Nové boranové klastry

Trikarbollidové klastry

Kontakt: B. Štíbr

Rozvoj chemie karboranů, jež obsahují v boranovém skeletu  tři klastrové atomy uhlíku. Tyto sloučeniny byly poprvé připraveny v našem ústavu v. 1995. Nyní se soustřeďujeme na vývoj nových, originálních syntetických postupů založených na inkorporaci dalšího atomu uhlíku do klastrové struktury dikarbaboranů. Trikarbaborany jsou úplná strukturní analoga cyklopentadienidového aniontu a mají i analogické chemické chování. Inkorporací fragmentu {CpFe} vznikají nesmírně stabilní karboranová analoga ferrocenu. Potenciál této chemie se skrývá v modifikacích tvaru karboranového klastru a organického substituentu v exoedrické poloze. Využitelnost pro vývoj nové generace  biologicky aktivních sloučenin na bázi boranových klastrů.

Arenové komplexy železa

V poslední době se připojujeme k resuscitaci polozapomenuté chemie arenových komplexů železa, jež zahrnuje reaktivitu kationtových komplexů [(arene)₂Fe]²⁺, [(arene)FeCp]⁺ a [(arene)Fe(chd)]⁺ (chd = cyclohexadienyl). V centru pozornosti jsou hlavně přeměny spojené s výměnou jednoho arenového ligandu za karboranový nebo heteroboranový ligand, jenž je schopen vytvořit pí-donorovou vazbu k centrálnímu atomu Fe. Vedle toho sledujeme i zajímavé reakce vedoucí k nukleofilní adici aniontů schopných sigma-vazby na aromatický ligand v Fe-komplexu. Takovými vlastnostmi se vyznačují karbanionty a karboranové anionty odvozené odtržením protonu z klastrové CH vazby. Jako arenový ligand volíme s oblibou polymethylované deriváty benzenu. Připravené komplexy se např. vyznačují variabilitou redox potenciálů Fe^II/Fe^III, které je možno přesně nastavit obměnou počtu methylových substituentů (n) na arenovém kruhu.

• Holub J., Růžička A., Padělková Z., Štíbr B.: Alternative syntheses and X-ray diffraction analyses of the parent tricarbaborane compounds [nido-7,8,9-C₃B₈H₁₁](-), [nido-7,8,10-C₃B₈H₁₁]^- and [1-eta⁵-(C₅H₅)-closo-1,2,4,10-FeC₃B₈H₁₁], J. Organomet. Chem. 2011, 696, 2742-2745.
• Štíbr B., Bakardjiev M.; Holub J., Růžička A., Padělková Z., Štěpnička P.: Additive Character of Electron Donation by Methyl Substituents within a Complete Series of Polymethylated [1-(eta⁶-Me_nC₆H_6-n)-closo-1,2,3-FeC₂B₉H₁₁] Complexes. Linear Correlations of the NMR Parameters and FeII/III Redox Potentials with the Number of Arene Methyls, Inorg. Chem. 2011, 50, 3097-3102.
• Holub J., Štíbr B., Bakardjiev M., Růžička A., Padělková Z.: Thermal isomerization of eta⁶-arene ferradicarbolllides. Experimental proof for isolobal relation between (eta⁶-arene)Fe and (eta⁵-cyclopentadienyl)Co cluster units, Dalton Trans. 2011, 40, 6623-6625.
• Štíbr B., Bakardjiev M., Hájková Z., Holub J., Růžička A., Padělková Z., Kennedy J. D.:  .Polymethylated [Fe(eta⁶-arene)₂]²⁺ dications: methyl-group rearrangements and application of the EINS mechanism, Dalton Trans. 2011, 40, 5916-5920.
• Štíbr B., Bakardjiev M., Holub J., Růžička A., Padělková Z., Olejník R., Švec P.: Skeletal alkylcarbonation (SAC) reactions as a simple design for cluster-carbon insertion and cross coupling: High-yield access to substituted tricarbollides from 6,9-dicarba-arachno-decaborane(14), Chem. Eur. J. 2011, 17, 13156-13159 . 

Grantová podpora
Projekt Grantové Agentury České Republiky "Arenové komplexy železa modifikované karborany" (P207/11/0705, 2011-2015)

1. The Synthesis of New Large Boron Hydride Clusters and their Properties

Furthermore...

By using the [B₁₉H₂₂]^- anion as an intermediate, we successfully effected the first isomerisation pathway between anti-B₁₈H₂₂ and syn-B₁₈H₂₂!  As the major synthesis of B₁₈H₂₂ results in the formation of both isomers, the isomerisation route we describe could be useful in individual isomer enrichment.

Find out more: An Experimental Solution to the "Missing Hydrogens" Question Surrounding the Macropolyhedral 19-Vertex Boron Hydride Monoanion [B₁₉H₂₂]^-, a Simplification of Its Synthesis, and Its Use as an Intermediate in the First Example of syn-B₁₈H₂₂ to anti-B₁₈H₂₂ Isomer Conversion. Londesborough MGS, Bould J , Base T, Hnyk D, Bakardjiev M, Holub J, Cisarova I, Kennedy JD. Inorg. Chem., 2010, 49, 9, 4092-4098

We are also interested in the photophysical properties of B₁₈H₂₂. The anti-B₁₈H₂₂ isomers shows a beautiful blue fluorescence with a high quantum yield, ΦF = 0.97, which is very rare amongst inorganic compounds and unique amongst the binary boron hydrides. It also produces singlet oxygen O2(1Δg, ΦΔ 0.008), which opens the door to several interesting possible applications. Conversely, isomer syn-B₁₈H₂₂ shows no measurable fluorescence, instead displaying much faster, picosecond nonradiative decay of excited singlet states. Computed potential energy hypersurfaces (PEHs) for both isomers rationalize these observations, pointing to a deep S1 minimum for anti-B₁₈H₂₂ and a conical intersection (CI) between its S0 and S1 states that lies 0.51 eV higher in energy. Such an energy barrier to nonradiative relaxation is not present in the PEH of syn-B₁₈H₂₂, and the system therefore has sufficient initial energy on excitation to reach the (S0/S1) CI and to then decay to the ground state without fluorescence. The computational analysis of the geometries at stationary points along the PEH of both isomers shows that the determining factor for the dissimilar photophysics of anti- and syn-B₁₈H₂₂ is reasonably due to the significant differences in the geometrical rearrangements at their respective conical intersections.

Find out more: The Distinct Photophysics Of the Isomers of B₁₈H₂₂ Explained. M.G.S. Londesborough, D. Hnyk, J. Bould, L. Serrano-Andrés, V. Sauri, J. M. Oliva, P. Kubát, T. Polívka, and K. Lang. Inorg. Chem. 2012. DOI: 10.1021/ic201726k.

2. Metallaboranes and Their Properties

Kontakt: M.G.S. Londesborough

The flexible bonding nature of the boron hydrides allows ligated metal fragments that are isolobal and isoelectronic with vertices to be accompanied into their cluster structures.  The result is the diverse and exotic field of the metallaboranes.  We are interested in exploring the addition of platinum, palladium, rhodium, iridium and cobalt insertions into borane clusters and experimenting with their chemical and physical properties.

Recent Results from the lab...

We recently discovered that the metallaborane system L₄M₂B₁₀H₁₀ (where M = Pt, Pd and L = phosphine or other ligand) can selectively and reversibly uptake various small molecules of gases (SO₂, CO, NOx, acetylene, ethylene, etc.). There are numerous potential ways to tune the properties of this system according to requirement. It is presently undergoing an extensive experimental screening for potential applications such as low-concentration gas sensors.

A dark purple solution of (PMe₂Ph)₄Pt₂B₁₀H₁₀ turns yellow after bubbling SO₂ (right) through and orange after exposure to air (left). The colour change indicates the SO₂ or O₂ gas uptake on the bimetallaborane clusters.

In the M₂B₁₀H₁₀ system there is potential for artificial photosynthetic use with attached photoantennas, for small molecules recognition and delivery, dioxygen, CO or other small molecule activation and detection. Advanced catalytic processes are one of the potential applications of this system. Immobilizations of these molecules on a solid support can be used for heterogeneous performance.

Find out more: Reversible Capture of Small Molecules On Bimetallaborane Clusters: Synthesis and Structural and Photophysical Characterisation. J. Bould, T. Baše, M.G.S. Londesborough, J. D. Kennedy, Luis A.Oro, Ramón Macías, P. Kubát, M. Fuciman, T Polívka and K. Lang, Inorg. Chem., 2011, 50, 7511-7523.