Chemistry of CS₂ and CS₃ Bridged Decaborane Analogues: Regular Coordination Versus Cluster Expansion

In an effort to synthesize metallaheteroborane clusters of higher nuclearity, the reactivity of metallaheteroboranes, nido-[(Cp*M)₂B₆S₂H₄(CS₃)] (Cp* = C₅Me₅) (1: M = Co; 2: M = Rh) with various metal carbonyls have been investigated. Photolysis of nido-1 and nido-2 with group 6 metal carbonyls, M'(CO)₅.THF (M' = Mo or W) were performed that led to the formation of a series of adducts [(Cp*M)₂B₆S₂H₄(CS₃){M'(CO)₅}] (3: M = Co, M' = Mo; 4: M = Co, M' = W; 5: M = Rh, M' = Mo; 6: M = Rh, M' = W) instead of cluster expansion reactions. In these adducts, the S atom of C=S group of di(thioboralane)thione {B₂CS₃} moiety is coordinated to M'(CO)₅ (M = Mo or W) in η¹-fashion. On the other hand, thermolysis of nido-1 with Ru₃(CO)₁₂ yielded one fused metallaheteroborane cluster [{Ru(CO)₃}₃S{Ru(CO)}{Ru(CO)₂}Co₂B₆SH₄(CH₂S₂){Ru(CO)₃}₂S], 7. This 20-vertex-fused cluster is composed of two tetrahedral {Ru₃S} and {Ru₂B₂}, a flat butterfly {Ru₃S} and one octadecahedron {Co₂RuB₇S} core with one missing vertex, coordinated to {Ru₂SCH₂S₂} through two boron and one ruthenium atom. On the other hand, the room temperature reaction of nido-2 with Co₂(CO)₈ produced one 19-vertex fused metallaheteroborane cluster [(Cp*Rh)₂B₆H₄S₄{Co(CO)}₂{Co(CO)₂}₂(μ-CO)S{Co(CO)₃}₂], 8. Cluster 8 contains one nido-decaborane {Rh₂B₆S₂}, one butterfly {Co₂S₂} and one bicapped square pyramidal {Co₆S} unit that exhibits an intercluster fusion with two sulfur atoms in common. Clusters 3-6 have been characterized by multinuclear NMR and IR spectroscopy, mass spectrometry and structurally determined by XRD analyses. Furthermore, the DFT calculations have been carried out to gain insight into electronic, structural and bonding patterns of the synthesized clusters.