Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes

The reaction of CoX<inf>2</inf> (X = Cl, Br, NO<inf>3</inf>) with KTp <sup>Ph2</sup> in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp<sup>Ph2</sup>CoX] (X = Cl 1, Br 2, NO<inf>3</inf>3). The reaction of [Tp<sup>Ph2</...

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Main Authors: David J. Harding, Phimphaka Harding, Rathawat Daengngern, Saranphong Yimklan, Harry Adams
Format: Journal
Published: 2018
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http://cmuir.cmu.ac.th/jspui/handle/6653943832/48993
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spelling th-cmuir.6653943832-489932018-08-16T02:08:07Z Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes David J. Harding Phimphaka Harding Rathawat Daengngern Saranphong Yimklan Harry Adams Chemistry The reaction of CoX<inf>2</inf> (X = Cl, Br, NO<inf>3</inf>) with KTp <sup>Ph2</sup> in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp<sup>Ph2</sup>CoX] (X = Cl 1, Br 2, NO<inf>3</inf>3). The reaction of [Tp<sup>Ph2</sup>CoBr] with NaX (X = N<inf>3</inf>, NO<inf>2</inf>) or potassium thiocyanate (KNCS) permits isolation of [Tp<sup>Ph2</sup>CoX] (X = N <inf>3</inf>4, NCS 5, NO<inf>2</inf>6). In contrast, the reaction of cobalt(ii) acetate with KTp<sup>Ph2</sup> yields [Tp<sup>Ph2</sup>Co(OAc)(Hpz <sup>Ph2</sup>)] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of β-diketones in the presence of NaOMe produces the β-diketonate complexes, [Tp<sup>Ph2</sup>Co(β-diketonate)] (β-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the Tp<sup>Ph2</sup> ligands are κ<sup>3</sup>-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 7 reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9 and 10 show cobalt centres with square pyramidal coordination geometries and κ<sup>2</sup>- coordinated β-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible one-electron reduction to Co(i). However, the β-diketonate complexes, 8, 10 and 11 undergo irreversible one-electron oxidation. The redox potential and reversibility increases as the steric bulk of the substituent on the β-diketonate ligand increases. © 2009 The Royal Society of Chemistry. 2018-08-16T02:08:07Z 2018-08-16T02:08:07Z 2009-01-01 Journal 14779234 14779226 2-s2.0-59949083037 10.1039/b815001j https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=59949083037&origin=inward http://cmuir.cmu.ac.th/jspui/handle/6653943832/48993
institution Chiang Mai University
building Chiang Mai University Library
country Thailand
collection CMU Intellectual Repository
topic Chemistry
spellingShingle Chemistry
David J. Harding
Phimphaka Harding
Rathawat Daengngern
Saranphong Yimklan
Harry Adams
Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
description The reaction of CoX<inf>2</inf> (X = Cl, Br, NO<inf>3</inf>) with KTp <sup>Ph2</sup> in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp<sup>Ph2</sup>CoX] (X = Cl 1, Br 2, NO<inf>3</inf>3). The reaction of [Tp<sup>Ph2</sup>CoBr] with NaX (X = N<inf>3</inf>, NO<inf>2</inf>) or potassium thiocyanate (KNCS) permits isolation of [Tp<sup>Ph2</sup>CoX] (X = N <inf>3</inf>4, NCS 5, NO<inf>2</inf>6). In contrast, the reaction of cobalt(ii) acetate with KTp<sup>Ph2</sup> yields [Tp<sup>Ph2</sup>Co(OAc)(Hpz <sup>Ph2</sup>)] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of β-diketones in the presence of NaOMe produces the β-diketonate complexes, [Tp<sup>Ph2</sup>Co(β-diketonate)] (β-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the Tp<sup>Ph2</sup> ligands are κ<sup>3</sup>-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 7 reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9 and 10 show cobalt centres with square pyramidal coordination geometries and κ<sup>2</sup>- coordinated β-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible one-electron reduction to Co(i). However, the β-diketonate complexes, 8, 10 and 11 undergo irreversible one-electron oxidation. The redox potential and reversibility increases as the steric bulk of the substituent on the β-diketonate ligand increases. © 2009 The Royal Society of Chemistry.
format Journal
author David J. Harding
Phimphaka Harding
Rathawat Daengngern
Saranphong Yimklan
Harry Adams
author_facet David J. Harding
Phimphaka Harding
Rathawat Daengngern
Saranphong Yimklan
Harry Adams
author_sort David J. Harding
title Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
title_short Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
title_full Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
title_fullStr Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
title_full_unstemmed Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
title_sort synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
publishDate 2018
url https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=59949083037&origin=inward
http://cmuir.cmu.ac.th/jspui/handle/6653943832/48993
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