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 sigma-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.