Syntheses and characterization of mu,eta(1),eta(1)-3,5-di-tert-butylpyrazolato derivatives of aluminum

An efficient one-pot synthesis of pyrazole complexes formed in situ: synthesis, crystal structure, Hirshfeld surface analysis and in vitro biological properties

The molecular crystals of monomeric and dimeric pyrazole complexes were prepared via one-pot syntheses. These are dichloridobis(3,5-dimethyl-1H-pyrazole-κN1)cobalt/zinc(0.2/0.8), [Co0.20Zn0.80Cl2(C5H8N2)2] or [Co0.2Zn0.8Cl2(3,5-dmp)2] (1), and bis(μ-3,5-dimethyl-1H-pyrazole)-κ2N1:N2;κ2N2:N1-bis[bromido/chlorido(0.7/0.3)bis(3,5-dimethyl-1H-pyrazole-κN1)cobalt/zinc(0.1/0.9)], [Co0.20Zn1.80Br1.40Cl0.60(C5H7N2)2(C5H8N2)2] or [Co0.1Zn0.9Br0.7Cl0.3(μ-3,5-dmp)(3,5-dmp)]2 (2). The isolated complexes contain 3,5-dimethylpyrazole (3,5-dmp) ligands formed in situ from the decomposition of 1-hydroxymethyl-3,5-dimethylpyrazole. In both isolated complexes, some positional disorder is observed at the metal ions and halogen ligands. The molecular crystals of 1 and 2 are centrosymmetric, with the space groups C2/c and P-1, respectively. Additionally, in the dinuclear complex, the pyrazole ring has a bridging coordination function with respect to the metal ions. Both complexes have good biological activities against cancer cells. The results of an in vitro cytotoxicity study indicated that compounds 1 and 2 showed significant cytotoxicity for cancer cell lines, including hepatic (HepG2 cells), lung (A549 cells) and colon cancer cells (SW 480 and SW 620). Based on the calculated IC50 values against human cancer cell lines, it was found that both complexes demonstrated potent antiproliferative activity combined with great selectivity towards cancer cells. Complex 2 was a more effective cytotoxic agent which, at the same time, exhibited high cytocompatibility. The obtained data are very encouraging and could be useful for anticancer drug discovery.

Synthesis and Structural Characterisation of Lithium, Zinc, and Aluminium Pyrazolate Complexes

The reaction of nBuLi with 3,5-dimethylpyrazole (Me2pzH) in Et2O or tmeda/hexane (tmeda=N,N,N′,N′-tetramethylethane-1,2-diamine) and with 3,5-dimethyl-4-nitropyrazolate (Me2pzHNO2) in THF results in the formation of three structurally diverse lithium pyrazolates: namely an Et2O-solvated tetrameric complex [Li4(Me2pz)4(OEt2)4], bridged entirely with μ-η2:η1-pyrazolate bonding, a hexanuclear complex [Li6(Me2pz)6(tmeda)2] with four different coordination modes (μ-η1:η1, μ-η2:η1, μ3-η1:η2:η1 and μ3-η2:η2:η1), and a new polymeric compound [Li2(Me2pzNO2)2(thf)2]n, with [Li2(Me2pzNO2)2(thf)2] groups linked by –NO2 coordination. A mononuclear zinc complex [Zn(tBu2pz)2(tBu2pzH)2].1/2THF (tBu2pzH=3,5-di-tert-butylpyrazole) was prepared by reaction of tBu2pzH with ZnEt2, unidentate tBu2pz groups being stabilised by N–H⋯N hydrogen bonding. Treatment of 3,5-diphenylpyrazole (Ph2pzH) with trimethylaluminium (mole ratio 3:1) in THF led to the formation of dinuclear [AlMe2(μ-Ph2pz)]2.1/2THF.

Reactions of α-diimine-aluminum complexes with sodium alkynides: versatile structures of aluminum σ-alkynide complexes

Reaction of AlCl(3) with the monoanionic α-diimine ligand [NaL] yielded the complex [L˙(-)Al(III)Cl(2)(-)] (1, L = [(2,6-iPr(2)C(6)H(3))NC(Me)](2)), and subsequent reduction of by sodium metal afforded the mononuclear [L(2-)Al(III)Cl(-)(THF)] (2) and binuclear [L(2-)(THF)Al(II)-Al(II)(THF)L(2-)] (3). Compounds 2 and 3 exhibit interesting reactivities to sodium alkynides at room temperature. Treatment of dialumane 3 with 1 equiv. of 4-methylphenylacetylene in the presence of sodium metal yielded the asymmetric Al-Al-bonded compound [Na(Et(2)O)][LAl-Al(C[triple bond, length as m-dash]C(C(6)H(4)-Me))L] (4) containing an alkynyl group attached to one of the Al atoms. The reaction of 2 with 4-methylphenylacetylene and Na (or sodium 4-methylphenylacetylide) resulted in the mononuclear product [L(THF)Al(C[triple bond, length as m-dash]C-(C(6)H(4)-Me))] (5) containing a single terminal acetylide ligand. Precursor 2 reacted with 2 equiv. of phenylacetylene (or 4-methylphenylacetylene, trimethylsilylacetylene) and Na to give the tweezer "ate" complexes, [Na(THF)(DME)][LAl(C[triple bond, length as m-dash]CR)(2)] (R = C(6)H(5), ; C(6)H(4)-Me, ; Si(Me)(3), 6c), [Na(THF)](2)[LAl(C[triple bond, length as m-dash]CPh)(2)](2)(μ-C(7)H(8)) (7), [Na(C(7)H(8))][(μ-Na)][LAl(C[triple bond, length as m-dash]CSi(Me)(3))(2)](2) (8), as well as the polymeric [LAl(C[triple bond, length as m-dash]CPh)(2)Na](n) (9). In the products, two alkynyl groups coordinate terminally to one Al center and a sodium ion is embedded between these two alkynyls. Interestingly, both cycloaddition and terminal acetylide coordination of three equiv. of alkyne occurred in the reaction of with 1-hexyne, resulting in the unique dialuminum complex [Na(Et(2)O)](2)[{L(C(C(4)H(9))[double bond, length as m-dash]CH)}Al(C[triple bond, length as m-dash]C(C(4)H(9)))(2)](2) (10). Complexes 1-10 have been characterized by NMR ((1)H, (13)C) and IR spectroscopy, elemental analysis, and X-ray diffraction, and their electronic structures were studied by DFT calculations.

Aluminum Dimer Containing Bulky 1,2,3-Triazolate Ligand

The first molecular aluminum 1,2,3-triazolato complex was synthesized bearing a bulky 1,2,3-triazolate ligand. Oligomers and polymers were avoided due to the bulkiness and noncoordinating nature of the substituents. The novel Al2N4ring formed contains symmetrical Al-N bond distances unexpectedly having asymmetric Al-N-N angles of 144.55(15)° and 115.83(14)°. This asymmetry demonstrates the effect of the steric hindrance of the ligand.

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

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.

Synthesis of Carbaalane Halogen Derivatives

The carbaalane halogen derivatives [(AlX)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (X = F (9), Cl (7), Br (10), I (11)) were prepared in toluene from [(AlH)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (6) and BF(3).OEt(2), BX(3) (X = Br, I), Me(3)SnF, and Me(3)SiX (X = Cl, Br, I), respectively. A partially halogenated product [(AlH)(2)(AlX)(4)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (12) (X = Cl (approximately 40%), Br (approximately 60%)) was obtained from 5 and impure BBr(3). [(AlH)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (5) was converted to [(AlX)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (X = F (13), Cl (14), Br (15), I (16)) using BF(3).OEt(2) and Me(3)SiX (X = Cl, Br, I), respectively. The X-ray single-crystal structures of 11.C(6)H(6), 12.3C(7)H(8), 13.6C(7)H(8), and 15.4C(7)H(8) were determined. Compounds 7 and 9-11 are soluble in benzene/toluene and could be well characterized by NMR spectroscopy and MS (EI) spectrometry. The results demonstrate the facile substitution of the hydridic hydrogen atoms in 5 and 6 by the halides with different reagents.