COMPETITIVE HYDROGEN-PRODUCTION AND EMISSION THROUGH THE PHOTOCHEMISTRY OF MIXED-METAL BIMETALLIC COMPLEXES

Preparation of the complexes RhH2(PPh3)2L+, [RhH2(PPh3)2]2L2+, and (bpy)2RuLRhH2(PPh3)23+ where L is 2,2′-bipyrimidine (bpm), 2,3-bis(2-pyridyl)pyrazine (dpp), and 2,3-bis(2-pyridyl)quinoxaline (dpq), as well as the monometallic analogues RhH2(PPh3)2en+ and RhH2(PPh3)2bpy+ (en = ethylenediamine and bpy = 2,2′-bipyridine) is described. All of the complexes undergo photochemically induced reductive elimination of molecular hydrogen when irradiated at wavelengths equal to or shorter than 405 nm for the monometallic complexes and equal to or shorter than 436 nm for the bimetallic complexes. In addition, the monometallic rhodium complexes and the heterobimetallic (RuLRh) complexes undergo emission in fluid solution at room temperature from a state different than the photoactive state. In the case of the heterobimetallic complexes, the photoemissive state is best described as a Ru-based metal-to-ligand charge-transfer (MLCT) state while the photoreaction is assigned as a Rh-based ligand-field (LF) state in all of the complexes studied. © 1990, American Chemical Society. All rights reserved.