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*] (<b>5a</b>: M = Ir, <b>5b</b>: M = Rh) were synthesized by the reaction of [Cp*ReH₆] and [Cp*M(sol)₃]²⁺ (M = Ir, Rh) followed by deprotonation. Although <b>5</b> possesses four hydrides and adopts a 30-electron configuration as [Cp*Ru(μ-H)₄RuCp*] (<b>1</b>) does, the positions of the hydrides in <b>5</b> differ from those in <b>1</b>: two terminal and two bridging hydrides. In addition, adaptive natural density partitioning (AdNDP) analysis demonstrated that a direct Re-M bond is held in <b>5</b>. Although cationic pentahydrido complexes [Cp*Re(H)₂(μ-H)₃MCp*]⁺ (<b>4a</b>: M = Ir, <b>4b</b>: 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 <b>5</b> and <b>4</b>. While μ-phosphido complex [Cp*(PPh₃)Re(H)(μ-H)(μ-PPh₂)Ir(H)Cp*] (<b>6</b>) was obtained by the reaction of <b>5a</b> with PPh₃, the treatment of <b>5a</b> 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.