Reaction of Binuclear Carboxylate Complexes of Molybdenum, Rhenium, Ruthenium, and Rhodium with tert-Butyl Isocyanide: Metal-Metal Bond Cleavage vs. Bond Retention

tert-Butyl isocyanide cleaves the quadruple metal-metal bonds in Mo2(O2CMe)4, Mo2(O2CCF3)4, or K4Mo2C18 to give the mononuclear, seven-coordinate species Mo(t-BuNC)5(O2CMe)2 or [Mo(t-BuNC)6X] [X], where X is o2CCF3 or Cl. These diamagnetic, 18-electron complexes may be converted into the known binary dication [Mo(t-BuNC)7] [PF6]2 by action of NH4PF6 and excess t-BuNC or into the polyoxoanion complex [Mo(t-BuNC)7][Mo6O19]-2Me2CO by recrystallization from acetone in air. The rhenium and ruthenium acetates, Re2(O2CMe)4Cl2 and Ru2(O2CMe)4Cl, are also cleaved by t-BuNC, yielding the mononuclear, six-coordinate species [Re(r-BuNC)6] [Cl] and tert-Ru(t-BuNC)4(O2CMe)2, respectively. In contrast, the singly bonded rhodium acetate, Rh2(O2CMe)4, reacts with t-BuNC to give the binuclear axial diadduct, Rh2(O2CMe)4(t-BuNC)2, where the metal-metal bond has been retained.