Metal Rich Metallaboranes: Synthesis, Structure and Bonding of pileo-[(Cp*Ru)₂M(CO)₃(µ-H)(µ-E)(µ₃-BH)B₂H₅] (M = Mo, W, E = CO, and M = Mn, E = H) Clusters

The synthesis and structural characterization of a series of heterotrimetallic ruthenaborane clusters are reported. The photolytic reaction of nido-[(Cp*Ru)2(µ-H)2B3H7] (nido-1) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with [M(CO)5·THF] (THF = tetrahydrofuran, M = Mo and W) yielded the heterotrimetallic clusters pileo-[(Cp*Ru)2{M(CO)3}(µ-CO)(µ-H)(µ3-BH)B2H5], M = Mo (2), W (3) and the known arachno ruthenaboranes [1,2-(Cp*Ru)(Cp*RuCO)(µ-H)B3H8] (I) and [{Cp*Ru(CO)}2B2H6] (II). In an attempt to synthesize the Mn-analog of 2 and 3, we performed a similar reaction of nido-1 with [Mn2(CO)10], which afforded the heterotrimetallic pileo-[(Cp*Ru){Mn(CO)3}(µ-H)2(µ3-BH)B2H5] (4) cluster along with the reported trimetallic hydrido(hydroborylene) species [(Cp*Ru)2{Mn(CO)3}(µ-H)(µ-CO)3(µ-BH)] (III). Ruthenaboranes 2, 3 and 4 are isoelectronic and isostructural. The geometry of 2–4 can be viewed as a triangle face-fused square pyramidal and tetrahedral geometry, in which the apical vertex of the tetrahedron is occupied by a µ3–BH moiety. All of these pileo ruthenaborane clusters obey Mingos’ fusion formalism. Clusters 2–4 were characterized using multinuclear NMR, IR spectroscopies and electrospray ionization mass spectrometry. The single-crystal X-ray diffraction studies of clusters 2 and 4 confirmed their structures. Further, density functional theory (DFT) studies of these pileo ruthenaboranes have been carried out to investigate the nature of bonding, fusion and electronic structures.