Mixed-metal chalcogenide tetrahedral clusters with an exo-polyhedral metal fragment.

The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(µ-H){Os3(CO)9}S], 3, and [Cp*Ru(µ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(µ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(µ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and (1)H, (11)B and (13)C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6.

Metallaboranes from Metal Carbonyl Compounds and Their Utilization as Catalysts for Alkyne Cyclotrimerization.

The photolysis of [M2 (CO)10 ] (M=Re or Mn) with BH3 ⋅thf at room temperature yields arachno-1 and 2, [(CO)8 M2 B2 H6 ] (1: M=Re, 2: M=Mn). Both the compounds show a butterfly structure with seven skeletal electron pairs and 42 valence electrons. This result presents a new method for general access to low-boron-content metal-boron compounds without the cyclopentadienyl ligand at the metal centers. This new synthetic route is superior to the existing procedures because it avoids the use of [LiBH4 ] and metal polychlorides, for which the synthesis is very tedious. Compound 1 catalyzes the cyclotrimerization of a series of internal and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivity of 1 with alkynes demonstrates for the first time that the introduction of the [B2 H6 ] moiety into the [Re2 (CO)10 ] framework significantly enhances the catalytic activity. Note that [Re2 (CO)10 ] catalyzes the same set of alkynes under harsh conditions over a prolonged period of time. Quantum-chemical calculations using DFT methods are applied to afford further insight into the electronic structure, stability, and bonding of 1 and 2. All the compounds are characterized by IR and 1 H, 11 B, and 13 C NMR spectroscopy, and the geometry of 1 is established unambiguously through crystallographic analysis.