Synthesis and characterization of the nine-atom, rhena- and tungsta-boranes (Cp*Re)2B7H7 and (Cp*W)2B7H9, Cp* = η5-C5Me5. Molecular mimics of hypoelectronic main-group clusters in Zintl phases

Abstract

Geometric and molecular orbital analyses of the metallaboranes (Cp*Re) 2 B 7 H 7 and (Cp*W) 2 B 7 H 9 , which display unusual, but identical, core structures and skeletal electron pair counts of n 2 2, demonstrate a close connection between these molecular compounds and anionic, hypoelectronic main-group clusters found in the solid state.

Fine-Tuning of Metallaborane Geometries: Chemistry of Iridaboranes Derived from the Reaction of [(Cp*Ir)2HxCl4−x] (x=0-2; Cp*=η5-C5Me5) with LiBH4

“…On the basis of spectroscopic data, the compound is formulated as a 9-sep, six-vertex, arachno-dimetallahexaborane, demonstrating that cluster expansion by the formal insertion of two BH fragments into 3 has taken place. According to the known structure of B 6 H 12 , there are three possible structures for a hexaborane (12) analogue in which two BH vertices are replaced by two Cp*Ir fragments which are consistent with the solution NMR data.…”

“…Compound 5 represents the first example of a metallaborane analogue of hexaborane (12). The structural metrics of 5 are comparable to those of 3.…”

“…Metal identity affects products. For example, earlier transition metals facilitate hydrogen loss, leading to highly condensed clusters, such as [{Cp*Re} 2 B 7 H 7 ], [12] whereas later transition elements form stable nido-metallaboranes, such as 2,4-[{Cp*Co} 2 B 3 H 7 ] [4] and [1,2-{Cp*Ru} 2 B 4 H 10 ]. [6] Thus, we expect Ir also to exhibit characteristics related to, but different from, those of its Group 9 congeners.…”

Synthesis of [(Cp*Re)2BnHn]n=8-10: Metal Boride Particles That Stretch the Cluster Structure Paradigms

“…Comparing 9 sep [(Cp*Rh) 2 (m-h 6 :h 6 -C 4 H 4 B 2 Me 2 )] 2 [28] with 6 sep [{Cp*Re) 2 (m-h 6 :h 6 -B 6 H 6 )] shows that as the Cp*M fragments are moved within bonding distance three orbitals, which are filled in the 9 sep compound, are emptied and a substantial HOMO ± LUMO gap is produced for 6 sep. [29] Likewise, the generation of the observed structure of [(Cp*Re) 2 B 7 H 7 ] from the canonical tricapped trigonal prismatic geometry causes three orbitals to rise sufficiently high in energy to become unoccupied. [15,30] As with the triple-decker complexes, these molecular orbitals consist of an ReRe antibonding orbital and two ReB orbitals that are boron-ring ± metal d antibonding. The ring orbitals emptied are also BB bonding which is consistent with decreased BÀB bonding.…”

Molecular Models of Solid State Metal Boride Structures

“…B H and the isoelectronic and isostructural (Cp*Re) B H prepared by the cluster expansion reaction of (Cp*Re) B H with BH THF (37,38) exhibit an unprecedented cluster core geometry for nine-vertex systems. As shown in Fig.…”