ansa-Metallocene derivatives

Raaij, Edith U. van; Brintzinger, Hans‐Herbert

doi:10.1016/0022-328x(88)83149-8

Cited by 23 publications

(23 citation statements)

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“…The 1 H NMR spectrum of complex 1 (see Section 4) is in accord with the expected C 2v -symmetry. Its v(CO) frequency of 1876cm-1 (toluene) is intermediate between those of chromocene carbonyl complexes with C 2 H 4 -bridged [10] and permethylated C s rings [13] (Table O. In its EI mass spectrum, the parent peak M+ at m/ e 378 is rather weak; loss of CO gives rise to the base peak [M -CO]+.…”

Section: Formation and Structure Of The Monocarbonyl Me2si(c5me4)2cr(mentioning

confidence: 99%

“…The increased stability of these ring-bridged complexes has been analyzed in terms of complex deformation and metal-ligand bond enthalpies [12]. The Me 4 C 2-bridged chromocene carbonyl resembles (CSHS)2W(CO) also in that it is converted, at elevated CO pressures, to the dicarbonyl complex Me 4 CiC s H 4 )zCr(CO)z with one 1")3-and one 1")s-bound C s ring [13]. Similar effects result when permethylated C s rings make the Cr centre more electron-rich: while the dicarbonyl complex (C s H s )ZCr(CO)2 is stable only under elevated CO pressures [13], its permethyl analogue T\s,T\3-(C s Me)zCr(CO)2 can be isolated by sublimation in vacuo [14].…”

Section: Introductionmentioning

confidence: 99%

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ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

Schaper¹,

Rentzsch²,

Prosenc³

et al. 1997

Journal of Organometallic Chemistry

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The ring-bridged chromocene carbonyl complex Me z Si(C sMe 4)zCr(CO) 1 is obtained by reaction of Me~ Si(C, MC 4)2 Li ~ with CrCl z. THF in the presence of CO. Reaction with CO transforms the monocarbonyl complex 1 to a dicarbonyl complex MezSi(CsMe4)(Cs(endo-3-H)(2-CHz)Me3)Cr(CO)2 2; in this reaction, a hydrogen atom is shifted from one of the cx-CH 3 groups to the adjacent l3-position of a C s ring ligand. The rate of this reaction is first order in complex and CO concentration, with an activation enthalpy of H oF = 51 ± 3 kJ mol-I and an activation entropy of S oF = 136 ± 10 J mol-I K-I. In toluene solution at 50 cC, complex 2 isomerizes to Me2Si(CsMe4)(Cs(exo-3-H)(2-CH2)Me3)Cr(CO)2 3, then to Me2Si(CsMe4)(Cs(exo-I-H)(2-CHz)Me3)Cr(CO)2 4 and further to Me2Si(CsMe4)(Cs(endo-5-HX2-CHz)Me3)Cr(CO)2 5. The kinetics of these isomerizations, which involve hydrogen migrations and ring rotation reactions, indicate monomolecular reactions. Possible reaction paths and transition states are discussed. The structures of complexes 1-5 were determined by lH NMR spectroscopy, those of 1, 2, 4 and 5 also by single-crystal X-ray diffraction.

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Section: Formation and Structure Of The Monocarbonyl Me2si(c5me4)2cr(mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

Schaper¹,

Rentzsch²,

Prosenc³

et al. 1997

Journal of Organometallic Chemistry

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“…Bei CO-Drucken um 100 bar und Temperaturen unter O°C andererseits entsteht im Gleichgewicht mit (C5H5hCr(CO) ein Dicarbonyl-Komplex (C 5 H 5 ) 2Cr(CO) 2 wie wir kürzlich durch IR-Untersuchungen unter erhöhten CO-Drucken zeigen konnten [6]. Die Beobachtung ähnlicher v(CO)-Banden wie im schon länger bekannten Wolframocen-Analogen (1l-C 5 H 5 )(1]5_C 5 H 5 )W(COh [4,7,8] ließ vermuten, daß hier ebenfalls einer der beiden Ringliganden 1]a-koordiniert vorliegt.…”

Section: Introductionunclassified

Mono‐ und Dicarbonyl‐Komplexe des Decamethylchromocens Eine CO‐induzierte η⁵ → η³ ‐ Ringverschiebung

Raaij

Brintzinger

Zsolnai

et al. 1989

Zeitschrift anorg allge chemie

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Decamethylchromocen, (C5(CH3)5)2 Cr, bildet mit CO den 18‐Elektronen‐Komplex (C5(CH3)5)2Cr(CO). Unter höheren CO‐Drucken entsteht der Dicarbonyl‐Komplex (C5(CH3)5)2Cr(CO)2, der auch in Abwesenheit von CO stabil ist. Eine Röntgenstrukturanalyse ergibt, daß diese Verbindung einen η3‐ und einen η5‐koordinierten Ringliganden enthält und damit ebenfalls als 18‐Elektronen‐Teilchen vorliegt.

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“…Cp 2 Cr binds CO reversibly at 22ºC with K = 6.53 atm -1 [21]. At elevated CO pressures a second CO binds to the complex, also reversibly, to form, presumably, the 18e ring slipped species, ( 3 -C 5 H 5 )( 5 -C 5 H 5 )CrCO 2 .…”

Section: Reactivitymentioning

confidence: 96%

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

Abstract: ansa-Metallocene derivatives xv . Reversible coordination of a second CO ligand to (CSHS)2Cr(CO) and its tetramethylethanediyl-bridged analogue. Evidence for an electron-transfer catalysed ringslippage reaction. IR studies at elevated gas pressure. II *

Cited by 23 publications

References 24 publications

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

Mono‐ und Dicarbonyl‐Komplexe des Decamethylchromocens Eine CO‐induzierte η⁵ → η³ ‐ Ringverschiebung

The Elusive Chemistry of Bent-Sandwich Chromocene

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ansa-Metallocene derivatives

Abstract: ansa-Metallocene derivatives xv *. Reversible coordination of a second CO ligand to (CSHS)2Cr(CO) and its tetramethylethanediyl-bridged analogue. Evidence for an electron-transfer catalysed ringslippage reaction. IR studies at elevated gas pressure. II * *

Cited by 23 publications

References 24 publications

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

ansa-metallocene derivatives XXXVI. Dimethylsilyl-bridged permethyl chromocene carbonyl complexes — syntheses, crystal structures and interconversion reactions

Mono‐ und Dicarbonyl‐Komplexe des Decamethylchromocens Eine CO‐induzierte η5 → η3 ‐ Ringverschiebung

The Elusive Chemistry of Bent-Sandwich Chromocene

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Abstract: ansa-Metallocene derivatives xv . Reversible coordination of a second CO ligand to (CSHS)2Cr(CO) and its tetramethylethanediyl-bridged analogue. Evidence for an electron-transfer catalysed ringslippage reaction. IR studies at elevated gas pressure. II *

Mono‐ und Dicarbonyl‐Komplexe des Decamethylchromocens Eine CO‐induzierte η⁵ → η³ ‐ Ringverschiebung