these observations, a new class of Rh2 complexes, supported by CO ligands, has been prepared, allowing for the isolation and independent characterization of the proposed halide-bridged intermediates. Direct observation of halide-bridged structures establishes binuclear reductive elimination as a viable mechanism for photogenerating energetic bonds.
See: David C. Powers,† Bryce L. Anderson,† Seung Jun Hwang,† Tamara M. Powers,† Lisa M. Pérez,‡, Michael B. Hall,‡ Shao-Liang Zheng,† Yu-Sheng Chen,§ and Daniel G. Nocera*,† “Photocrystallographic Observation of Halide-Bridged Intermediates in Halogen Photoeliminations”, J. Am. Chem. Soc., 136 (43), 15346–15355 (2014).
Author Affiliations: †Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA, ‡Department of Chemistry, Texas A&M University, College Station, Texas, USA, §ChemMatCARS, The University of Chicago, Argonne, Illinois, USA.