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, [Re2(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 [Co2(CO)8] led to the formation of condensed ruthenaboranes [(Cp*Ru)2B3H3S{Co3(CO)8}(SCH3)], 4, and [(Cp*Ru)2B3H4{Co2(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 1H, 11B{1H}, 13C{1H} 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.