Room temperature reaction of K(2)[Ru(3)(CO)(11)] with the molybdenum(VI) bis(imido) complexes Mo(NAr)(2)Cl(2)(dme) (Ar = C(6)H(3)X(2)-2,6; X = Me, Pr(i), Cl; dme = 1,2-dimethoxyethane) affords new high-low valent clusters Ru(3)(CO)(12){Mo(NAr)(2)} which adopt a butterfly arrangement of metal centres with [Ru(3)(CO)(12)](2-) acting as a ligand at a molybdenum(VI) centre.