Cluster Growth Reactions: Structures and Bonding of Metal-Rich Metallaheteroboranes Containing Heavier Chalcogen...

In an effort to synthesize cobalt-rich metallaheteroboranes from decaborane(14) analogues, we have studied the reaction of 10-vertex nido-[(Cp*Co)₂B₆H₆E₂] (Cp* = η⁵-C₅Me₅, 1: E = Se and 2: E = Te) with [Co₂(CO)₈] under thermolytic conditions. All of these reactions yielded face-fused clusters, [(Cp*Co)₂B₆H₆E₂{Co(CO)}(μ-CO){Co₃(CO)₆}] (3: E = Se and 4: E = Te). Further, when clusters 3 and 4 were treated with [Co₂(CO)₈], they underwent further cluster buildup reactions leading to the formation of 16-vertex doubly face-fused clusters [(Cp*Co)₂B₆H₆E₂{Co₂(CO)₂}(μ-CO)₂{Co₄(CO)₈}] (5: E = Se and 6: E = Te). Cobaltaheteroboranes 3 and 4 comprise one icosahedron {Co₄B₆E₂} and one square pyramidal {Co₃B₂} moiety, whereas 5 and 6 are made with one icosahedron {Co₄B₆E₂} and two square pyramidal {Co₃B₂} cores. In an attempt to generate heterometallic metal-rich clusters, we have explored the reactivity of decaborane(14) analogue nido-[(Cp*Co)₂B₇TeH₉] (7) with [Ru₃(CO)₁₂] at 80 °C, which afforded face-fused 13-vertex cluster [(Cp*Co)₂B₇H₇Te{Ru₃(CO)₈}] (8). Cluster 8 is a rare example of a metal-rich metallaheteroborane in which one icosahedron {Co₂Ru₂B₇Te} and a tetrahedron {Ru₂B₂} units are fused through a common {RuB₂} triangular face. Further, the treatment of nido-[(Cp*Co)₂B₆S₂H₄(CH₂S₂)] (9) with [Fe₂(CO)₉] afforded 11-vertex nido-[(Cp*Co)₂B₆S₂H₄(CH₂S₂){Fe(CO)₃}] (10). The core structure of 10 is similar to that of [C₂B₉H₁₁]^2- with a five-membered pentahapto coordinating face. All of the synthesized metal-rich metallaheteroboranes have been characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy, ESI-MS, and structurally solved by single-crystal X-ray diffraction analysis. Furthermore, theoretical investigations gave insight into the bonding of such higher-nuclearity clusters containing heavier chalcogen atoms.