Synthesis and Characterization of Potassium Complexes Containing Terminal η²‐Pyrazolato Ligands

Abstract

The potassium complexes [K(η2‐3,5‐R2pz)(η6‐18‐crown‐6)] (R = Ph, tBu; pz = pyrazolato) were prepared by treatment of 3,5‐diphenylpyrazole or 3,5‐di‐tert‐butylpyrazole with potassium hydride in the presence of 18‐crown‐6. These complexes contain η6‐18‐crown‐6 and terminal η2‐pyrazolato ligands, and constitute the first examples of group 1 metal complexes with this pyrazolato ligand coordination mode. In contrast to [K(η2‐3,5‐Ph2pz)(η6‐18‐crown‐6)] and [K(η2‐3,5‐tBu2pz)(η6‐18‐crown‐6)], the aqua complex [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] was obtained when 3,5‐dimethylpyrazole was treated with potassium hydride and 18‐crown‐6 in the presence of a small amount of water. [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] contains an η2‐pyrazolato ligand that is bent towards being co‐facial with the best plane of the 18‐crown‐6 ligand, to allow hydrogen bonding between the pyrazolato ligand nitrogen atoms and the coordinated aqua ligand. The hydrogen bonding thus confers a novel terminal π‐facial η2‐bonding mode to the pyrazolato ligand. All compounds were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

What is the Identity of the Metal Ions in the Active Sites of Coenzyme B12-Dependent Diol Dehydratase? A Computational Mutation Analysis

“…The error of 0.3 Å is not acceptable in the comparison of X-ray analysis and recent density functional theory. However, we have noticed that typical KsO bond distances of potassium-containing complexes is 2.8 Å, 18,19 as seen in the adenine-binding site ( Figure 1). Arsenate reductase from Staphylococcus aureus involves the seven-coordinate potassium site: the K + ion is coordinated by seven oxygen atoms originated from Asn13, Ser36, Thr63, Asp65, and two water molecules (PDB ID 1JF8).…”

Alkali‐Metal Pyrazolate Complexes with Unusual Pyrazolate Coordination Modes and Pseudocubane Motifs

“…It was suggested that this type of bonding should be common among Group 1 metal derivatives, and this was further supported by the subsequent isolation of the monomeric [K(η 2 ‐3,5‐Ph 2 pz)(η 6 ‐18‐crown‐6)] 7. Novel features of the potassium complexes include a case of π‐η 2 K coordination7 and examples of “slipped”, unsymmetrical η 2 binding, thus suggesting possible reversion to η 1 binding with the smaller Na + or Li + cations. Alternatively, if bridging prevails, the μ‐η 1 :η 2 :η 1 arrangement observed with potassium may be curtailed to the rare μ‐η 1 :η 2 mode, which has been observed only twice before 2g.…”

“…Although bridging coordination modes are still dominant in main‐group and d‐block transition‐metal pyrazolate complexes, recent advances in this field have found an increasing number of η 2 ‐coordinated complexes 3–5. 7, 8 The polynuclear potassium pyrazolato species obtained by Winter and co‐workers,2j [K(Ph 2 pz)(thf)] 6 , was the first structurally documented Group 1 complex to contain the η 2 pyrazolato coordination unit, which was incorporated into the then new μ 3 ‐η 1 :η 2 :η 1 arrangement. It was suggested that this type of bonding should be common among Group 1 metal derivatives, and this was further supported by the subsequent isolation of the monomeric [K(η 2 ‐3,5‐Ph 2 pz)(η 6 ‐18‐crown‐6)] 7.…”

“…7, 8 The polynuclear potassium pyrazolato species obtained by Winter and co‐workers,2j [K(Ph 2 pz)(thf)] 6 , was the first structurally documented Group 1 complex to contain the η 2 pyrazolato coordination unit, which was incorporated into the then new μ 3 ‐η 1 :η 2 :η 1 arrangement. It was suggested that this type of bonding should be common among Group 1 metal derivatives, and this was further supported by the subsequent isolation of the monomeric [K(η 2 ‐3,5‐Ph 2 pz)(η 6 ‐18‐crown‐6)] 7. Novel features of the potassium complexes include a case of π‐η 2 K coordination7 and examples of “slipped”, unsymmetrical η 2 binding, thus suggesting possible reversion to η 1 binding with the smaller Na + or Li + cations.…”

A Persistent Dipotassium 1,2,4‐Diazaphospholide Radical Complex: Synthesis, X‐Ray Structure, and Bonding

“…[17] The difference in bond length may be due to interactions with the [18]crown-6 ligands. [18] The angles between the plane of the 1,2,4-diazaphospholide C 2 N 2 P core and the approximate plane of the six oxygen atoms of the [18]crown-6 ligand average 868.…”