(Pyrazol-1-yl)carbonyl and Ester-Functionalized Bis(pyrazol-1-yl)methide Carbonyl Tungsten Complexes

Abstract

3,5-Dimethylpyrazol-1-yl)carbonyl-and n-butoxycarbonyl-functionalized bis(3,5-dimethylpyrazol-1-yl)methide carbonyl tungsten derivatives were unexpectedly formed, together with a bis(3,5-dimethylpyrazol-1-yl)acyl carbonyl tungsten complex, upon sequential treatment of bis(3,5-dimethylpyrazol-1-yl)methane with n-BuLi, tungsten carbonyl, and iodine. The resulting complexes were fully characterized using IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography. ■ INTRODUCTIONHeteroscorpionate ligands derived from bis(pyrazol-1-yl)-methane have been used extensively in recent years in coordination and bioinorganic chemistry, as well as being applied to a variety of catalytic transformations. 1 These ligands possess good donor properties and variable coordination modes, which allow them to form strong complexes with a wide variety of main-group and transition metals. Furthermore, the coordination behaviors of these ligands can be readily adjusted by making changes to the electronic and steric characteristics of the substituents on the pyrazolyl rings, as well as by changing the properties of the pendant arms. The deprotonation of the methylene bridge of bis(pyrazol-1-yl)methane 2 and the subsequent reaction of the resulting carbanionic species with various electrophilic reagents have been successfully exploited to synthesize these heteroscorpionate ligands. 3 The results of our previous study showed that the modification of bis(pyrazol-1-yl)methane with organometallic functional groups on the methine carbon resulted in unusual types of reactivity. 4 For example, the reaction of the tungsten carbonyl derivatives of trialkylstannylbis(3,5-dimethylpyrazol-1-yl)methane with iodine resulted in the formation of novel bis(pyrazol-1-yl)acyl complexes. 4a This result implied that pyrazolyl-based ligands could potentially be used to stabilize metal−acyl complexes, which are considered to be important active intermediates in many catalytic carbonylation processes. 5 The development of a technique for capturing these active species is highly desirable, because it would allow for the elucidation of their structures and the development of a better understanding of their role in catalytic processes, which could be used to design improved catalysts. The treatment of metal carbonyls with organolithium reagents leads to the formation of the corresponding acylmetalates, which usually form Fischer carbene complexes following their treatment with a hard electrophile. 6 In contrast, the treatment of these acylmetalates with a soft electrophile results in the formation of metal−acyl complexes. 6 As part of our ongoing interest in the reactivity of bis(pyrazol-1-yl)methide anion, 7 we herein report the reaction of bis(pyrazol-1-yl)methyllithium with tungsten carbonyl, followed by the reaction of the resulting intermediate with iodine, which yielded unexpected (pyrazol-1-yl)carbonyl and ester-functionalized bis(pyrazol-1-yl)methide tungsten derivatives, together with bis(pyrazol-1-yl)acyl tungste...

Copper-Based Complexes with Adamantane Ring-Conjugated bis(3,5-Dimethyl-pyrazol-1-yl)acetate Ligand as Promising Agents for the Treatment of Glioblastoma

“…Similarly, the planes passing through the acetylamido linker and each pyrazolyl ring makes with equatorial plane angles of 90 and 44.5°, respectively. A search in the CCDC repository , showed some Cu­(II) complexes of bis-pyrazolyl acetate, − among which few bis-pyrazolyl acetamide derivatives; other bis-pyrazolyl acetamide ligands, including the one present in the above-named aluminum complex are also known. − With one exception, reported bis-pyrazolyl acetate copper derivatives share a trans-fac coordination of the tridentate ligand with mean values of the O–Cu–O and O–Cu–N angles of 179.7 and 94.8°, similar to those found in this work. Likewise, the mean values of the Cu–N and Cu–O bonds are 2.055 and 2.276 Å; in 3 these bonds are 0.035 and 0.070 Å shorter than such means, respectively, but within the known ranges (1.972–2.438 Å for Cu–N and 1.936–2.540 Å for Cu–O).…”

“…The C1–O1 bond (1.231(4) Å) and the C1–C2 bond (1.549(4) Å) have in turn elongated double-bond and single-bond character, giving no evidence of conjugation outside the pyrazolyl rings. The C1–N1 and N1–C8 distances (1.316(4) and 1.481(4) Å, respectively), typical of an amide linkage, agree well with the mean values found for pyrazolyl acetamide ligands − (1.330, 1.457 Å) and even better if considering the same values specifically pertaining to acetamide ligands involved in coordination (1.322, 1.463 Å). ,,, …”

Study of the Coordination Modes of Hybrid NNCp Cyclopentadienyl/Scorpionate Ligands in Ir Compounds

“…The ligands based on the poly­(pyrazol-1-yl)­methane moiety are among the most versatile ligands as they are able to coordinate to a wide variety of metal centers . In particular, the chemistry of scorpionate ligands, based on bis­(pyrazol-1-yl)­methane, has been considerably extended in terms of their coordination chemistry − and catalytic applications. − In this field, a wide range of metal compounds supported by NNE-heteroscorpionate ligands (E = N, O, S) has been reported. − However, metal complexes which contain NNCp-heteroscorpionate ligands have been less studied. − This kind of ligand can be also seen as a linked cyclopentadienyl-donor ligand with great versatility in its coordination modes. Thus, hybrid cyclopentadienyl/heteroscorpionate ligands based on the bis­(pyrazol-1-yl)­methane moiety have shown different coordination modes in a range of metal complexes such as Li, Mg, group 3 and rare earth metals, group 4 metals, and Zn (Chart ).…”

Nickel and Platinum PCP Pincer Complexes Incorporating an Acyclic Diaminoalkyl Central Moiety Connecting Imidazole or Pyrazole Rings

“…Derivatives featuring a diaminoalkyl fragment coordinated to a transition metal, N 2 C­(H)–ML n , such as the ammonia activation product shown in Scheme , remain rare for five- and six-membered cyclic frameworks, where deprotonation with formation of NHC complexes (N 2 C → ML n ) prevails. They are more common for acyclic systems, most notably in strongly folded, nonclassical NCN pincer complexes with bis­(pyrazolyl)­methyl (Mo and W) and bis­(azaindolyl)­methyl (Pt) ligands.…”