Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Sep 6;28(18):6462.
doi: 10.3390/molecules28186462.

The Synthesis, Characterization, and Fluxional Behavior of a Hydridorhodatetraborane

Fatou Diaw-Ndiaye  1 , Pablo J Sanz Miguel  1 , Ricardo Rodríguez  1 , Ramón Macías  1
Affiliations

The Synthesis, Characterization, and Fluxional Behavior of a Hydridorhodatetraborane

Fatou Diaw-Ndiaye et al. Molecules. .

Abstract

The octahydridotriborate anion plays a crucial role in the field of polyhedral boron chemistry, facilitating the synthesis of higher boranes and the preparation of diverse transition metal complexes. Among the stable forms of this anion, CsB3H8 (or (n-C4H9)4N)[B3H8] have been identified. These salts serve as valuable precursors for the synthesis of metallaboranes, wherein the triborate anion acts as a ligand coordinating to the metal center. In this study, we have successfully synthesized a novel rhodatetraborane dihydride, [Rh(η2-B3H8)(H)2(PPh3)2] (1), which represents a Rh(III) complex featuring a bidentate chelate ligand fasormed by B3H8-. Extensive characterization of this rhodatetraborane complex has been performed using NMR spectroscopy in solution and X-ray diffraction analysis in the solid state. Notably, the complex exhibits intriguing fluxional behavior, which has been investigated using NMR techniques. Moreover, we have explored the reactivity of complex 1 towards pyridine (py) and dimethylphenylphosphine (PMe2Ph). Our findings highlight the labile nature of this four-vertex rhodatetraborane as it undergoes disassembly upon attack from the corresponding Lewis base, resulting in the formation of borane adducts, LBH3, where L = py, PMe2Ph. Furthermore, in these reactions, we report the characterization of new cationic hydride complexes, such as [Rh(H)2(PPh3)2 (py)]+ (2) and [Rh(H)2(PMe2Ph)4]+. Notably, the latter complex has been characterized as the octahydridotriborate salt [Rh(H)2(PMe2Ph)4][B3H8] (3), which extends the scope of rhodatetraborane derivatives.

Keywords: boranes; fluxionality; metal hydrides; metallaboranes; solid-state structure.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Reaction between the Wilkinson’s catalyst and the octahydridotriborate anion to give [Rh(η2-B3H8)(H)2(PPh3)2] (1).
Figure 1
Figure 1
ORTEP-type of drawing for [Rh(η2-B3H8)(H)2(PPh3)2] (1), showing the cluster numbering system employed, with 50% thermal ellipsoids for non-hydrogen atoms. The phenyl rings (except for the ipso carbon atoms) are omitted to aid clarity. Selected interatomic distances (Å) and angles (°) with esds in parenthesis: Rh2–P1 2.3103(11), Rh2–P2 2.2911(11), Rh2–H 1.58(2) (average value of the two hydride ligands), Rh2–B1 2.428(5), Rh1–B3 2.420(5), B1–B3 1.764(8), B1–B4 1.790(8), B3–B4 1.805(8), P1–Rh2–P2 158.68(4), B1–Rh2–P1 103.27(13), B1–Rh2–P2 95.72(13), B3–Rh2–P1 106.40(13), B3–Rh2–P2 94.10(13), H–Rh2–P1 81.1(18) (average value of the two hydride ligands), B1–Rh2–B3 42.67(18), B3–B1–Rh2 68.4(2), B1–B3–Rh2 68.9(2), B3–B1–B4 61.0(3), B1–B3–B4 60.2(3), B1–B4–B3 58.8(3). The dihedral angle between planes {B1B3B4} and {B1B3Rh2} is 121.91(3).
Figure 2
Figure 2
Packing of individual molecules of 1 that form ribbons along the a axis (above); detail of edge-to-face phenyl interactions between the molecules within the ribbons (below).
Figure 3
Figure 3
Stick representation of the 11B-{1H} NMR spectra of a series of arachno-metallaboranes. The NMR data were measured in different solvents such as toluene-d8, CD2Cl2 and CDCl3.
Figure 4
Figure 4
Plot of δ(11B) versus δ (1H) for directly bound [BH(terminal)] units in the following arachno-metallatetraboranes: [Nb(η2-B3H8)(η5-C5H5)2], [W(η2-B3H8)(PMe3)3(H)3], [Re(η2-B3H8)(CO)4], [Os(η2-B3H8)(CO)(PPh3)2H], [Ru(η2-B3H8)(CO)(PPh3)2H], [Ir(η2-B3H8)(H)2(PPh3)2] and [Rh(η2-B3H8)(H)2(PPh3)2] (1).
Figure 5
Figure 5
1H-{11B} NMR spectra, in CD2Cl2, at different temperatures, which demonstrate an intramolecular fluxional process for compound 1.
Scheme 2
Scheme 2
A proposed mechanism of intramolecular hydrogen exchange in 1.
Scheme 3
Scheme 3
Reactions of 1 with the ligands py and PMe2Ph.
See this image and copyright information in PMC

References

    1. Barton L., Strivastava D.K. In: Comprehensive Organometallic Chemistry II. Abel E.W., Stone F.G.A., Wilkinson G., editors. Volume 1. Pergamon; New York, NY, USA: 1995. pp. 275–372.
    1. Cotton F.A., Wilkinson G., Murillo C.A., Bochmann M. Advanced Inorganic Chemistry. 6th ed. Wiley; New York, NY, USA: 1999.
    1. Kennedy J.D. Progress in Inorganic Chemistry. Vol. 32. John Wiley & Sons; New York, NY, USA: 1984. The Polyhedral Metalloboranes. 1. Metalloborane Clusters with 7 Vertices And Fewer; pp. 519–679.
    1. Weller A.S. d- and f-Block Metallaboranes. In: Crabtree R.H., Mingos D.M.P., editors. Comprehensive Organometallic Chemistry III. Volume 3. Elsevier; Oxford, UK: 2007. pp. 133–174.
    1. Bould J., Greenwood N.N., Kennedy J.D. The first osmaboranes and a new iridatetraborane. J. Organomet. Chem. 1983;249:11–21. doi: 10.1016/S0022-328X(00)98795-3. - DOI