The First Homoleptic Metallabenzene Sandwich Complex

Englert, Ulli; Podewils, Frank; Schiffers, Ingo; Salzer, Albrecht

doi:10.1002/(sici)1521-3773(19980817)37:15<2134::aid-anie2134>3.3.co;2-k

Cited by 5 publications

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“…Recently, Salzer succeeded in generating the first example of a homoleptic metallabenzene sandwich compound, 28 (Scheme ). This was accomplished by treating the open ruthenocene C with Ru 3 (CO) 12 at 145 °C.…”

Section: Other Metal-coordinated Metallabenzenesmentioning

confidence: 99%

Metallabenzenes

2001

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Many similarities exist between metallabenzenes and conventional arenes. Among these similarities are structural features such as ring planarity and the absence of bond length alternation, spectroscopic features such as downfield chemical shifts for ring protons, and chemical reactions such as electrophilic aromatic substitution and arene displacement from (arene)Mo(CO)3. All of these features, taken together, strongly support the thesis that metallabenzenes represent a new class of aromatic compounds, one in which metal d orbitals participate fully with carbon p orbitals in the formation of ring pi-bonds. However, it is also apparent that metallabenzenes are much more prone to isomerization reactions than are conventional arenes. This appears to be particularly true of first-row and second-row metallabenzenes, where the metal-carbon bond strengths are weaker. In these systems, carbene migratory insertion often leads to cyclopentadienyl-metal products. pi-Coordination of metallabenzenes to other metal centers generally stabilizes the metallabenzene moieties while maintaining their aromatic character. Among metallabenzenes coordinated in this way, there are representatives from all three transition-metal rows (Fe, Ni, Mo, Ru, and Ir). The metal atom in pi-coordinated metallabenzenes is displaced out of the ring and away from the complexing metal center. The reason for this displacement in most cases appears to be steric repulsion between ligands on the two metal centers. However, other subtle effects may contribute. For example, metal displacement leads to more favorable internal angles at the alpha-carbons and a better orientation of C alpha p orbitals toward the complexing metal center. While no dominant synthetic strategy for constructing metallabenzenes has emerged, cyclization reactions involving metal-thiocarbonyl, metal-alkylidyne, and metal-alkylidene precursors have proved useful. In addition, approaches involving pentadienyl reagents as the source of ring carbons have yielded notable successes. Vinylcyclopropene reagents have recently led to isolation of the first example of a metallabenzene valence isomer--a metallabenzvalene--and its subsequent conversion to a planar metallabenzene. Finally, interligand attacks of butadienyls on carbonyls have produced a variety of transient oxy- or alkoxy-substituted metallabenzene species. The development of new synthetic approaches, particularly systematic approaches that can be used with a variety of transition metals, is the key issue facing metallabenzene chemists. One hundred and thirty-five years after Kekulé's celebrated dream, aromatic chemistry continues to be a fascinating and provocative research topic. Metallabenzenes represent one of the "new frontiers" that promise to keep aromatic chemistry vibrant well into the 21st century.

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Section: Other Metal-coordinated Metallabenzenesmentioning

confidence: 99%

Metallabenzenes

2001

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“…For example, metallabenzene 21 can undergo typical aromatic electrophilic substitution reactions with Cu(NO 3 ) 2 and Br 2 to give 22 and 23, respectively (Scheme 5). 8 Like benzene, metallabenzenes can also function as η 6 -ligands to form half-sandwich (e.g., 24 22 ), sandwich (e.g., 25 23 ), or tripledecker (e.g., 26 24 ) complexes. The question whether metallabenzynes could also show chemical properties similar to those of benzene or metallabenzenes has been addressed by studying the reactivity of osmabenzynes.…”

Section: Reactivity Of Metallabenzynesmentioning

confidence: 99%

Progress in the Chemistry of Metallabenzynes

Jia

2004

Acc. Chem. Res.

164

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The synthesis and chemical and structural properties of metallabenzynes are reviewed. Reaction of [OsCl2(PPh3)3] with HC⋮CSiMe3 produces the osmabenzyne [Os(⋮CC(SiMe3)C(CH3)C(SiMe3)CH)Cl2(PPh3)2], which undergoes electrophilic substitution reactions with HBF4 and Br2 to give new osmabenzynes. The reactivities and the X-ray diffraction data of osmabenzynes indicate that these metallacycles have aromatic properties. Unlike benzyne, which is thermally unstable, osmabenzynes are thermally much more stable and can be stored for months at room temperature without decomposition. The higher thermal stability of osmabenzynes compared to benzyne can be related to the relatively smaller ring strain and larger conjugation energy.

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“…Subsequent research included substituting one or more CH units of benzene. Initially this involved elements such as N, O, P, and S, but later progress included main group metals (e.g., B, Si, , Ge, and As , ) and even transition metals , (e.g., Nb, , Ta, − Mo, W, Re, Fe, Ru, − Os, , Ni, Pt, and Ir − ). Recently, examples of a 1,4-phosphaboratabenzene and an osmabenzyne − were reported.…”

Section: Introductionmentioning

confidence: 99%

Cycloaddition Reactions of Metalloaromatic Complexes of Iridium and Rhodium: A Mechanistic DFT Investigation

2003

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The mechanistic details of 1,2- and 1,4-cycloaddition reactions of acetone, CO(2), and CS(2) to isostructural iridiabenzene, iridiapyrylium, and iridiathiabenzene complexes, as well as their rhodium analogues, were elucidated by density functional theory (DFT) at the PCM/mPW1K/SDB-cc-pVDZ//mPW1K/SDD level of theory. The calculated reaction profiles concur with reported experimental observations. It was found that the first complex reacts via a concerted reaction mechanism, while the latter two react by a stepwise mechanism. Several factors affecting the reaction mechanisms and outcome were identified. They include the composition and size of the metal-aromatic ring, the length of the substrate C=X (X = O, S) bond, the geometry of the product, the symmetry of the frontier molecular orbitals, and the type of reaction mechanism involved.

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The First Homoleptic Metallabenzene Sandwich Complex

Cited by 5 publications

References 0 publications

Metallabenzenes

Metallabenzenes

Progress in the Chemistry of Metallabenzynes

Cycloaddition Reactions of Metalloaromatic Complexes of Iridium and Rhodium: A Mechanistic DFT Investigation

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