Cluster Fusion: Face-Fused Macropolyhedral Tetracobaltaboranes

Polyhedral and Macropolyhedral Metal-Rich Cobaltaboranes: A 25-Vertex Hourglass-Shaped Cluster

In an effort to break the single-cage 16-vertex supraicosahedral barrier, we have explored the reaction of [Cp*CoCl2], 1 with [LiBH4·THF], followed by thermolysis with [BH3·SMe2] [Cp* = η5-C5Me5]. Although our objective to synthesize a high-nuclearity single-cage cluster was not achieved, we have isolated a 25-vertex macropolyhedral cluster [(Cp*Co)5Co2B18H17(CH3)S] (2). Cluster 2 is an exceptional fused hourglass-shaped macropolyhedral cluster composing two icosahedral cores ([Co3B9] and [Co4B8]) and three tetrahedral cores [Co2B2]. Although the fusion in cluster 2 is very complex, it follows Mingos fusion formalism, leading to an attractive hourglass-shaped cluster. Through subtle changes in reaction conditions, two new cobaltaborane clusters, nido-4,5,7-[(Cp*Co)3B7H11] (3) and nido-2,9-[(Cp*Co)2B8H12] (4), have been isolated. The observed core geometries of clusters 3 and 4 are similar to the parent deltahedra [B10H14] with (n + 2) SEP (SEP = skeletal electron pair, n = no. of vertices). All the synthesized cobaltaboranes have been characterized in solution by ESI-mass, nuclear magnetic resonance spectroscopy, infrared spectroscopy and structurally solved by single-crystal X-ray diffraction analysis.

Chemistry of CS2 and CS3 Bridged Decaborane Analogues: Regular Coordination Versus Cluster Expansion

In an effort to synthesize metallaheteroborane clusters of higher nuclearity, the reactivity of metallaheteroboranes, nido-[(Cp*M)2B6S2H4(CS3)] (Cp* = C5Me5) (1: M = Co; 2: M = Rh) with various metal carbonyls have been investigated. Photolysis of nido-1 and nido-2 with group 6 metal carbonyls, M'(CO)5.THF (M' = Mo or W) were performed that led to the formation of a series of adducts [(Cp*M)2B6S2H4(CS3){M'(CO)5}] (3: M = Co, M' = Mo; 4: M = Co, M' = W; 5: M = Rh, M' = Mo; 6: M = Rh, M' = W) instead of cluster expansion reactions. In these adducts, the S atom of C=S group of di(thioboralane)thione {B2CS3} moiety is coordinated to M'(CO)5 (M = Mo or W) in η1-fashion. On the other hand, thermolysis of nido-1 with Ru3(CO)12 yielded one fused metallaheteroborane cluster [{Ru(CO)3}3S{Ru(CO)}{Ru(CO)2}Co2B6SH4(CH2S2){Ru(CO)3}2S], 7. This 20-vertex-fused cluster is composed of two tetrahedral {Ru3S} and {Ru2B2}, a flat butterfly {Ru3S} and one octadecahedron {Co2RuB7S} core with one missing vertex, coordinated to {Ru2SCH2S2} through two boron and one ruthenium atom. On the other hand, the room temperature reaction of nido-2 with Co2(CO)8 produced one 19-vertex fused metallaheteroborane cluster [(Cp*Rh)2B6H4S4{Co(CO)}2{Co(CO)2}2(μ-CO)S{Co(CO)3}2], 8. Cluster 8 contains one nido-decaborane {Rh2B6S2}, one butterfly {Co2S2} and one bicapped square pyramidal {Co6S} unit that exhibits an intercluster fusion with two sulfur atoms in common. Clusters 3-6 have been characterized by multinuclear NMR and IR spectroscopy, mass spectrometry and structurally determined by XRD analyses. Furthermore, the DFT calculations have been carried out to gain insight into electronic, structural and bonding patterns of the synthesized clusters.

Cluster Growth Reactions: Structures and Bonding of Metal-Rich Metallaheteroboranes Containing Heavier Chalcogen Elements

In an effort to synthesize cobalt-rich metallaheteroboranes from decaborane(14) analogues, we have studied the reaction of 10-vertex nido-[(Cp*Co)₂B₆H₆E₂] (Cp* = η⁵-C₅Me₅, 1: E = Se and 2: E = Te) with [Co₂(CO)₈] under thermolytic conditions. All of these reactions yielded face-fused clusters, [(Cp*Co)₂B₆H₆E₂{Co(CO)}(μ-CO){Co₃(CO)₆}] (3: E = Se and 4: E = Te). Further, when clusters 3 and 4 were treated with [Co₂(CO)₈], they underwent further cluster buildup reactions leading to the formation of 16-vertex doubly face-fused clusters [(Cp*Co)₂B₆H₆E₂{Co₂(CO)₂}(μ-CO)₂{Co₄(CO)₈}] (5: E = Se and 6: E = Te). Cobaltaheteroboranes 3 and 4 comprise one icosahedron {Co₄B₆E₂} and one square pyramidal {Co₃B₂} moiety, whereas 5 and 6 are made with one icosahedron {Co₄B₆E₂} and two square pyramidal {Co₃B₂} cores. In an attempt to generate heterometallic metal-rich clusters, we have explored the reactivity of decaborane(14) analogue nido-[(Cp*Co)₂B₇TeH₉] (7) with [Ru₃(CO)₁₂] at 80 °C, which afforded face-fused 13-vertex cluster [(Cp*Co)₂B₇H₇Te{Ru₃(CO)₈}] (8). Cluster 8 is a rare example of a metal-rich metallaheteroborane in which one icosahedron {Co₂Ru₂B₇Te} and a tetrahedron {Ru₂B₂} units are fused through a common {RuB₂} triangular face. Further, the treatment of nido-[(Cp*Co)₂B₆S₂H₄(CH₂S₂)] (9) with [Fe₂(CO)₉] afforded 11-vertex nido-[(Cp*Co)₂B₆S₂H₄(CH₂S₂){Fe(CO)₃}] (10). The core structure of 10 is similar to that of [C₂B₉H₁₁]^2- with a five-membered pentahapto coordinating face. All of the synthesized metal-rich metallaheteroboranes have been characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy, ESI-MS, and structurally solved by single-crystal X-ray diffraction analysis. Furthermore, theoretical investigations gave insight into the bonding of such higher-nuclearity clusters containing heavier chalcogen atoms.

Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]2 with [LiBH4·THF] and subsequent photolysis with excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* = η5-C5Me5). The reaction of Li[BH2S3] with the dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded the 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB3} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.