3,5-Dimethyl and 3,5-Di-tert-butylpyrazolato Complexes with Alkali Metals:  Monomeric, Dimeric, Cluster, and 1D Chain Structures

Abstract

The pyrazolato complexes [(Me(2)pz)(THF)Li] (1), [((t)Bu(2)pz)Li](4) (2), [((t)Bu(2)pzH)((t)()Bu(2)pz)Li](2) (2a), [(Me(2)pz)Na] (3), [((t)Bu(2)pz)Na](4), [((t)Bu(2)pz)(6)(OH)Na(7)] (4a), [((t)Bu(2)pz)(18-crown-6)Na] (4b), and [((t)Bu(2)pz)K] (5) were synthesized by metalation reactions between R(2)pzH (R = Me, (t)()Bu) and alkyllithium, elemental sodium, or potassium. All the complexes were characterized by spectroscopic methods and microanalysis, and in addition, the crystal structures of 2, 2a, 3, 4a, 4b, and 5 were obtained by single-crystal X-ray diffraction. They show monomeric, dimeric, cluster, and 1D chain structures in the solid state. Ab initio calculations on the structure and stabilities of the monomeric pzM complexes were performed at the MP2 level of theory showing good agreement with the coordination preferences of the pyrazolato ligand to a particular alkali ion.

Substitution effects in N-pyrazole and N-imidazole derivatives along the periodic table

“…In the case of the pyrazoles and imidazoles substituted by alkaline and alkaline-earth elements, two different minima structures have been found, one interacting with the nitrogen atom and the second one above the ring interacting with its p-cloud, in agreement with recent theoretical and experimental reports [25,26]. The first minima is the global minima in the case of the pyrazoles and alkaline-earth derivatives of the imidazoles while in the case of the alkaline derivatives of the imidazoles the global minima is the second one.…”

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

“…X‐ray crystallography confirmed the formation of an Et 2 O‐solvated dimeric lithium pyrazolate complex (Figure 1 a), with two four‐coordinate lithium ions bridged by two pyrazolate ligands bound in an η 2 fashion to one lithium ion and η 1 to the other. Thus, 1 has the highly unusual (pyrazolate) coordination of μ‐η 2 :η 1 ,2g, 9 which is reminiscent of carboxylate10 and formamidinate11 chemistry.…”

“…These complexes illustrate the wide variety of coordination modes possible for pyrazolate ligands, including the appearance of three new binding modes, with 2 and 4 providing variations on the cubane structural theme. Since this work was completed, a number of related lithium and sodium pyrazolates have been reported 9. We also report the structures of oxo‐centered M 8 cages [( t Bu 2 pz) 6 Li 8 O] ( 5 ) and [( t Bu 2 pz) 6 Na 8 O] ( 6 ), obtained as by‐products.…”

“…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. 9…”

Improved Synthesis and Detailed Characterization of a Hybrid Pyrazole‐TACN Dinucleating Ligand

“…In the solid state the pyrazolato unit in NaL displays an unusual μ 2 -η 2 :η 1 bridging mode, leaving one side arm completely uncoordinated. While such coordination is rarely observed with compartmental pyrazole ligands such as HL, [29] sodium cation complexes formed with simple 3,5-di-alkyl-substituted pyrazole units (alkyl = methyl, [53,54] phenyl, [55] or tertbutyl [53,[55][56][57][58] ) show a diverse range of binding motifs. For example, structural determination of the sodium cation complex [55] Indeed, the pyrazole ring has been referred to as the "most flexible ligand group in coordination chemistry" and displays no fewer than 20 different coordination modes.…”