No abstract

No abstract

The chemistry of transition metal-containing metallabenzenes has attracted considerable attention.[1] Previous studies have led to the isolation and characterization of a number of stable metallabenzenes, especially those of osmium, [2][3][4] iridium, [5][6][7][8] platinum, [9] ruthenium, [10,11] and rhenium. [12] Many interesting chemical properties of metallabenzenes have also been discovered. For example, it has been demonstrated that metallabenzenes can undergo electrophilic substitution reactions, [2a, 5d] cycloaddition reactions, [8d, 9c] nucleophilic addition reactions, [13] and nucleophilic aromatic substitution of hydrogen. [14] Another common reactivity of metallabenzenes is that they can undergo migratory insertion reactions to give cyclopentadienyl complexes. The transformation has been demonstrated with well-characterized metallabenzenes [2e, 6b,-d,e, 10b] as well as a spectroscopically characterized ruthenabenzene, [15] and it has been proposed as a key step in the formation of cyclopentadienyl complexes.[1]Compounds closely related to metallabenzenes are metallabenzynes.[16] Compared with the chemistry of metallabenzenes, that of metallabenzynes is much less developed, which is partly due to the lack of convenient methods to synthesize such compounds.[17] Structurally, metallabenzynes are similar to metallabenzenes in that both have a delocalized structure. Thus it might be expected that metallabenzynes should have properties similar to those of metallabenzenes. Indeed, previous studies have demonstrated that metallabenzynes, like metallabenzenes, can also undergo electrophilic substitution reactions [18] and nucleophilic addition reactions.[17c] As formation of cyclopentadienyl complexes from metallabenzenes by migratory insertion reactions is well-known, one might expect that metallabenzynes could also undergo migratory insertion reactions to give carbene complexes. However, such reactions have not been previously observed. Herein, we present a reliable method to prepare osmabenzynes along with the first examples of conversion of metallabenzynes into carbene complexes.We recently observed that reaction of zinc with the osmium vinyl carbyne complex [OsCl 3 { C À CH = C(2-ClC 6 H 4 ) 2 }(PPh 3 ) 2 ] produced a osmanaphthalyne complex. [19] The reaction was proposed to proceed through a 16e fourcoordinate square planar osmium carbyne complex, which undergoes an oxidative addition reaction involving a CÀCl bond. Inspired by the observation, we envisioned that reactions of zinc with carbyne complexes of the type [OsCl 3 { C À CH = CR À CR' = CClR''}(PPh 3 ) 2 ] might lead to the formation of new osmabenzynes.To test this hypothesis, we first prepared the meridional osmium carbyne complex 1 and then treated it with zinc in THF at room temperature. An in situ 31 P NMR study showed that osmabenzyne 2 with substituents on the C3 and C5 positions was produced as the major phosphorus-containing product (Scheme 1), which can be isolated in 62 % yield after column chromatography.The osmabenzyne 2 has bee...

Treatment of the osmabenzyne complex Os{C-C(SiMe 3 )C(CH 3 )-C(SiMe 3 )CH−}Cl 2 (PPh 3 ) 2 with Mo-(CO) 6 in refluxing benzene produced the η 5 -chlorocyclopentadienyl complex Os{η 5 -C 5 HCl(CH 3 )(SiMe 3 ) 2 }Cl(CO)(PPh 3 ) and Mo(CO) 5 (PPh 3 ). A computational study suggests that the chlorocyclopentadienyl complex is most likely produced via the carbene intermediate Os{C(C(SiMe 3 )C(CH 3 )-C(SiMe 3 )CH−)}Cl 2 (CO)(PPh 3 ) formed by a migratory insertion reaction of the osmabenzyne complex Os{C-C(SiMe 3 )C(CH 3 )-C(SiMe 3 )CH}Cl 2 (CO)(PPh 3 ). DFT calculations show that the relative thermal stability of metallabenzynes Os(C-CHCHCHCH)Cl 2 (L) 2 and the corresponding isomeric carbene complexes Os{C(−CHCHCHCH−)}Cl 2 (L) 2 as well as the chlorocyclopentadienyl complexes Os(η 5 -C 5 ClH 4 )Cl(L) 2 (L = CO, phosphine, pyridine, amine) is strongly dependent on ligand L.

No abstract

The Mott scattering in the presence of a linearly polarized laser field is investigated in the first Born approximation. The theoretical results indicate that at medium and large scattering angles, a large amount of multiphoton processes take place in the course of scattering. The photoabsorption ͑inverse bremsstrahlung͒ predominates the photoemission ͑bremsstrahlung͒. The sum rule for the multiphoton cross sections is notably violated. When the laser polarization deviates from the incident direction, the laser-modified ͑summed͒ cross section shows a considerable dependence on the azimuthal angle of the scattered electron. The dependencies of the cross section on the field strength, the frequency, the polarization direction, and the electron-impact energy are studied.

Metalla-aromatics are attractive species because they exhibit the properties of both organometallics and aromatics. Reported metal-bridged polycyclic aromatic complexes, as well as Möbius aromatic species, are still rare. Herein, we present the construction of two new metal-bridged polycyclic aromatic frameworks, α-metallapentalenofurans and lactone-fused metallapentalynes, by the reactions of osmapentalyne with terminal aryl alkynes in the presence of H O or HBF /H O, respectively. DFT calculations show that the α-metallapentalenofurans possess rare planar Craig-type Möbius aromaticity derived from the 11-center-12-electron d -p π-conjugation. This study offers a new route for the construction of polycyclic metalla-aromatics as well as planar Möbius aromatic species.

No abstract