Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand
Chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, caH<sub>2</sub>) as a bidentate ligand for Nb(V) as a metal center is presented. The different coordination behavior of caH<sub>2</sub> is well illustrated by a monomeric (Et<sub>4</sub>N)<i>cis&...
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MDPI AG
2022-10-01
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| Series: | Inorganics |
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| Online Access: | https://www.mdpi.com/2304-6740/10/10/166 |
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| author | Alebel Nibret Belay Johan Andries Venter Orbett Teboho Alexander Andreas Roodt |
| author_facet | Alebel Nibret Belay Johan Andries Venter Orbett Teboho Alexander Andreas Roodt |
| author_sort | Alebel Nibret Belay |
| collection | DOAJ |
| description | Chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, caH<sub>2</sub>) as a bidentate ligand for Nb(V) as a metal center is presented. The different coordination behavior of caH<sub>2</sub> is well illustrated by a monomeric (Et<sub>4</sub>N)<i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)OPPh<sub>3</sub>]·3H<sub>2</sub>O.THF (<b>5</b>) and a novel tetranuclear compound (Et<sub>4</sub>N)<sub>4</sub>[Nb<sub>4</sub>O<sub>4</sub>(ca)<sub>2</sub>(<i>μ</i><sup>2</sup>-O)<sub>2</sub>Cl<sub>8</sub>]·2CH<sub>3</sub>CN (<b>6</b>) via self-assembly, respectively. These were obtained in >80% yields and characterized by IR, UV/Vis and NMR (<sup>1</sup>H, <sup>13</sup>C{<sup>1</sup>H}, <sup>31</sup>P{<sup>1</sup>H}) spectroscopy and single crystal X-ray diffraction, and they included a systematic assessment of the solid-state behavior. The anionic metal complexes showed different coordination modes at the Nb(V): [Nb<sub>4</sub>O<sub>4</sub>(ca)<sub>2</sub>(<i>μ</i><sup>2</sup>-O)<sub>2</sub>Cl<sub>8</sub>]<sup>4−</sup> (<b>6a</b>; distorted octahedral) and <i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)(OPPh<sub>3</sub>)]<sup>−</sup> (<b>5a</b>; <i>D</i><sub>5<i>h</i></sub> distorted pentagonal bipyramidal), respectively. The tetranuclear complex <b>6a</b> is substitution inert, while <i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)OPPh<sub>3</sub>]<sup>−</sup> (<b>5a</b>) allowed a systematic ligation kinetic evaluation. The substitution of the coordinated triphenylphosphine oxide by a range of pyridine-type entering nucleophiles, 4-<i>N</i>,<i>N</i>-dimethyl-aminopyridine (DMAP), pyridine (py), 4-methylpyridine (4Mepy), 3-chloropyridine (3Clpy) and 3-bromopyridine (3Brpy) in acetonitrile at 31.2 °C was carefully evaluated. The subtle interplay between the main group ligand systems and the hard, early transition metal Nb(V) complex (<b>5a</b>) was well illustrated. The entering monodentate ligands showed a 15-fold reactivity range increase in the order 3Brpy < 3Clpy < 4Mepy < py < DMAP in broad agreement with the Brønsted-donating ability of the nucleophiles. The activation parameters determined for the reaction of <b>5a</b> with DMAP as the entering ligand yielded Δ<i>H</i><sup>≠</sup><i><sub>k</sub></i><sub>f</sub> = 52 ± 1 kJ mol<sup>−1</sup> and Δ<i>S</i><sup>≠</sup><i><sub>k</sub></i><sub>f</sub> = −108 ± 3 J K<sup>−1</sup> mol<sup>−1</sup> for the enthalpy and entropy of activation, respectively, indicating an associative substitution mechanism. The study presents an important contribution to the structure/reactivity relationships in Nb(V) complexes stabilized by chloranilic acid as a bidentate ligand. |
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| spelling | doaj.art-c6c5d8fc2fc541979b831c07a934e57b2023-11-24T00:37:05ZengMDPI AGInorganics2304-67402022-10-01101016610.3390/inorganics10100166Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate LigandAlebel Nibret Belay0Johan Andries Venter1Orbett Teboho Alexander2Andreas Roodt3Department of Chemistry, Bahir Dar University, Bahir Dar P.O. Box 79, EthiopiaDepartment of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South AfricaDepartment of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South AfricaDepartment of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South AfricaChloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, caH<sub>2</sub>) as a bidentate ligand for Nb(V) as a metal center is presented. The different coordination behavior of caH<sub>2</sub> is well illustrated by a monomeric (Et<sub>4</sub>N)<i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)OPPh<sub>3</sub>]·3H<sub>2</sub>O.THF (<b>5</b>) and a novel tetranuclear compound (Et<sub>4</sub>N)<sub>4</sub>[Nb<sub>4</sub>O<sub>4</sub>(ca)<sub>2</sub>(<i>μ</i><sup>2</sup>-O)<sub>2</sub>Cl<sub>8</sub>]·2CH<sub>3</sub>CN (<b>6</b>) via self-assembly, respectively. These were obtained in >80% yields and characterized by IR, UV/Vis and NMR (<sup>1</sup>H, <sup>13</sup>C{<sup>1</sup>H}, <sup>31</sup>P{<sup>1</sup>H}) spectroscopy and single crystal X-ray diffraction, and they included a systematic assessment of the solid-state behavior. The anionic metal complexes showed different coordination modes at the Nb(V): [Nb<sub>4</sub>O<sub>4</sub>(ca)<sub>2</sub>(<i>μ</i><sup>2</sup>-O)<sub>2</sub>Cl<sub>8</sub>]<sup>4−</sup> (<b>6a</b>; distorted octahedral) and <i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)(OPPh<sub>3</sub>)]<sup>−</sup> (<b>5a</b>; <i>D</i><sub>5<i>h</i></sub> distorted pentagonal bipyramidal), respectively. The tetranuclear complex <b>6a</b> is substitution inert, while <i>cis</i>-[NbO(ca)<sub>2</sub>(H<sub>2</sub>O)OPPh<sub>3</sub>]<sup>−</sup> (<b>5a</b>) allowed a systematic ligation kinetic evaluation. The substitution of the coordinated triphenylphosphine oxide by a range of pyridine-type entering nucleophiles, 4-<i>N</i>,<i>N</i>-dimethyl-aminopyridine (DMAP), pyridine (py), 4-methylpyridine (4Mepy), 3-chloropyridine (3Clpy) and 3-bromopyridine (3Brpy) in acetonitrile at 31.2 °C was carefully evaluated. The subtle interplay between the main group ligand systems and the hard, early transition metal Nb(V) complex (<b>5a</b>) was well illustrated. The entering monodentate ligands showed a 15-fold reactivity range increase in the order 3Brpy < 3Clpy < 4Mepy < py < DMAP in broad agreement with the Brønsted-donating ability of the nucleophiles. The activation parameters determined for the reaction of <b>5a</b> with DMAP as the entering ligand yielded Δ<i>H</i><sup>≠</sup><i><sub>k</sub></i><sub>f</sub> = 52 ± 1 kJ mol<sup>−1</sup> and Δ<i>S</i><sup>≠</sup><i><sub>k</sub></i><sub>f</sub> = −108 ± 3 J K<sup>−1</sup> mol<sup>−1</sup> for the enthalpy and entropy of activation, respectively, indicating an associative substitution mechanism. The study presents an important contribution to the structure/reactivity relationships in Nb(V) complexes stabilized by chloranilic acid as a bidentate ligand.https://www.mdpi.com/2304-6740/10/10/166niobiumchloranilic acidsubstitutionmechanismkineticscrystal structures |
| spellingShingle | Alebel Nibret Belay Johan Andries Venter Orbett Teboho Alexander Andreas Roodt Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand Inorganics niobium chloranilic acid substitution mechanism kinetics crystal structures |
| title | Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand |
| title_full | Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand |
| title_fullStr | Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand |
| title_full_unstemmed | Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand |
| title_short | Synthesis, Single Crystal X-ray Structure, Spectroscopy and Substitution Behavior of Niobium(V) Complexes Activated by Chloranilate as Bidentate Ligand |
| title_sort | synthesis single crystal x ray structure spectroscopy and substitution behavior of niobium v complexes activated by chloranilate as bidentate ligand |
| topic | niobium chloranilic acid substitution mechanism kinetics crystal structures |
| url | https://www.mdpi.com/2304-6740/10/10/166 |
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