Synthesis of Cubic [Mo₃S₄M] (M = Rh, Ir) Clusters for the Borylation of C–H Bonds in Aromatic Compounds

The incorporation of Rh or Ir into the [Mo₃S₄] platforms of [[XL]Cp₃Mo₃S₄] or [Cp*₃Mo₃S₄] ([XL]Cp = C₅Me₄SiEt₃, Cp* = C₅Me₅) led to the formation of cubic [Mo₃S₄M] clusters, [[XL]Cp₃Mo₃S₄Rh(cod)] (1), [[XL]Cp₃Mo₃S₄Ir(coe)] (2), [Cp*₃Mo₃S₄Rh(coe)] (3), and [Cp*₃Mo₃S₄Ir(coe)] (4) (cod = 1,5-cyclooctadiene, coe = cyclooctene). These clusters were characterized spectroscopically and crystallographically. They catalyzed the C–H borylation of aromatic compounds (benzene, toluene, o-xylene, m-xylene, and p-xylene) in the presence of HBpin (4,4,5,5-tetramethyl-1,3,2-dioxaborolane), yielding the corresponding borylated products. Among these, cluster 3 exhibited the highest catalytic activity, while the treatment of cluster 2 with excess HBpin generated a millisecond-detectable potential intermediate, [[XL]Cp₃Mo₃S₄Ir(Bpin)]⁺. Despite the high affinity of Lewis acidic boron toward sulfur, the robust [Mo₃S₄M] (M = Rh, Ir) cubes protected adequately by Cp ligands have proven effective in borylation chemistry.