Synthesis of Bimetallic Dinuclear Hydrido Complexes of Re and Rh/Ir Supported by a Direct M–M′ Bond: The Role of the M–M′ Bond in the Site Exchange of Hydrides

Heterometallic tetrahydrido complexes [Cp*Re(H)₂(μ-H)₂MCp*] (5a: M = Ir, 5b: M = Rh) were synthesized by the reaction of [Cp*ReH₆] and [Cp*M(sol)₃]²⁺ (M = Ir, Rh) followed by deprotonation. Although 5 possesses four hydrides and adopts a 30-electron configuration as [Cp*Ru(μ-H)₄RuCp*] (1) does, the positions of the hydrides in 5 differ from those in 1: two terminal and two bridging hydrides. In addition, adaptive natural density partitioning (AdNDP) analysis demonstrated that a direct Re–M bond is held in 5. Although cationic pentahydrido complexes [Cp*Re(H)₂(μ-H)₃MCp*]⁺ (4a: M = Ir, 4b: M = Rh) do not contain a direct Re–M bond, the formation of a Re–M bond in the intermediate of the hydride site exchange was also inferred by DFT calculations. DFT calculations suggested that the Re–M bond plays a crucial role in the site exchange of hydrides in 5 and 4. While μ-phosphido complex [Cp*(PPh₃)Re(H)(μ-H)(μ-PPh₂)Ir(H)Cp*] (6) was obtained by the reaction of 5a with PPh₃, the treatment of 5a with PMe₃ resulted in the formation of a 1:1 mixture of [Cp*Re(H)₂(PMe₃)₂] and [Cp*Ir(H)₂PMe₃] via the rupture of the Re–Ir bond.