Tris(Pyrazolyl)Methane Ligands: The Neutral Analogs of Tris(Pyrazolyl)Borate Ligands

Anticancer potential of NSAID-derived tris(pyrazolyl)methane ligands in iron(II) sandwich complexes

Tris(pyrazolyl)methane (tpm), 2,2,2-tris(pyrazolyl)ethanol (tpmOH) and its esterification derivatives with ibuprofen and flurbiprofen (tpmIBU and tpmFLU) were used as ligands to obtain complexes of the type [Fe(tpmX)2]Cl2 (1-4). The tpmIBU and tpmFLU ligands and corresponding complexes 3 and 4 were characterized by IR and multinuclear NMR spectroscopy, and the structure of tpmIBU was elucidated by single crystal X-ray diffraction. Complexes 1-4 were also assessed for their behaviour in aqueous media (solubility in D2O, octanol/water partition coefficient, stability in physiological-like conditions). The antiproliferative activity of ligands and complexes was determined on A2780, A2780cis and A549 cancer cell lines and the non-cancerous HEK 293T and BJ cell lines. The ligands and complexes were investigated for their ability to inhibit COX-2 (cyclooxygenase) and HNE (4-hydroxynonenal) enzymes. Complexes 3 and 4 exhibited cytotoxicity that may be attributed predominantly to their bioactive fragments, while DNA binding and enhancement of ROS production do not appear to play any significant role.

Ruthenium(II)-Tris-pyrazolylmethane Complexes Inhibit Cancer Cell Growth by Disrupting Mitochondrial Calcium Homeostasis

While ruthenium arene complexes have been widely investigated for their medicinal potential, studies on homologous compounds containing a tridentate tris(1-pyrazolyl)methane ligand are almost absent in the literature. Ruthenium(II) complex 1 was obtained by a modified reported procedure; then, the reactions with a series of organic molecules (L) in boiling alcohol afforded novel complexes 2–9 in 77–99% yields. Products 2–9 were fully structurally characterized. They are appreciably soluble in water, where they undergo partial chloride/water exchange. The antiproliferative activity was determined using a panel of human cancer cell lines and a noncancerous one, evidencing promising potency of 1, 7, and 8 and significant selectivity toward cancer cells. The tested compounds effectively accumulate in cancer cells, and mitochondria represent a significant target of biological action. Most notably, data provide convincing evidence that the mechanism of biological action is mediated by the inhibiting of mitochondrial calcium intake.

Anticancer ruthenium(ii) tris(pyrazolyl)methane complexes with bioactive co-ligands

New anticancer RuII-tpm complexes are presented, including a synthetic strategy to tether bioactive molecules to the metallic scaffold.

Phosphine-functionalised tris(pyrazolyl)methane ligands and their mono- and heterobimetallic complexes

The synthesis, characterisation and reactivity of new phosphine-functionalised tris(pyrazolyl)methane ligands (TpmPR₂, 2a-c, with R = Ph, nBu, iPr) are presented. The reaction of 2a-c with [Rh(CO)₂Cl]₂ furnished N,P-heterochelate carbonyl complexes (3a-c), which were used to quantify the donor abilities of the ligands via IR spectroscopy. The coordination flexibility was demonstrated by treating representative members of this new ligand class with [CpRu(acn)₃][PF₆] (acn = acetonitrile), [(tht)AuCl] (tht = tetrahydrothiophene) and [Pd(allyl)Cl]₂ providing either a N,N,P-heteroscorpionate complex (4) or the P-coordinated complexes (5,6) without any involvement of the pyrazolyl entities. With 2a and [Pd(cod)Cl₂], another P,N-heterochelate complex (7) was obtained, which served as a precursor for a heterobimetallic complex containing palladium and copper (8). Detailed NMR spectroscopic and X-ray crystallographic investigations have been performed on all new complexes.

Hydrosoluble Complexes Bearing Tris(pyrazolyl)methane Sulfonate Ligand: Synthesis, Characterization and Catalytic Activity for Henry Reaction

The catalytic activity of the water-soluble scorpionate coordination compounds [Cu(-NN’O-Tpms)2] (1), [Mn(Tpms)2] (2) and Li[FeCl2(-NN’N’’-Tpms)] (3) [Tpms = tris(pyrazolyl)-methane sulfonate, O3SC(pz)3], were studied towards the (Henry) reaction between benzaldehyde and nitromethane or nitroethane in aqueous medium to afford, respectively, 2-nitro-1-phenylethanol or 2-nitro-1-phenylpropanol, the latter in the syn and the anti diastereoisomeric forms. Complex 1 exhibited the highest activity under the optimum experimental conditions and was used to broaden the scope of the reaction to include several aromatic aldehydes achieving yields up to 94%.

Multiple coordination modes of a new ditopic bis(pyrazolyl)methane-based ligand

A new ditopic ligand, N-(2,2-bis(pyrazolyl)ethyl)-2,2-bis(pyrazolyl)acetamide ((pz)₂CH-C(O)-NH-CH₂-CH(pz)₂, L4Pz, pz = pyrazolyl ring), comprising two bis(pyrazolyl)methane donor groups linked via an amide bridge, has been prepared from the reaction of HOOCCH(pz)₂ and H₂NCH₂CH(pz)₂. The ligand coordinates to various metallic salts (i.e. AgO₃SCF₃, PdCl₂, Re(CO)₅Br, and Fe(BF₄)₂), in either a κ²-μ-κ² or a κ³-μ-κ² fashion, depending on the coordination preferences of the metallic center. These compounds were characterized by NMR, UV-Vis and IR spectroscopy, and in solid state by single crystal X-ray diffraction. In the case of silver(i), a mono-dimensional coordination polymer was obtained, while the others were found to be discrete complexes. The synthesis and characterization of a heterobimetallic complex is also described. In solid state, all compounds are associated into supramolecular architectures via hydrogen bonding and pyrazolyl embrace interactions.

Magnesium Stung by Nonclassical Scorpionate Ligands: Synthesis and Cone-Angle Calculations

A series of tris(pyrazolyl)alkane (RCTp) scorpionate ligands of the type RCTp^3-R' (R=Me, nBu, SiMe₃ ; R'=H, Me, Ph, iPr, tBu) were synthesized and their ability to coordinate methylmagnesium moieties was examined. The reaction of Mg(AlMe₄ )₂ with neutral proligands HCTp^3-Ph or Me₃ SiCTp^3-Me , containing a non-innocent backbone methine moiety, led to deprotonation/rearrangement and SiMe₃ /AlMe₃ exchange to afford [(Me₃ AlCTp^3-Ph )₂ Mg] and [(Me₃ AlCTp^3-Me )Mg(AlMe₄ )], respectively, with monoanionic tripodal ligands. Treatment of sterically less demanding RCTp^3-R' with Mg(AlMe₄ )₂ produced isostructural dicationic "metal-in-a-box" complexes of the type [(RCTp^3-R' )₂ Mg][AlMe₄ ]₂ (R=Me, nBu; R'=H, Me). Utilization of the superbulky ligands MeCTp^3-Ph and MeCTp^3-tBu gave monocationic complexes [(MeCTp^3-Ph )MgMe][AlMe₄ ] and [(MeCTp^3-tBu )MgMe][Al₂ Me₇ ] as separated ion pairs. The reaction of Mg(AlMe₄ )₂ with nBuCTp^3-Ph led to the formation of the dimagnesium complex [{(nBuCTp^3-Ph )Mg(AlMe₄ )}₂ (μ-CH₃ )], which features a bridging methyl moiety and terminal η¹ -coordinated tetramethylaluminato ligands. Isopropyl-substituted ligand MeCTp^3-iPr emerged from further fine-tuning of the steric and electronic parameters and, upon reaction with Mg(AlMe₄ )₂ , gave (MeCTp^3-iPr )Mg(AlMe₄ )₂ ; this represents the first example of a magnesium bis(alkyl) complex with an intact RCTp^3-R' ligand. The exact ligand cone angles Θ^° of all magnesium complexes were determined according to the mathematical analysis developed by Allen et al. [J. Comput. Chem. 2013, 34, 1189-1197].

Reaction Chemistry of Silver(I) Trifluoromethanesulfonate Complexes of Nitrogen-Confused C-Scorpionates

Two new C-scorpionate ligands with a bis(3,5-dimethylpyrazol-1-yl)methyl group bound to the 3 position of either an N-tosyl (^TsL*) or an N-H pyrazole (^HL*) ring have been prepared. The silver(I) complexes of these new ligands and the two previously reported analogous ligands with unsubstituted bis(pyrazol-1-yl)methyl groups (^TsL and ^HL) in both 1:1 and 2:1 ligand/metal ratios were investigated to explore the effects of ligand sterics on their physical and chemical properties. The structurally characterized derivatives of the type [Ag(L)₂](OTf) are four-coordinate, where the confused pyrazolyl is not bound to the metal. On the other hand, three 1:1 complexes [Ag(L)](OTf) had all pyrazolyls bound, while the μ-κ¹,κ¹-^TsL derivative had an unbound confused pyrazolyl. The molecularity of the latter four ranged from polymeric to dimeric to monomeric in the solid with increasing steric bulk of the ligand. The utility of these complexes in stoichiometric ligand-transfer reactions and in styrene aziridination was demonstrated. Thus, tricarbonylmanganese(I) complexes were prepared as kinetically inert models for comparative solution diffusion NMR studies. Also, [Fe(^HL)₂](OTf)₂ was prepared for similar reasons and to compare the effects of anion on spin-crossover properties.

Novel Cu(ii) complexes with NNO-Schiff base-like ligands – structures and magnetic properties

The X-ray structures and magnetic properties of 22 copper(ii) complexes, derived from six new tridentate Schiff base-like ligands and various conterions, are discussed.

Monoanionic, Bis(pyrazolyl)methylborate [(Ph3B)CH(3,5-(CH3)2Pz)2)]- as a Supporting Ligand for Copper(I)-ethylene, cis-2-Butene, and Carbonyl Complexes

The monoanionic bidentate ligand [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]^- has been prepared from lithium bis(pyrazolyl)methanide and triphenylborane. This useful new ligand is closely related to the well-established bis(pyrazolyl)borate and bis(pyrazolyl)methane ligands but has key differences to both analogues as well. The ethylene, cis-2-butene, and carbon monoxide adducts [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(L) (where L = C₂H₄, cis-CH₃HC═CHCH₃, and CO) have been prepared from [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Li(THF), copper(I) triflate, and the corresponding coligand. These complexes have been characterized by NMR spectroscopy and X-ray crystallography. In all cases the bis(pyrazolyl) moiety is bound in κ²N fashion with the BPh₃ group rotated to sit over the metal center, sometimes coordinating to the metal via phenyl carbons as in [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Li(THF) and [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(CO) or simply hovering above the metal site as in [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(C₂H₄) and [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(cis-CH₃HC═CHCH₃). The ¹³C and ¹H resonances of the ethylene carbon and protons of [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(C₂H₄) appear at δ 81.0 and 3.71 ppm in CD₂Cl₂, respectively. The characteristic CO frequency for [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(CO) has been observed at υ̅ 2092 cm^-1 by infrared spectroscopy and is lower than that of free CO suggesting moderate M → CO π-back-donation. A detailed analysis of these complexes has been presented herein.

Group 9 and 10 complexes with the bidentate di(1H-indazol-1-yl)methane and di(2H-indazol-2-yl)methane ligands: synthesis and structural characterization

Ni, Pd and Co bis(indazol-1-yl)methane complexes assemble into 3D-networks based on intermolecular electrostatic, H-bonds and aromatic interactions.

Green protection of pyrazole, thermal isomerization and deprotection of tetrahydropyranylpyrazoles, and high-yield, one-pot synthesis of 3(5)-alkylpyrazoles

3(5)-Alkylpyrazoles are obtained in high yield from pyrazole by a one-pot procedure.

Heterometallic complexes with cube-type [MTi3N4] cores containing Group 10 metals in a variety of oxidation states

The metalloligand [{Ti(η⁵-C₅Me₅)(μ-NH)}₃(μ₃-N)] is capable of stabilizing Group 10 metals in the oxidation states 0,iioriv.

Heterocyclic substituted methanides as promising alternatives to the ubiquitous nacnac ligand

A series of group 13 complexes containing deprotonated bisheterocyclomethanes have been prepared as well as structurally and spectroscopically characterised.

Direct synthesis of the Janus-head ligand (MePy)3Sn–Sn(MePy)3using an unusual pyridyl-transfer reaction (MePy = 6-methyl-2-pyridyl)

Thein situreaction of the tripodal anion [EtAl(^MePy)₃]⁻(^MePy = 6-Me-2-py) with SnCl₂gives the Janus-head ligand (^MePy)₃Sn–Sn(^MePy)₃, containing a Sn–Sn bond, through a novel, one-pot reaction involving a combination of pyridyl transfer and metal-oxidation.

Copper(I) and silver(I) complexes supported by the tridentate [{Ti(η(5)-C5Me5)(μ-NH)}3(μ3-N)] metalloligand

Copper(I) and silver(I) ionic compounds [(L)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] containing [MTi(3)N(4)] cube-type cations have been prepared by reaction of [(CF(3)SO(2)O)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}] (M = Cu (2), Ag (3)) with a variety of donor molecules L. Treatment of complexes 2 and 3 with NH(3) in toluene at room temperature gives the ammonia adducts [(H(3)N)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (M = Cu (4), Ag (5)), whose X-ray crystal structures reveal two cube-type cations associated through hydrogen bonding interactions between the ammine ligands and one oxygen atom of each trifluoromethanesulfonate anion. Analogous treatment of 2 and 3 with 1 equiv of pyridine, 2,6-dimethylphenylisocyanide, tert-butylisocyanide, or triphenylphosphane gives the ionic compounds [(L)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (L = py, M = Cu (6), Ag (7); L = CNAr, M = Cu (8), Ag (9); L = CNtBu, M = Cu (10), Ag (11); L = PPh(3), M = Cu (12), Ag (13)). The reactions of 2 and 3 with methylenebis(diphenylphosphane) (dppm) in a 1:1 ratio lead to the single-cube complexes [(dppm)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (M = Cu (14), Ag (15)), whereas in a 2:1 ratio give the bisphosphane-bridged double-cube compounds [{M(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}(2)(μ-dppm)][O(3)SCF(3)](2) (M = Cu (16), Ag (17)). Similarly, treatment of 2 or 3 with a half equivalent of ethane-1,2-diylbis(diphenylphosphane) (dppe) affords double-cube derivatives [{M(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}(2)(μ-dppe)][O(3)SCF(3)](2) (M = Cu (18), Ag (19)). The X-ray crystal structures of 4, 5, 10, 14, 15, and 18 have been determined.