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Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexesCCDC reference numbers CCDC 699940 and 699941. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b815001j.

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Title: Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexesCCDC reference numbers CCDC 699940 and 699941. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b815001j.
Authors: David J. Harding1, Phimphaka Harding1, Rathawat Daengngern1, Saranphong Yimklan2, Harry Adams2
Source: Dalton Transactions: An International Journal of Inorganic Chemistry. Feb2009, Vol. 2009 Issue 8, p1314-1320. 7p.
Subjects: Complex compounds synthesis, Oxidation-reduction reaction, Cobalt compounds, Crystallography, Chemical reactions, Tetrahydrofuran, Thiocyanates
Abstract: The reaction of CoX2(X = Cl, Br, NO3) with KTpPh2in tetrahydrofuran (THF) yields the half-sandwich compounds [TpPh2CoX] (X = Cl 1, Br 2, NO33). The reaction of [TpPh2CoBr] with NaX (X = N3, NO2) or potassium thiocyanate (KNCS) permits isolation of [TpPh2CoX] (X = N34, NCS 5, NO26). In contrast, the reaction of cobalt(ii) acetate with KTpPh2yields [TpPh2Co(OAc)(HpzPh2)] 7as a result of B–N bond cleavage. Subsequent reaction of 7with a range of β-diketones in the presence of NaOMe produces the β-diketonate complexes, [TpPh2Co(β-diketonate)] (β-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the TpPh2ligands are κ3-coordinated and that the β-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in solution. X-Ray crystallographic studies of 7reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9and 10show cobalt centres with square pyramidal coordination geometries and κ2-coordinated β-diketonate ligands. Cyclic voltammetric studies of 6reveal irreversible one-electron reduction to Co(i). However, the β-diketonate complexes, 8, 10and 11undergo irreversible one-electron oxidation.The redox potential and reversibility increases as the steric bulk of the substituent on the β-diketonate ligand increases. [ABSTRACT FROM AUTHOR]
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Abstract:The reaction of CoX2(X = Cl, Br, NO3) with KTpPh2in tetrahydrofuran (THF) yields the half-sandwich compounds [TpPh2CoX] (X = Cl 1, Br 2, NO33). The reaction of [TpPh2CoBr] with NaX (X = N3, NO2) or potassium thiocyanate (KNCS) permits isolation of [TpPh2CoX] (X = N34, NCS 5, NO26). In contrast, the reaction of cobalt(ii) acetate with KTpPh2yields [TpPh2Co(OAc)(HpzPh2)] 7as a result of B–N bond cleavage. Subsequent reaction of 7with a range of β-diketones in the presence of NaOMe produces the β-diketonate complexes, [TpPh2Co(β-diketonate)] (β-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the TpPh2ligands are κ3-coordinated and that the β-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in solution. X-Ray crystallographic studies of 7reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9and 10show cobalt centres with square pyramidal coordination geometries and κ2-coordinated β-diketonate ligands. Cyclic voltammetric studies of 6reveal irreversible one-electron reduction to Co(i). However, the β-diketonate complexes, 8, 10and 11undergo irreversible one-electron oxidation.The redox potential and reversibility increases as the steric bulk of the substituent on the β-diketonate ligand increases. [ABSTRACT FROM AUTHOR]
ISSN:14779226
DOI:10.1039/b815001j