Tetrakis (1-norbornyl) cobalt (IV)

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Structural formula
Structure of tetrakis (1-norbornyl) cobalt (IV)
General
Surname Tetrakis (1-norbornyl) cobalt (IV)
other names

( T -4) -Tetrakis (bicyclo [2.2.1] hept-1-yl) cobalt

Molecular formula T4 - [Co (nor) 4 ], C 28 H 44 Co
Brief description

brown crystals

External identifiers / databases
CAS number 36333-80-9
Wikidata Q2406745
properties
Molar mass 439.58 g mol −1
Physical state

firmly

Melting point

100 ° C (decomposition)

solubility

soluble in THF

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Tetrakis (1-norbornyl) cobalt (IV) is an air-sensitive, organometallic compound of cobalt . It was first presented by Barton K. Bower and Howard G. Tennent in 1972 and is one of the rare compounds in which cobalt is assigned the formal oxidation state + IV.

presentation

Tetrakis (1-norbornyl) cobalt (IV) can be obtained by the disproportionation reaction of CoCl 2 • THF with 1-norbornyllithium (norLi) in n- pentane under protective gas . The cobalt (II) chloride-THF adduct is by Soxhlet extraction of anhydrous CoCl 2 with THF and the organolithium compound by reaction of 1-chloro norbornane with metallic lithium accessible.

The purification takes place via filtration and recrystallization .

The 1-norbornyl group (nor, or 1-nor)

properties

In this cobalt complex is the first thermally stable homoleptic cobalt (IV) tetra organyl , with only σ -binding ligands . It is also the first isolated low-spin complex with a tetrahedral structure.

stability

The special stability is largely due to the fact that neither α - another β -hydride elimination to take place. In the α- position to the metal (corresponds to the 1-position of the norbornyl ligand) no further hydrogen is bonded and a hydride elimination in the β- position would lead to an energetically unfavorable double bond at the bridgehead atom ( Bredt's rule ). In addition, the bulky norbornyl ligands cause steric shielding of the central atom and prevent rapid ligand substitution and homolysis , with dimerization of the ligands.

The rare d 5 low-spin configuration in the tetrahedral ligand field is achieved in that the ligand, as a very strong σ - or more precisely n - electron pair donor , increases the splitting of the e and t 2 orbital sets in such a way that the spin pairing energy can be overcome. The result is an e 4 t 2 1 configuration and consequently a magnet measurement shows paramagnetism in the order of magnitude of an unpaired electron.

Cobalt (III) and Cobalt (V) analogues

Starting from CoCl 2 • THF and 1-norbornyllithium (norLi), a trivalent cobalt complex can be prepared. If a mixture of diethyl ether and THF is used as a solvent instead of n- pentane , disproportionation occurs with the formation of a tetrakis (1-norbornyl) cobaltate (III) complex, which crystallizes with solvated lithium counterion and elemental cobalt .

The compound is sensitive to air, is green in color, and is paramagnetic, to the extent of two unpaired electrons. As a result, there is also a low-spin configuration with a tetrahedral structure (d 6 , e 4 t 2 2 ).

If tetrakis (1-norbornyl) cobalt (IV) is oxidized with Ag [BF 4 ] in THF , a pentavalent cobalt complex is obtained, which crystallizes with a tetrafluoroborate anion as a counterion.

This complex is the first to be isolated in which cobalt is in the + V oxidation state. This is also a low-spin complex (d 4 , e 4 t 2 0 ).

Individual evidence

  1. a b c d e f B. K. Bower and HG Tennent: Transition metal bicyclo [2.2.1] hept-1-yls . In: J. Am. Chem. Soc. . 94, No. 7, 1972, pp. 2512-2514. doi : 10.1021 / ja00762a056 .
  2. a b c d e f g E. K. Byrne, KH Theopold: Synthesis, characterization, and electron-transfer reactivity of norbornyl complexes of cobalt in unusually high oxidation states . In: J. Am. Chem. Soc. . 111, No. 11, 1989, pp. 3887-3896. doi : 10.1021 / ja00193a021 .
  3. This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  4. ^ A b A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1695.
  5. a b E. K. Byrne, DS Richeson and KH Theopold: Tetrakis (1-norbornyl) cobalt, a low spin tetrahedral complex of a first row transition metal . In: J. Chem. Soc., Chem. Commun. . No. 19, 1986, pp. 1491-1492. doi : 10.1039 / C39860001491 .
  6. C. Janiak, T. Klapötke , H.-J. Meyer, R. Alsfasser, E. Riedel (Ed.): Moderne Anorganische Chemie , 3rd edition, De Gruyter, 2007, ISBN 978-3-11-020685-2 , p. 718.
  7. a b c d E. K. Byrne, KH Theopold: Redox chemistry of tetrakis (1-norbornyl) cobalt. Synthesis and characterization of a cobalt (V) alkyl and self-exchange rate of a Co (III) / Co (IV) couple . In: J. Am. Chem. Soc. . 109, No. 4, 1987, pp. 1282-1283. doi : 10.1021 / ja00238a066 .