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The reaction of the [(η5-C5Me5)MoCl4] complex with [LiBH4·THF] in toluene at -70 °C, followed by pyrolysis at 110 °C, afforded dark brown [(η5-C5Me5Mo)3MoB9H18], 2, in arallel with Ihe known [(η5-C5Me5Mo)2B5H9], 1. Compound 2 has been charactedzed in solution by ¹H, 11B, and 13C NMR spectroscopy and elemental analysis, and the structural types were unequivocally eslablished by crystallographic studies. The title compound represents a novel class of vertex-fused clusters in which a Mo atom has been fused in a perpendicular fashion between two molybdaborane clusters. Electronic structure calculations employing density functional theory yield geometdes in agreement with the structure determinations, and on grounds of density functional theory calculations, we have analyzed the bonding patterns in the structure. [ABSTRACT FROM AUTHOR]

Pyrolysis of (η5-C5Me5WH3)B4H8, 1, in the presence of excess BHCl2·SMe2 in toluene at 100 °C led to the isolation of (η5-C5Me5W)2B5H9, 2, and B−Cl inserted (η5-C5Me5W)2B5H8Cl, 3, and (η5-C5Me5W)2B5H7Cl2, 4−7 (four isomers). All the chlorinated tungstaboranes were isolated as red and air and moisture sensitive solids. These new compounds have been characterized in solution by 1H, 11B, 13C NMR, and the structural types were unequivocally established by crystallographic analysis of compounds 3, 4, and 7. Density functional theory (DFT) calculations were carried out on the model molecules of 3−7 to elucidate the actual electronic structures of these chlorinated species. On grounds of DFT calculations we demonstrated the role of transition metals, bridging hydrogens, and the effect of electrophilic substitution of hydrogens at B−H vertices of metallaborane structures. Reaction of (η5-C5Me5ReH2)2B4H4 with BHCl2·SMe2 led to the isolation of (η5-C5Me5ReH)2B5Cl5, while (η5-C5Me5WH3)B4H8 and an in situ generated intermediate, generated from (η5-C5Me5Mo)Cl4, and LiBH4, offer only partial chlorination at B−H vertices in (η5-C5Me5M)2B5H9 (M = W, Mo). DFT calculations were carried out on the model molecules of these chlorinated species; we demonstrated the role of transition metals, bridging hydrogens, and the effect of electrophilic substitution of hydrogens at B−H vertices of (η5-C5Me5M)2B5H9 (M = W, Mo). [ABSTRACT FROM AUTHOR]

The reaction of [Cp*MoCl4] with an excess of LiBH4, followed by thermolysis with tellurium powder in toluene, afforded a tricapped cubane cluster, [(Cp*Mo)4B4H4(μ4-BH)3] (1), which represents an unprecedented metal-rich metallaborane cluster with a cubane core containing 58 cluster valence electrons (cve) and three metal-metal bonds. [ABSTRACT FROM AUTHOR]

The reaction of [Cp*TaCl4], 1 (Cp* = η5-C5Me5), with [LiBH4·THF] at -78 °C, followed by thermolysis in the presence of excess [BH3·THF], results in the formation of the oxatantalaborane cluster [(Cp*Ta)2B4H10O], 2 in moderate yield. Compound 2 is a notable example of an oxatantalaborane cluster where oxygen is contiguously bound to both the metal and boron. Upon availability of 2, a room temperature reaction was performed with [Fe2(CO)9], which led to the isolation of [(Cp*Ta)2B2H4O{H2Fe2(CO)6BH}], 3. Compound 3 is an unusual heterometallic boride cluster in which the [Ta2Fe2] atoms define a butterfly framework with one boron atom lying in a semi-interstitial position. Likewise, the diselenamolybdaborane, [(Cp*Mo)2B4H4Se2], 4 was treated with an excess of [Fe2(CO)9] to afford the heterometallic boride cluster [(Cp*MoSe)2Fe6(CO)13B2(BH)2], 5. The cluster core of 5 consists of a cubane [Mo2Se2Fe2B2] and a tricapped trigonal prism [Fe6B3] fused together with four atoms held in common between the two subclusters. In the tricapped trigonal prism subunit, one of the boron atoms is completely encapsulated and bonded to six iron and two boron atoms. Compounds 2, 3, and 5 have been characterized by mass spectrometry, IR, 1H, 11B, 13C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Furthermore, the calculated 11B NMR chemical shifts also support the structural characterization of the compounds. Natural bond order analysis and Wiberg bond indices are used to gain insight into the bonding patterns of the observed geometries of 2, 3, and 5. [ABSTRACT FROM AUTHOR]

The reinvestigation of an early synthesis of heterometallic cubane-type clusters has led to the isolation of a number of new clusters which have been characterized by spectroscopic and crystallographic techniques. The thermolysis of [(Cp*Mo)2B4H4E2] (1: E = S; 2: E = Se; Cp* = η5-C5Me5) in presence of [Fe2(CO)9] yielded cubane-type clusters [(Cp*Mo)2(μ3-E)2B2H(μ-H){Fe(CO)2}2Fe(CO)3], 4 and 5 (4: E = S; 5: E = Se) together with fused clusters [(Cp*Mo)2B4H4E2Fe(CO)2Fe(CO)3] (8: E = S; 9: E = Se). In a similar fashion, reaction of [(Cp*RuCO)2B2H6], 3, with [Fe2(CO)9] yielded [(Cp*Ru)2(μ3-CO)2B2H(μ-H){Fe(CO)2}2Fe(CO)3], 6, and an incomplete cubane cluster [(μ3-BH)3(Cp*Ru)2{Fe(CO)3}2], 7. Clusters 4-6 can be described as heterometallic cubane clusters containing a Fe(CO)3 moiety exo-bonded to the cubane, while 7 has an incomplete cubane [Ru2Fe2B3] core. The geometry of both compounds 8 and 9 consist of a bicapped octahedron [Mo2Fe2B3E] and a trigonal bipyramidal [Mo2B2E] core, fused through a common three vertex [Mo2B] triangular face. In addition, thermolysis of 3 with [Mn2(CO)10] permits the isolation of arachno-[(Cp*RuCO)2B3H7], 10. Cluster 10 constitutes a diruthenaborane analogue of 8-sep pentaborane(11) and has a structural isomeric relationship to 1,2-[{Cp*Ru}2(CO)2B3H7]. [ABSTRACT FROM AUTHOR]