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

Heterometallic tetrahydrido complexes\n[Cp*Re(H)<sub>2</sub>(μ-H)<sub>2</sub>MCp*] (<b>5a</b>: M = Ir, <b>5b</b>: M = Rh) were\nsynthesized by the reaction of [Cp*ReH<sub>6</sub>] and [Cp*M(sol)<sub>3</sub>]<sup>2+</sup> (M = Ir, Rh) followed by deprotonation. Although <b>5</b> possesses four hydrides and adopts a 30-electron configuration\nas [Cp*Ru(μ-H)<sub>4</sub>RuCp*] (<b>1</b>) does, the\npositions of the hydrides in <b>5</b> differ from those in <b>1</b>: two terminal and two bridging hydrides. In addition, adaptive\nnatural density partitioning (AdNDP) analysis demonstrated that a\ndirect Re–M bond is held in <b>5</b>. Although cationic\npentahydrido complexes [Cp*Re(H)<sub>2</sub>(μ-H)<sub>3</sub>MCp*]<sup>+</sup> (<b>4a</b>: M = Ir, <b>4b</b>: M =\nRh) do not contain a direct Re–M bond, the formation of a Re–M\nbond in the intermediate of the hydride site exchange was also inferred\nby DFT calculations. DFT calculations suggested that the Re–M\nbond plays a crucial role in the site exchange of hydrides in <b>5</b> and <b>4</b>. While μ-phosphido complex [Cp*(PPh<sub>3</sub>)Re(H)(μ-H)(μ-PPh<sub>2</sub>)Ir(H)Cp*] (<b>6</b>) was obtained by the reaction of <b>5a</b> with PPh<sub>3</sub>, the treatment of <b>5a</b> with PMe<sub>3</sub> resulted\nin the formation of a 1:1 mixture of [Cp*Re(H)<sub>2</sub>(PMe<sub>3</sub>)<sub>2</sub>] and [Cp*Ir(H)<sub>2</sub>PMe<sub>3</sub>] via\nthe rupture of the Re–Ir bond.