Metal-Rich Fused Clusters: Syntheses, Structures, and Bonding of Heteronuclear Condensed Metallaboranes

Syntheses and structural elucidations of a series of condensed clusters are described. The condensation of nido-[(Cp*Ru)(2)(B3H9)], nido-1, with heavier group 7 metal carbonyl, [Re-2(CO)(10)], yielded [(Cp*Ru)(2)(CO)B3H8{Re(CO)(3)}], 2. Ruthenaborane 2 is an edge-fused cluster of square pyramid {RuReB3} and triangle {RuB2} through a B-B bond. Further, the reaction of arachno-[(Cp*Ru)(2)(B3H8)(CS2H)], arachno-3, with [Co-2(CO)(8)] led to the formation of condensed ruthenaboranes [(Cp*Ru)(2)B3H3S{Co-3(CO)(8)}(SCH3)], 4, and [(Cp*Ru)(2)B3H4{Co-2(CO)(7)}(SCH3)], 5. Cluster 4 comprises two tetrahedron {Co2RuB}, {Co2BS} and pentagonal pyramidal {Co2RuB3} cores, and cluster 5 consists of a butterfly {Ru2B2}, a triangle {CoB2}, and a tetrahedron {Co2B2}. Both clusters 4 and 5 do not follow Mingos' fusion formalism for fused clusters and are unusual examples based on their composition. On the other hand, cluster 2 follows Mingos' fusion formalism. All of the clusters have been characterized by H-1, B-11{H-1}, C-13{H-1} NMR spectroscopies, electrospray ionization (ESI) mass spectrometry, and infrared (IR) spectroscopy, and the solid-state structures were established by single-crystal X-ray diffraction analysis.