Homometallic Cubane Clusters: Participation of Three-Coordinated Hydrogen in 60-Valence Electron Cubane Core

This work describes the synthesis, structural characterizations, and electronic structures of a series of novel homometallic cubane clusters [(Cp*Ru)2{Ru(CO)2}2BH(μ3-E)(μ-H)B(μ-H)3M], (2, M = Cp*Ru, E = CO; 3, M = Ru(Cp*Ru)2(μ-CO)3(μ-H)BH), E = BH), [(Cp*Ru)3(μ3-CO)(BH)3(μ3-H)3], 4, and [(Cp*Ru)2(μ3-CO){Ru(CO)3}2(BH)2(μ-H)B], 5 (Cp* = η(5)-C5Me5). These cubane clusters have been isolated from a thermally driven reaction of diruthenium analogue of pentaborane(9) [(Cp*RuH)2B3H7], 1, and [Ru3(CO)12]. Structural and spectroscopic studies revealed the existence of triply bridged hydrogen (μ3-H) atoms that participate as a vertex in the cubane core formation for compounds 2, 3, and 4. In addition, the crystal structure of these clusters clearly confirms the presence of an electron precise borane ligand (borylene fragment) which is triply bridged to the trimetallic units. Bonding of these novel complexes has been studied computationally by DFT methods, and the studies demonstrate that the cubane clusters 2 and 3 possess 60 cluster valence electrons (cves) with six metal-metal bonds. All the new compounds have been characterized in solution by mass spectrometry; IR; and (1)H, (11)B, and (13)C NMR studies, and the structural types were unequivocally established by crystallographic analysis of compounds 2-5.