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.
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 unparied electron.[1][3][4]
Cobalt(III) and cobalt(V) derivativesedit
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]
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]
^ abcdB. 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.
^ abHolleman, Arnold F.; Wiberg, E.; Wiberg, N. (2007). Lehrbuch der anorganischen Chemie (102nd ed.). Berlin. p. 1695. ISBN978-3-11-017770-1. OCLC 180963521.{{cite book}}: CS1 maint: location missing publisher (link)
^ abE. 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.
^ abcdefE. 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.
^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. ISBN978-3-11-020685-2.
^ abcdE. 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 linksedit
Bower, Barton K. (12 December 1972). "Tetra(bicycloheptyl) transition metal compounds".
February 15, 2024
tetrakis, norbornyl, cobalt, sensitive, organometallic, compound, cobalt, first, synthesized, barton, bower, howard, tennent, 1972, compounds, which, cobalt, formal, oxidation, state, namesother, names, tetrakis, bicyclo, hept, cobaltidentifierscas, number, 36. 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 Tetrakis 1 norbornyl cobalt IV NamesOther names T 4 Tetrakis bicyclo 2 2 1 hept 1 yl cobaltIdentifiersCAS Number 36333 80 9 Y3D model JSmol Interactive imageInChI InChI 1S 4C7H11 Co c4 1 2 7 4 3 6 1 5 7 h4 6H 1 5H2 Key FULAMMPKLQBENQ UHFFFAOYSA NSMILES C1CC2CCC1 C2 Co C CC1 2CCC1C2 C CC1 2CCC1C2 C CC1 2CCC1C2PropertiesChemical formula C 28H 44CoMolar mass 439 593 g mol 1Appearance brown crystalsMelting point 100 C decomposes Solubility soluble in THFExcept where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa Infobox references Contents 1 Preparation 2 Properties 2 1 Stability 2 2 Cobalt III and cobalt V derivatives 3 See also 4 References 5 External linksPreparation editTetrakis 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 2 CoCl 2 THF 4 norLi pentane Co nor 4 Co 4 LiCl 2 THF displaystyle ce 2CoCl2 THF 4norLi gt text pentane Co nor 4 Co 4 LiCl 2THF nbsp nbsp The compound can then be purified by recrystallization Properties editThe complex is a thermally stable homoleptic tetraorganylcobalt IV complex with exclusively s bonding ligands It was the first low spin complex with tetrahedral geometry to be isolated 2 3 4 Stability edit The exceptional stability of the complex is in large part due to its inability to undergo either a or b hydride elimination The a position of the metal corresponding to the 1 position of the norbornyl ligand has no more hydrogen atoms while hydride elimination from the b 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 s 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 unparied electron 1 3 4 Cobalt III and cobalt V derivatives edit 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 3 CoCl 2 THF 8 norLi 5 THF Et 2 O THF 2 Li THF 4 Co nor 4 Co LiCl displaystyle ce 3 CoCl2 THF 8 norLi 5 THF gt atop ce Et2O THF 2 Li THF 4 Co nor 4 Co LiCl nbsp 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 AgThis 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 editMetal tetranorbornylReferences edit a b c d 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 a b 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 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link a b 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 a b c d e f 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 Riedel Erwin Alsfasser R Janiak C Klapotke 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 a b c d 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 editBower Barton K 12 December 1972 Tetra bicycloheptyl transition metal compounds Retrieved from https en wikipedia org w index php title Tetrakis 1 norbornyl cobalt IV amp oldid 1174728343, wikipedia, wiki, book, books, library,
