Dicarbollide Explained

In organometallic chemistry, a dicarbollide is an anion of the formula [C₂B₉H₁₁]^2-. Various isomers exist, but most common is 1,2-dicarbollide derived from ortho-carborane.^[1] These dianions function as ligands, related to the cyclopentadienyl anion. Substituted dicarbollides are also known such as [C₂B₉H₁₀(pyridine)]⁻ (pyridine bonded to B) and [C₂R₂B₉H₉]^2- (R groups bonded to carbon).

Synthesis of dicarbollides

Dicarbollides are obtained by base-degradation of 12-vertex dicarboranes. This degradation of the ortho derivative has been most heavily studied. The conversion is conducted in two-steps, first "deboronation" and second deprotonation:^[2]

Notes and References

1. Sivaev, I. B. . Bregadze, V. I. . Chemistry of Nickel and Iron Bis(dicarbollides). A Review. Journal of Organometallic Chemistry. 2000. 614-615. 27–36. 10.1016/S0022-328X(00)00610-0.
2. 10.1039/B108937D . Crystal and Molecular Structures of the nido-Carborane Anions, 7,9- and 2,9-C₂B₉H₁₂⁻ . 2002 . Fox . Mark A. . Goeta . Andrés E. . Hughes . Andrew K. . Johnson . Andrew L. . Journal of the Chemical Society, Dalton Transactions . 10 . 2132 .
3. Revisiting [Mn(CO)₃(η⁵-nido-7,8-C₂B₉H₁₁)]⁻, the Dicarbollide Analogue of [(η⁵-C₅H₅)Mn(CO)₃]: Reactivity Studies Leading to Boron Atom Functionalization. Mitsuhiro Hata . Jason A. Kautz . Xiu Lian Lu . Thomas D. McGrath . F. Gordon A. Stone . Organometallics. 2004. 23. 3590–3602. 10.1021/om049822l.
4. Grimes, R. N., Carboranes 3rd Ed., Elsevier, Amsterdam and New York (2016), .
5. Crowther, D. J. . Baenziger, N. C. . Jordan, R. F. . Group 4 metal dicarbollide chemistry. Synthesis, structures and reactivity of electrophilic alkyl complexes (Cp*)(C₂B₉H₁₁)M(R), M = Hf, Zr . Journal of the American Chemical Society . 1991 . 113 . 4 . 1455–1457 . 10.1021/ja00004a080 .
6. Book: Plešek, J. . Heřmánek, S. . Štíbr, B. . Potassium dodecahydro-7,8-dicarba-nido-undecaborate(1-), k[7,8-C₂B₉H₁₂], intermediates, stock solution, and anhydrous salt |chapter=Potassium dodecahydro-7, 8-dicarba-nido -undecaborate(1-), k[7, 8-c2 b9 h12 ], intermediates, stock solution, and anhydrous salt | series = Inorganic Syntheses | year = 1983 | volume = 22 | pages = 231–234 | doi = 10.1002/9780470132531.ch53 |isbn=978-0-470-13253-1 }}

   C₂B₁₀H₁₂ + NaOEt + 2 EtOH → Na⁺C₂B₉H₁₂⁻ + H₂ + B(OEt)₃

   Na⁺C₂B₉H₁₂⁻ + NaH → Na₂C₂B₉H₁₁ + H₂

   The dianion derived from dicarboranes, [C₂B₉H₁₁]^2-, are nido clusters. Three isomers exist. Most commonly studies is the 7,8-isomer, with two adjacent carbon centers on the rim. 7,9- has non-adjacent carbon centers on the rim. It is derived by degradation of meta-. 2,9- has only one carbon center on the rim. It is derived by degradation of para-.^[2]

   Coordination compounds

   A variety of complexes - a subset of metallaborane - are known with one or two dicarbollide ligands. An example of a 1:1 complex is [Mn(CO)₃(η⁵-7,8-C₂B₉H₁₁)]⁻.^[3]

   Most heavily studied are complexes with two dicarbollide ligands, especially sandwich complexes. Thus, these are prepared by salt metathesis reactions, as illustrated by the synthesis of the ferrocene analogue:

   2 Na₂C₂B₈H₁₁ + FeCl₂ → Na₂[Fe(C₂B₈H₁₁)₂] + 2 NaCl

   These bisdicarbollide dianions are often readily oxidized. Fe(III), Co(III), Ni(III), and Ni(IV) derivatives are known. In some cases, the oxidation induces rearrangement of the C₂B₉ cage to give complexes where the carbon centers are nonadjacent.

   Precursor to other carboranes

   Diprotonation of [C₂B₉H₁₁]²⁻ gives the neutral carborane C₂B₉H₁₃. Pyrolysis of this nido cluster gives closo-C₂B₉H₁₁. Chromate-oxidation of [C₂B₉H₁₂]⁻ results in deboronation, giving the C₂B₇H₁₃. This carborane features two CH₂ vertices.^[4]

   Homogeneous catalysis

   The clam-shell dicarbollide complex (Cp*)(C₂B₉H₁₁)ZrCH₃ catalyzes alkene polymerization.^[5]

   References

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