Square-Planar and Butterfly Tetranuclear Ruthenium Clusters Incorporating the Doubly Linked Bis(dimethylsilylcyclopentadienyl) Ligand

The doubly linked dicyclopentadienyl complex {(η5-C5H3)2(SiMe2)2}Ru2(CO)4 (1) reacts with
H2 in benzene under broad-spectrum UV−visible photolysis (254 < λirr < 600 nm) to give
the dinuclear {(η5-C5H3)2(SiMe2)2}Ru2(CO)4H2 (2) and the tetranuclear clusters {(η5-C5H3)2(SiMe2)2}2Ru4(CO)3H4 (3) with a butterfly structure and {(η5-C5H3)2(SiMe2)2}2Ru4(CO)4H4
(4) with a square-planar structure. The linked {(η5-C5H3)2(SiMe2)2} ligand is essential for
the formation of the tetranuclear clusters (3 and 4), as unlinked analogues, Cp‘2Ru2(CO)4,
give only di- and trinuclear products. Wavelength-dependent photolysis studies suggest that
the first step in the reaction of 1 with H2 involves metal−metal bond cleavage, which is
supported by the all-terminal CO ligand geometry of 1, the independent synthesis of 2, and
its photochemical reaction in the presence of H2 to give 3 and 4.