Assembled Porphyrin-Based Multinuclear Ruthenium(II)-NNNN Complex Catalysts for Transfer Hydrogenation of Ketones

Multinuclear porphyrin-based ruthenium(II)-NNNN complexes were efficiently assembled by means of coordinatively unsaturated 16-electron mononuclear ruthenium(II)-pyrazolyl-imidazolyl-pyridine complex, zinc(II) meso-tetra(4-pyridyl)-porphyrin (ZnTPyP), and 4,4′-linked bipyridines. The resultant multinuclear (Ru₄ and Ru₈) porphyrin-based ruthenium(II)-NNNN complexes exhibited exceptionally high catalytic activity at as low as 0.008 mol % Ru loading for the transfer hydrogenation reaction of ketones in refluxing 2-propanol, reaching up to 99 % yields and 5.7×10⁶ h⁻¹ TOFs.