Synthesis and Characterization of [exo‐BH₂(Cp*M)₂B₉H₁₄] (M=Ru, Re), and the Conversion of the Ruthenaborane into [(Cp*Ru)₂B₁₀H₁₆] with an Open Cluster Framework Based on a Capped Truncated Tetrahedron

Abstract

The evolution of main-group and transition-metal cluster structural chemistry since the development of the electroncounting rules in the 1970s is an important achievement of modern inorganic chemistry. [1,2] The useful connection between cluster geometry and electronic structure defined by the electron counting rules provides a solid foundation for the rational approach to larger clusters and nanoparticle systems that lie between small clusters and bulk crystalline materials with extended structures. [3] Given the firm connection between the cluster-electron count and the cluster geometry for subicosahedral maingroup clusters, it could be assumed that the structures of clusters based on supraicosahedral frameworks will provide similar unambiguous information. Not so. For example, 14 skeletal electron pair (sep), 12-fragment heteroatomic clusters with carbon or carbon plus a transition metal exhibit at least five different open cluster shapes depending on heteroatom content. [4][5][6] Even the structure of the 13-vertex closed carborane cluster, 1,2-m-C 6 H 4 (CH 2 ) 2 -3-Ph-1,2-C 2 B 11 H 10 , is a variant of the docosahedral structure found by calculations most stable for the 13-vertex homonuclear borane (Scheme 1). [7] In this case, the additional stabilization achieved by generating vertices of connectivity four for the carbon centers more than compensates for that lost in converting a diamond into a rhombus arrangement. Thus for supraicosahedral clusters, the energy differences between possible geometries are much smaller than for subicosahedral clusters and the stabilization achieved by accommodating the properties of hetero atoms determines the observed cluster shape.Herein novel boron-rich metallaboranes with geometries based on supraicosahedral frameworks provide a carbon-free comparison and demonstrate further structural types. These observations do not define the basic supraicosahedral framework structures for homonuclear boranes even though more of the structures accessible can be mapped out empirically. In addition, provided barriers for interconversion are large relative to room-temperature, intermediates in the clusterbuilding process are also likely to be isolated. As shown below, this characteristic of supraicosahedral cluster frameworks has allowed us to isolate and characterize a metallaborane with an unusual structure and to demonstrate that it is an intermediate in the boron cluster framework expansion reaction.In terms of systematic cluster expansion, the most versatile metal is rhenium where known Re 2 B n frameworks run from n = 4 to 10.[8] Ruthenium offers fewer compounds [9,10] but revisiting both systems utilizing large BH 3 excess and forcing conditions permits the isolation of three different compounds with the molecular formula [Cp* 2 M 2 B 10 H 16 ], M = Ru or Re, Cp* = C 5 Me 5 . With formal electron counts of 14 and 13 sep they offer an interesting case study for electron counting/supraicosahedral cluster relationships.The structure of [Cp* 2 Ru 2 B 10 H 16 ] (1) is shown in Figure...

Synthesis and Structural Characterization of New Divanada‐ and Diniobaboranes Containing Chalcogen Atoms

“…Synthesis and characterization of oxavanadaborane 6 and vanadaborane 7 : Recently, we reported the synthesis of divanadaborane from the thermolysis of [Cp 2 VCl 2 ] with LiBH 4 ⋅ THF and a monoborane reagent 10. Interestingly, this result, as well as the existence of higher‐nuclearity rhenaboranes25 and ruthenaboranes,26 led us to revisit the vanadium system that yielded compounds 6 and 7 (Scheme ). The molecular structure of compound 6 (Figure 4) clearly shows that one ethoxy group is bound to two V metal atoms and one B atom.…”

“…Recently, we reported the synthesis of divanadaborane from the thermolysis of [Cp 2 VCl 2 ] with LiBH 4 ·THF and a monoborane reagent. [10] Interestingly, this result, as well as the existence of higher-nuclearity rhenaboranes [25] and ruthenaboranes, [26] led us to revisit the vanadium system that yielded compounds 6 and 7 (Scheme 3). The molecular structure of compound 6 ( Figure 4) clearly shows (5), Nb1-B2 2.470(5), Nb1-B3 2.486(5), Nb1-B4 2.423(3), Nb1-S1 2.4390 (14), B1-B4 1.775 (7), B2-B3 1.701(8), B1-S1 1.809(6); Nb1-S1-Nb2 70.12(4), S1-B1-B4 124.2(3), Nb1-B1-Nb2 69.56 (14).…”

Borane Mimics of Classic Organometallic Compounds: [(Cp*Ru)B8H14(RuCp*)]0,+, Isoelectronic Analogues of Dinuclear Pentalene Complexes

“…Recently we have shown that the reaction of [(Cp*Ru) 2 B 3 H 9 ] with BH 3 ⋅THF leads to metallaboranes containing six, eight, and ten boron atoms 13. 14 The ten boron atom cluster has two colorless isomeric forms, one with an exo‐cluster borane atom on a Ru 2 B 9 cluster framework. This species was shown to be an intermediate on the path to the second isomer which has a Ru 2 B 10 cluster framework.…”

“…This approach has led to the isolation of [(1‐Cp*Ru)B 5 H 10 ] ( 1 ; in which the Cp*Ru fragment occupies the 1‐position of the BH cage) and [(Cp*Ru)B 8 H 14 (RuCp*)] ( 2 ). Metallabarane 2 converts into the isomer pair [(Cp*Ru) 2 B 10 H 16 ]14 on heating in the presence of BH 3 ⋅THF showing that it is indeed another intermediate in the cluster‐building process.…”

Calcium Phosphate‐Reinforced Photosensitizer‐Loaded Polymer Nanoparticles for Photodynamic Therapy

“…With regard to systematic cluster expansion, the most versatile metal is rhenium, and known Re 2 B n frameworks with n =4–10 23a. Fewer compounds are known with ruthenium23b and rhodium,25 but use of a large excess of BH 3 ⋅THF and harsh conditions enables the isolation of 16‐vertex rhodaborane 1 as a moderately stable yellow crystalline solid. The identity of 1 was confirmed by multinuclear NMR spectroscopy, elemental analysis, infrared spectroscopy, and X‐ray structural analysis (Figure 2).…”