Reactivity and Mechanisms of Photoactivated Heterometallic [RuII NiII ] and [RuII NiII RuII ] Catalysts for Dihydrogen Generation from Water.

Two heterometallic photocatalysts were designed and probed for water reduction. Both [(bpy)2 RuII NiII (L1 )](ClO4 )2 (1) and [(bpy)2 RuII NiII (L2 )2 RuII (bpy)2 ](ClO4 )2 (2) can generate the low-valent precursor involved in hydride formation prior to dihydrogen generation. However, while the bimetallic [RuII NiII ] (1) requires the presence of an external photosensitizer to trigger catalytic activity, the trimetallic [RuII NiII RuII ] (2) displays significant coupling between the catalytic and light-harvesting units to promote intramolecular multielectron transfer and perform photocatalysis at the Ni center. A concerted experimental and theoretical effort proposes mechanisms to explain why 1 is unable to achieve self-supported catalysis, while 2 is fully photocatalytic.

2-Chloro-3-[(2-oxo-2H-chromen-6-yl)amino]-naphthalene-1,4-dione.

In the title compound, C19H10ClNO4, the dihedral angle between the naphtho-quinone and coumarin rings is 48.99 (6)°. In the crystal, mol-ecules are linked by strong N-H⋯O hydrogen bonds into chains with graph-set motif C(6) along [101]. The packing also features π-π stacking inter-actions between naphtho-quinone and coumarin rings [centroid-to-centroid distances = 3.7679 (12) and 3.6180 (13) Å].