Reactivity of Calix-Tetrapyrrole SmII and SmIII Complexes with Acetylene: Isolation of an “N-Confused” Calix-Tetrapyrrole Ring

Dubé, Tiffany; Guan, Jingwen; Gambarotta, Sandro; Yap, Glenn P. A.

doi:10.1002/1521-3765(20010119)7:2<374::aid-chem374>3.0.co;2-e

Cited by 29 publications

(16 citation statements)

References 33 publications

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“…For this purpose, we focused on pyrrole‐based polyanions as ligands. These species have proved their ability both to stabilize low oxidation states in large cluster structures9 and to increase the high reactivity of the low‐valent compounds even further 2f–n. Here we describe the reduction of a tetravalent polypyrrolide thorium complex, which resulted in both solvent fragmentation and formation of the first divalent synthon thorium arene complex.…”

Section: Methodsmentioning

confidence: 93%

The First Thorium Arene Complex: A Divalent Synthon

2003

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Very strong reducing power [1] and a marked inclination toward performing cooperative attack on the same substrate [2] are the basis of the distinctive reactivity of divalent f-block metals. [3] In spite of the great interest in this field, divalent actinides remain basically unknown, possibly as a result of an intrinsic instability of this oxidation state. Moreover, the significance of the low oxidation states remains questionable, since the f electrons are expected to be more likely engaged in backbonding with the ligand rather than being metal-centered, nonbonding electrons. As a consequence, even simple salts such as UI 2 [4] and ThI 2[5] are regarded as divalent only from the point of view of formula, since the f electrons are believed to be located in a type of conduction band. Nevertheless, the electron-rich nature of these species raises expectations for high reactivity and strong reducing power. This idea is substantiated by the chemical behavior of the two known U II synthons, [6] and by some recent findings that a trivalent calix-tetrapyrrolide uranium compound resulted, upon reduction, in a complex series of transformations including dinitrogen cleavage, solvent deoxygenation, and depolymerization of silicone grease. [7] For thorium such chemistry is limited to a handful of trivalent compounds or synthons. [8] Given this scenario, we became interested in exploring the chemistry of divalent Th complexes, most likely synthons, with the dual purpose of: 1) probing the stability of an oxidation state unknown for thorium and 2) preparing potent two-electron reductants for further reactivity studies. For this purpose, we focused on pyrrole-based polyanions as ligands. These species have proved their ability both to stabilize low oxidation states in large cluster structures [9] and to increase the high reactivity of the low-valent compounds even further. [3f-n] Here we describe the reduction of a tetravalent polypyrrolide thorium complex, which resulted in both solvent fragmentation and formation of the first divalent synthon thorium arene complex.The reactions

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Section: Methodsmentioning

confidence: 93%

The First Thorium Arene Complex: A Divalent Synthon

2003

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“…28,29 Although pyrrolide ligands can coordinate to the metal centre in a k 1 mode through the N atom or in a k 5 mode, similar to classical cyclopentadienyl coordination to a metal, the k 1 mode is by far the more common of the two. 15,[30][31][32][33][34][35][36][37] The trans-calix[2]benzene[2]pyrrolide, (L) 2À , combines two pyrrolide heterocycles with two aryl rings connected via dimethylmethane linkers. 38 The lack of extended conjugation in this macrocycle, as compared to porphyrins, grants it a large degree of exibility, allowing the possibility of either sor p-bonding of the ligand to the metal centre through either the pyrrolide or arene.…”

Section: Introductionmentioning

confidence: 99%

Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes

et al. 2014

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“…The calix[4]tetrapyrrole tetraanion has proven to be a versatile ligand in the chemistry of low-valent Sm and U, having provided low-valent stable complexes with which a few aspects of molecular activation have been studied. A general characteristic of this ligand system seems to be a remarkable ability not only to stabilize a variety of low-valent species but also to increase the reactivity of the metal center with respect to the Cp counterparts.…”

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confidence: 99%

“…The “N-confused” 5a, or isomerized polypyrrolides are often encountered in the chemistry of polypyrroles and porphyrins, where they play an important role in the biochemistry of these systems . Variable amounts of the N-confused isomers may also be present as byproducts of the preparation of calix[4]tetrapyrroles and dipyrroles, usually requiring chromatographic purifications 13a.…”

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confidence: 99%