ansa-metallocene derivatives

Schwemlein, Heinz; Zsolnai, László; Hüttner, Gottfried; Brintzinger, Hans‐Herbert

doi:10.1016/s0022-328x(00)99205-2

Cited by 43 publications

(34 citation statements)

References 12 publications

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“…As was found in the experimental values, the shortest Co ϩ -ring carbon bond is to the ipso carbon The bridged and unbridged ferrocenes that were measured were derived from 6,6-dimethylfulvene, 6-phenylfulvene and 6,6-diphenylfulvene (unbridged only). For the unbridged tetramethylferrocene (8), the CϪC bonds in the cyclopentadienyl rings range from 1.425 Å to 1.433 Å , and are very similar to those of the bridged tetramethylferrocene 9 (1.426 Å to 1.442 Å ). The difference between these two compounds is found in their Fe-ring carbon bonds (2.048 Å to 2.075 Å , compared to 1.975 Å to 2.087 Å for the bridged structure).…”

Section: Theoretical Calculationsmentioning

confidence: 84%

“…From this, it can be seen that the formation of 11 is energetically more favourable. Further ∆H values were calculated for the breaking of the bridging moiety, to give the unbridged metallocene, namely Ϫ30.2 kcal/mol (8) and Ϫ28.2 kcal/mol (10). These values show that not only does the bridge impose a strain on the metallocene, but the substituents do as well.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

“…[6,7] Many of these compounds contain an ansa-bridge, which restricts the geometry of the rings and therefore changes the electronic properties of the metallocene. [8,9] The rings can be the same, as in bis-cyclopentadienyl, [10,11] bisindenyl, [12] bis-fluorenyl [13] or bis-tetrahydroindenyl [14] systems, but they can also consist of different ligands as in the case of the fluorenyl-cyclopentadienyl metallocene. [15] We wish to report the synthesis and structural characterisation of the trans- [1, 2 C 2 H 2 (η 5 -C 5 H 4 ) 2 ]Co ϩ cation, which was isolated as its PF 6 Ϫ salt 1.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Structural Characterisation of a Novel Chiral ansa-Cobaltocenium Hexafluorophosphate

Fox¹,

Dunne²,

Tacke³

et al. 2002

Eur. J. Inorg. Chem.

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Keywords: Metallocenes / Structural analysis / Density functional calculations / Cobalt (1) was synthesised and its structure derived by X-ray crystallography and spectroscopic methods in conjunction with theoretical calculations. To gain an insight into the effect of these bridging atoms and the exocyclic substituents on the sandwich structure, a study was undertaken in which comparisons were drawn between this ansa-cobaltocenium ion and other previously reported struc-

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Section: Theoretical Calculationsmentioning

confidence: 84%

Section: Theoretical Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesis and Structural Characterisation of a Novel Chiral ansa-Cobaltocenium Hexafluorophosphate

Fox¹,

Dunne²,

Tacke³

et al. 2002

Eur. J. Inorg. Chem.

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“…[5] Unlike [Cr(CO)Cp 2 ], complex 1 is stable in the absence of a CO atmosphere. In fact, the CO ligand is required to stabilize the 16 e ansa-chromocene fragment.…”

Section: }]mentioning

confidence: 99%

Ring‐Borylated 15‐Electron and 17‐Electron ansa‐Chromocene Complexes, their Physical Properties and Molecular Structures

Shapiro

Sinnema

Perrotin

et al. 2007

Chemistry A European J

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A detailed study of the thermal decomposition of the zwitterionic, ring-borylated ansa-chromocene hydrido carbonyl complex [Cr(CO)H{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (2) is described. This complex is formed in the reaction between [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}] (1) and B(C(6)F(5))(3) in toluene at -78 degrees C. Above -25 degrees C, 2 decomposes to a 50:50 mixture of the low-spin, 17e Cr(III) complexes [Cr(CO){Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3b) and [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (4). Carbon monoxide elimination from 3 b generates high-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3a), which coordinates two other electron-donating ligands, such as xylyl isocyanide, PMe3, and PPh(2)Me to form the low-spin, 17 e electron complexes 3c, 3d, and 3e, respectively. High-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (5) is generated by heating 3 b in toluene at 100 degrees C and periodically removing the evolved CO. Efforts to isolate more than a few X-ray quality crystals of 5 were thwarted by its tendency to form an insoluble precipitate (6) with the same molecular formula. Heating the solution of 5 at 120 degrees C results in its partial conversion (ca. 28 %) to 3a, thereby allowing the formation of 3a in yields as high as 74 % from the reaction between 1 and B(C(6)F(5))(3). The X-ray crystal structures of 3 b-e and 5 are described. Cyclic voltammetry measurements on 3 a-e reveal a dramatic reduction in the redox potentials of the complexes relative to their non-borylated analogues. DFT calculations show that this is due primarily to electrostatic stabilization of the oxidized species by the negatively charged borylate group. EPR and 19F NMR spectroscopy allow 3a to be distinguished from its Lewis base adducts 3 b-e and reveal the relative affinities of different Lewis bases for the chromium.

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“…The first ansa-chromocene compound, {Me 4 C 2 (C 5 H 4 ) 2 } CrCO (1) was reported by Schwemlein and Brintzinger in 1983 (Eqn 1) [58]. Unlike the unbridged parent chromocene carbonyl derivative, 1 is stable against CO loss at room temperature.…”

Section: Ansa-chromocene Compounds Two Atom-bridged Ansa-chromocene Cmentioning

confidence: 99%

The Elusive Chemistry of Bent-Sandwich Chromocene

Shapiro¹

2007

COC

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Until recently the chemistry of bent-sandwich chromocene eluded examination due to the propensity of dicyclopentadienylchromium toward cyclopentadienyl ring loss and thermodynamic barriers to coordinating two electron donating ligands such as CO. The use of modified cyclopentadienyl ligands such as acyclic pentadienyl ligands and linked dicyclopentadienyl ligands, by changing the electronic demands of the metal, have allowed access to neutral and cationic bent-sandwich chromocene derivatives with interesting structures, redox properties, and ligand coordination/substitution behavior. This review article provides an overview of the synthesis, magnetic properties, and reactivity of Cp 2 Cr (Cp = C 5 H 5 ) and related compounds, the chemistry of open chromocene compounds containing acyclic pentadienyl ligands, and a more detailed discussion of the chemistry of ansa-chromocene complexes, which has been the research focus of the author. INTRODUCTIONThe chemistry of dicyclopentadienylchromium (chromocene) [1,2] has been less illustrious than that of metallocenes of other early transition metals from groups 3-6, some of which are recognized for their catalytic activity toward alkene and alkyne polymerization and other synthetically useful reactions while others have served as model systems for fundamentally interesting transition metal mediated reactions [3]. This situation is due to chromocene's preference for a parallel-ring geometry, which allows it to maintain a high spin electronic configuration with a 3 E 2g (e 2g 3 a 1g

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ansa-metallocene derivatives

Cited by 43 publications

References 12 publications

Synthesis and Structural Characterisation of a Novel Chiral ansa-Cobaltocenium Hexafluorophosphate

Synthesis and Structural Characterisation of a Novel Chiral ansa-Cobaltocenium Hexafluorophosphate

Ring‐Borylated 15‐Electron and 17‐Electron ansa‐Chromocene Complexes, their Physical Properties and Molecular Structures

The Elusive Chemistry of Bent-Sandwich Chromocene

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