Zinc Pyrazolylborate Complexes with Phenoxide and Alkoxide Ligands

Walz, Rainer; Weis, K. H.; Ruf, Michael; Vahrenkamp, Heinrich

doi:10.1002/cber.19971300727

Cited by 35 publications

(36 citation statements)

References 19 publications

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“…5, the cobalt atom is in pseudotetrahedral environment and is coordinated by the tridentate pyrazolylborate ligand and a monodentate 4-nitrophenolate anion. The Co1-O61 bond distance is 1.890(5) Å which is slightly longer than the Zn-O bond distance (1.860 (2) Å ) in reported 4-nitrophenolate complex of zinc [35] and also than Co-O bond length in complex 4. The Co-N bond distances in present complex are Co1-N42; 2.022 (6), Co2-N(2); 2.024 (5), and Co1-N22; 2.042 (5) Å and are very similar to the Zn-N bond distances (Zn-N1, 2.015(2); Zn-N2, 2.024(2); Zn-N3, 2.051(2) Å ) in zinc-nitrophenolate complex [35].…”

Section: Hydrolysis Of Estersmentioning

confidence: 64%

“…The Co1-O61 bond distance is 1.890(5) Å which is slightly longer than the Zn-O bond distance (1.860 (2) Å ) in reported 4-nitrophenolate complex of zinc [35] and also than Co-O bond length in complex 4. The Co-N bond distances in present complex are Co1-N42; 2.022 (6), Co2-N(2); 2.024 (5), and Co1-N22; 2.042 (5) Å and are very similar to the Zn-N bond distances (Zn-N1, 2.015(2); Zn-N2, 2.024(2); Zn-N3, 2.051(2) Å ) in zinc-nitrophenolate complex [35]. The Co1-O61-C62 bond angle (151.3(3)°) is larger than Zn-O-C 132.6(2)°in zinc-nitrophenolate [35].…”

Section: Hydrolysis Of Estersmentioning

confidence: 64%

“…The Co-N bond distances in present complex are Co1-N42; 2.022 (6), Co2-N(2); 2.024 (5), and Co1-N22; 2.042 (5) Å and are very similar to the Zn-N bond distances (Zn-N1, 2.015(2); Zn-N2, 2.024(2); Zn-N3, 2.051(2) Å ) in zinc-nitrophenolate complex [35]. The Co1-O61-C62 bond angle (151.3(3)°) is larger than Zn-O-C 132.6(2)°in zinc-nitrophenolate [35]. The reaction of 2 with 4-nitrophenyltrifluoroacetate (Scheme 3) resulted the formation of complex 7.…”

Section: Hydrolysis Of Estersmentioning

confidence: 69%

“…The cobalt(II) atom is octahedrally coordinated by the tripodal anionic pyrazolylborate ligand, a 4-nitrophenolate anion and two acetonitrile ligands bound in a cisoid fashion. The cobalt-nitrogen bond distances from the tris(pyrazolyl)borate ligand are (Co1-N1, 2.147(4); Co1-N3, 2.140(4); Co1-N5, 2.144(5) Å , which is longer than the Co-N bond distances in four coordinated cobalt-nitrophenolate complex having HB(3- bonded cobalt-nitrophenolate complex but larger than Zn-O-C (132.6(2)°) in zinc-nitrophenolate [35].…”

Section: Hydrolysis Of Estersmentioning

confidence: 88%

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A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

Babbar

Tyagi

Weyhermüller³

2008

Transition Met Chem

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A novel Co(II) hydroxo complex Co{HB(3- Prpz) 3 = hydrotris(3-tert-butyl-5-isopropylpyrazol-l-yl)borate} has been prepared and its molecular structure has been determined by X-ray crystallography. This complex is mononuclear with distorted tetrahedral geometry. The reaction of CO 2 with Co{HB(3- Prpz) 3 }] 2 (CO 3 ) wherein the carbonate group is bound to both metal centers in an asymmetrical manner. In order to explore the role of labile metal complexes in promoting ester hydrolysis, complexes [Co{HB(3,

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Section: Hydrolysis Of Estersmentioning

confidence: 64%

Section: Hydrolysis Of Estersmentioning

confidence: 64%

Section: Hydrolysis Of Estersmentioning

confidence: 69%

Section: Hydrolysis Of Estersmentioning

confidence: 88%

See 2 more Smart Citations

A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

Babbar

Tyagi

Weyhermüller³

2008

Transition Met Chem

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“…The resulting phenolate complexes 10 ± 12 have also been characterized by us before. [48,51] All reactions described here are strictly stoichiometric, that is, they are finished after one turnover. Although they produce one equivalent of water this does not initiate a catalytic cycle, for example, by liberation of the phosphate ligand as the corresponding phosphoric acid and re-formation of the [Tp'ZnÀOH] complex.…”

Section: Organophosphate Cleavagesmentioning

confidence: 99%

Evidence for a Trajectory of Hydrolytic Reactions brought about by [L3Zn−OH] Species

et al. 1999

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A kinetic study has been performed on the hydrolytic cleavage of various triorganophosphates PO-(OR) 2 (OR') by three pyrazolylborate ± zinc hydroxide complexes [Tp'Zn À OH] to form [Tp'Zn À OPO(OR) 2 ] and HOR'. The nature of the reactions (first order both in the zinc complex and the phosphate) and the strongly negative activation entropies (À 54 to À 126 J mol) indicate an intimate association of the ZnÀOH and PO functions in the rate-determining step. Some ester cleavages by [Tp'Zn À OH] show the same kinetic pattern and similar activation parameters. The observations are in accord with a four-center arrangement (ZnOPO or ZnOCO) in the activated complex, that is, the hybrid mechanism discussed for zinc enzyme as well as zinc complex catalyzed hydrolyses. A trajectory for reactions passing through this intermediate has been constructed with the Bürgi ± Dunitz structure correlation method, based on the geometries of 30 [Tp'Zn(X)(Y)] species with truly five-coordinate zinc centers. Its first step is the approach of the substrates oxygen atom to the tetrahedral L 3 ZnÀOH species along the axis of a trigonal bipyramid. In the resulting four-center intermediate with five-coordinate zinc a Berry pseudorotation describes the synchronous formation of the Zn À O-(substrate) and breaking of the ZnÀO-(OH) bonds. The concluding step in the coordination sphere of zinc is the expulsion of the former OH oxygen, now part of the substrate, again along the axis of a trigonal bipyramid. This mechanism, which is applicable to phosphate as well as to ester, amide, and carbon dioxide hydrolysis, is in accord with theoretical models of carbonic anhydrase action.

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(Pyrazolylborate)zinc Organophosphate Complexes Resulting from Hydrolytic Cleavage of Phosphate Esters

Weis¹,

Rombach²,

Ruf³

et al. 1998

Eur. J. Inorg. Chem.

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Five different (pyrazolylborate)zinc hydroxide complexes Tp*Zn−OH (1) were used as hydrolytic reagents towards esters of various acids of phosphorus. Trimethyl phosphate and trimethyl phosphite could not be cleaved. Dimethyl and diphenyl phosphite yielded TptBu,MeZn−OPHO(OR) (2, 3). Triphenyl phosphate reacted slowly producing moderate yields of Tp*Zn−OPO(OPh)2 (4). Tris(p‐nitrophenyl) phosphate was cleaved rapidly, forming Tp*Zn−OPO(OC6H4NO2)2 (5) and Tp*Zn−OC6H4NO2 (6). Alkylbis(p‐nitrophenyl) phosphates showed intermediate reactivity, losing p‐nitrophenolate upon hydrolysis and producing Tp*Zn−OPO(OR)(OC6H4NO2) (7, 8). When phosphorus acid diesters were employed, condensation between the Zn−OH and P−OH functions occurred. This proved to be the convenient way of preparing the organophosphate complexes Tp*Zn−OPO(Ph)2 (9), Tp*Zn−OPO(OPh)2 (4), and Tp*Zn−OPO(OC6H4NO2)2 (5). Six structure determinations showed the structural variability of the resulting complexes.

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Zinc Pyrazolylborate Complexes with Phenoxide and Alkoxide Ligands

Cited by 35 publications

References 19 publications

A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

Evidence for a Trajectory of Hydrolytic Reactions brought about by [L3Zn−OH] Species

(Pyrazolylborate)zinc Organophosphate Complexes Resulting from Hydrolytic Cleavage of Phosphate Esters

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