Unique Oxidative Metal−Metal Bond Formation of Linearly Aligned Tetranuclear Rh−Mo−Mo−Rh Clusters

Reaction of Mo2(pyphos)4 (1) with [RhCl(CO)2]2 followed by treatment of excess amounts of tBuNC resulted in the clean formation of [Mo2Rh2(tBuNC)4(pyphos)4](X)2 (4a; X = Cl). The X-ray diffraction study as well as spectroscopic analyses of 4c (X = BPh4) implied that there is no direct σ-bonding interaction between each Rh(I) atom and the Mo2 core. Each Rh(I) atom in 4 can be oxidized concurrently by 2 equiv of [Cp2Fe]PF6 to afford [Mo2Rh2(Cl)2(tBuNC)4(pyphos)4](PF6)2 (5) along with the formation of two Mo−Rh(II) single bonds and the reduction of the bond orders of the Mo−Mo moiety.