Tetrakis(1-norbornyl)cobalt(IV)

Tetrakis(1-norbornyl)cobalt(IV)

Names
Other names (T-4)-Tetrakis(bicyclo[2.2.1]hept-1-yl)cobalt
Identifiers
CAS Number	36333-80-9  Y
3D model (JSmol)	Interactive image
InChI InChI=1S/4C7H11.Co/c4*1-2-7-4-3-6(1)5-7;/h4*6H,1-5H2; Key: FULAMMPKLQBENQ-UHFFFAOYSA-N
SMILES C1CC2CCC1(C2)[Co](C(CC1)2CCC1C2)(C(CC1)2CCC1C2)C(CC1)2CCC1C2
Properties
Chemical formula	C28H44Co
Molar mass	439.593 g·mol−1
Appearance	brown crystals
Melting point	100 °C (decomposes)
Solubility	soluble in THF
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Tetrakis(1-norbornyl)cobalt(IV) is an air-sensitive organometallic compound of cobalt. It was first synthesized by Barton K. Bower and Howard G. Tennent in 1972 ^[1] and is one of few compounds in which cobalt has a formal oxidation state of +4.

Preparation

Tetrakis(1-norbornyl)cobalt(IV) is formed the reaction of CoCl₂•THF with 1-norbornyllithium (norLi) in n-pentane under an inert atmosphere. ^[1] The cobalt(II) chloride-THF adduct is prepared from Soxhlet extraction of anhydrous CoCl₂ with THF, and the organolithium reagent is prepared from the reaction between 1-chloro-norbornane and lithium metal in a solvent such as pentane:

2 CoCl₂•THF + 4 norLi → [Co(nor)₄] + Co + 4 LiCl + 2 THF

The compound can then be purified by recrystallization.

Properties

The complex is a thermally stable homoleptic tetraorganylcobalt(IV) complex with exclusively σ-bonding ligands. It was the first low-spin complex with tetrahedral geometry to be isolated. ^{[2] [3] [4]}

Stability

The exceptional stability of the complex is in large part due to its inability to undergo either α- or β-hydride elimination. The α-position of the metal (corresponding to the 1-position of the norbornyl ligand) has no more hydrogen atoms, while hydride elimination from the β-position would yield an energetically unfavorable double bond on a bridgehead atom (Bredt's rule). Moreover, the bulky norbornyl ligands sterically shield the central atom, hindering ligand substitutions as well as homolysis. ^{[1] [5]}

The rare d⁵ low-spin configuration in a tetrahedral ligand field is possible because the ligand is so strongly σ-donating that the gap between the e und t₂ orbitals is raised sufficiently to overcome the spin pairing energy. The resulting configuration is e⁴t₂¹, with magnetic measurements showing paramagnetism consistent with only one unpaired electron. ^{[1] [3] [4]}

Cobalt(III) and cobalt(V) derivatives

The reaction between CoCl₂•THF and 1-norbornyllithium (norLi) also allows the formation of a cobalt(III) complex: if a mixture of diethyl ether and THF is used as the solvent in place of n-pentane, the resulting disproportionation reaction affords the complex tetrakis(1-norbornyl)cobaltate(III), which crystallizes out of solution with solvated lithium counterions, along with elemental cobalt. ^{[4] [6]}

${\displaystyle {\ce {3{CoCl2.THF}+8{norLi}+5{THF}->[{} \atop {\ce {Et2O/THF}}]2{[Li(THF)4][Co(nor)4]}+{Co}+LiCl}}}$

The compound is air-sensitive, has a green color and is paramagnetic, with two unpaired electrons, again indicating a low-spin tetrahedral configuration (d⁶, e⁴t₂²). ^{[6] [4]}

The corresponding cobalt(V) complex is prepared by oxidizing tetrakis(1-norbornyl)cobalt(IV) with Ag[BF₄] in THF and crystallizes with tetrafluoroborate as the counterion. ^{[6] [4]}

Co(nor)₄ + AgBF₄ → [Co(nor)₄]BF₄ + Ag

This complex :[Co(nor)₄]⁺ is the first cobalt(V) complex to be isolated. Again the configuration is low-spin (d⁴, e⁴t₂⁰). ^{[2] [4] [6]}

See also

• Metal tetranorbornyl

References

1. B. K. Bower and H. G. Tennent (1972). "Transition metal bicyclo[2.2.1]hept-1-yls". J. Am. Chem. Soc. 94 (7): 2512–2514. doi:10.1021/ja00762a056.
2. Holleman, Arnold F.; Wiberg, E.; Wiberg, N. (2007). Lehrbuch der anorganischen Chemie (102nd ed.). Berlin. p. 1695. ISBN   978-3-11-017770-1. OCLC   180963521.
3. E. K. Byrne, D. S. Richeson and K. H. Theopold (1986). "Tetrakis(1-norbornyl)cobalt, a low spin tetrahedral complex of a first row transition metal". J. Chem. Soc., Chem. Commun. (19): 1491–1492. doi:10.1039/C39860001491.
4. E. K. Byrne, K. H. Theopold (1989). "Synthesis, characterization, and electron-transfer reactivity of norbornyl complexes of cobalt in unusually high oxidation states". J. Am. Chem. Soc. 111 (11): 3887–3896. doi:10.1021/ja00193a021.
5. Riedel, Erwin; Alsfasser, R.; Janiak, C.; Klapötke, T. M.; Meyer, H.-J. (2007). Moderne Anorganische Chemie. Berlin • New York: Walter de Gruyter. p. 718. doi:10.1515/9783110206852. ISBN   978-3-11-020685-2.
6. E. K. Byrne, K. H. Theopold (1987). "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". J. Am. Chem. Soc. 109 (4): 1282–1283. doi:10.1021/ja00238a066.

External links

• Bower, Barton K. (12 December 1972). "Tetra(bicycloheptyl) transition metal compounds".