Dications of 3-Phenylindenylidenefluorenes:  Evaluation of Antiaromaticity of Indenyl and Fluorenyl Cations by Magnetic Measures

The series of molybdenum indenyl compounds [(Ind 0 )Mo(CO) 2 (NCMe) 2 ] [BF 4 ] was prepared, and their reactivity toward spiro[2.4]hepta-4,6-diene was studied. It was observed that the spiro-[2.4]hepta-4,6-diene ring opening could be blocked through substitution in the indenyl ring. Hence, the 2-substituted compound [(η 5 -C 9 H 6 Me)Mo(CO) 2 (NCMe) 2 ][BF 4 ] and 1,3-disubstituted compound [(η 5 -C 9 H 5 t Bu 2 )Mo(CO) 2 (NCMe) 2 ][BF 4 ] do not produce the usual ansa-compounds but the compounds with η 4 -bonded spiro[2.4]hepta-4,6-diene [(Ind 0 )(η 4 -C 5 H 4 (CH 2 ) 2 )Mo(CO) 2 ][BF 4 ]. The use of 1-substituted compounds [(η 5 -C 9 H 6 R)Mo(CO) 2 (NCMe) 2 ][BF 4 ] (R = Ph, t Bu) or compounds with less sterically demanding substituents in the 1,3-positions [(η 5 -C 9 H 5 Ph 2 )Mo(CO) 2 (NCMe) 2 ]-[BF 4 ] does not block the ring-opening reaction. These compounds give ansa-molybdenocenes [(Ind 0 )(η 5 -C 5 H 4 CH 2 -η 1 -CH 2 )Mo(CO)][BF 4 ] in a manner similar to that for the unsubstituted analogue. The reaction products were characterized by NMR and IR spectroscopy. Structures of [(η 5 -C 9 H 5 Ph 2 )Mo(η 3 -C 3 H 5 )(CO) 2 ], [(η 5 -C 9 H 6 Ph)(η 5 -C 5 H 4 CH 2 -η 1 -CH 2 )Mo(CO)][BF 4 ], and [(η 5 -C 9 H 5 Ph 2 )(η 5 -C 5 H 4 CH 2 -η 1 -CH 2 )Mo(CO)][BF 4 ] were determined by single-crystal X-ray analysis.

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“…Use of this route is limited by very low yields (∼ 3%). Other substituted indenes were prepared according to literature procedures. − …”

Section: Resultsmentioning

confidence: 99%

Reaction of Spiro[2.4]hepta-4,6-diene with Molybdenum(II) Indenyl Compounds: Effects of Substitution in the Indenyl Ligand

et al. 2011

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“…There has been some debate in the literature whether the fluorenyl cation 1 with a formal 4p electron five-membered ring system in its core should be regarded as a prototypical antiaromatic cation, or if the two annelated benzene rings compensate the antiaromaticity, and the molecule is nonaromatic at best or even aromatic. [1][2][3][4][5][6] In 1980, Olah and Schleyer et al described unsuccessful attempts to isolate 1 in superacidic media: "We were not able to generate the parent 9-fluorenyl cation 1-H by slowly adding SO 2 or SO 2 ClF solutions of possible precursors… at À120 8C. The resulting solutions immediately became dark and unidentifiable polymeric materials were formed".…”

mentioning

confidence: 99%

The Fluorenyl Cation

et al. 2015

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The fluorenyl cation is a textbook example for a 4π antiaromatic cation. However, contrasting results have been published on how the annelated benzene rings compensate the destabilizing effect of the 4π antiaromatic five-membered ring in its core. Whereas previous attempts to synthesize this cation in superacidic media resulted in undefined polymeric material only, we herein report that it can be generated and isolated in amorphous water ice at temperatures below 30 K by photolysis of diazofluorene. Under these conditions, the fluorenylidene is protonated by water to give the fluorenyl cation, which could be characterized spectroscopically. Its absorption in the visible-light range matches that previously obtained by ultrafast absorption spectroscopy, and furthermore, its IR spectrum could be recorded. The IR bands in amorphous ice very nicely match predictions from DFT and DFT/MM calculations, suggesting the absence of strong interactions between the cation and surrounding water molecules.

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“…Dications (73), with various Ar, were prepared to examine the response of the indenyl and fluorenyl cationic portions to magnetic measures of antiaromaticity. 143 All measures supported antiaromaticity, with the indenyl ring system (even in the absence of the aryl substituent) being less aromatic than the fluorenyl ring system. This stands in contrast to the situation with the isolated monocations.…”

Section: Dicationsmentioning

confidence: 94%

Carbocations

McClelland¹

2010

Organic Reaction Mechanisms Series

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Dications of 3-Phenylindenylidenefluorenes: Evaluation of Antiaromaticity of Indenyl and Fluorenyl Cations by Magnetic Measures

Cited by 18 publications

References 25 publications

Reaction of Spiro[2.4]hepta-4,6-diene with Molybdenum(II) Indenyl Compounds: Effects of Substitution in the Indenyl Ligand

Reaction of Spiro[2.4]hepta-4,6-diene with Molybdenum(II) Indenyl Compounds: Effects of Substitution in the Indenyl Ligand

The Fluorenyl Cation

Carbocations

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