<i>ansa</i>-Metallocene imide niobium compounds

Chernega, Alexander N.; Green, Malcolm L. H.; Suárez, Alehandra G.

doi:10.1139/v95-142

Cited by 16 publications

(3 citation statements)

References 12 publications

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“…showed that the ipso-carbon was α to the bridgehead, 25 and so it seems likely that a similar situation holds here. The data do not allow identification of the relative stereochemistries of the two stereocentres.…”

Section: Resultssupporting

confidence: 56%

Hydrazido(2−) complexes of niobocene

Green¹,

James²,

Chernega³

1997

J. Chem. Soc., Dalton Trans.

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Section: Resultssupporting

confidence: 56%

Hydrazido(2−) complexes of niobocene

Green¹,

James²,

Chernega³

1997

J. Chem. Soc., Dalton Trans.

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“…The structure shows the Me 2 Si(C 5 H 4 ) 2 ansa ligand chelating the niobium center and is the first to be determined of a group 5 ansa complex where both cyclopentadienyl rings of the ansa ligand are bound to the metal in an η 5 -mode only as opposed to the previously reported structures of ansa -niobocene complexes where the cyclopentadienyl rings also exhibit σ bonding to the metal. , The cent(1)−Nb−cent(2) angle of 130.0(5)° (cent(1) is the centroid of C(41)−C(45), and cent(2) is the centroid of C(51)−C(55)) is slightly greater than that observed for (η 5 -C 5 H 4 SiMe 3 ) 2 NbCl(PhC⋮CPh) (cent(1)−Nb−cent(2) angle of 128.4°) . This indicates that bridging the cyclopentadienyl rings of the ansa ligand does not greatly affect their disposition with respect to the metal center.…”

mentioning

confidence: 85%

ansa-Niobocene Complexes: Synthesis and Characterization of Novel Complexes [Me₂Si(η⁵-C₅H₄)₂]NbCl₂and [Me₂Si(η⁵-C₅H₄)₂]NbCl(RC⋮CR) (R = Me, Ph). X-ray Crystal Structure of [Me₂Si(η⁵-C₅H₄)₂]NbCl(MeC⋮CMe)

et al. 1996

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The ansa-niobocene(IV) dichloride complex [Me2Si(η5-C5H4)2]NbCl2 (1) has been prepared by the reaction of NbCl4(THF)2 and [Me2Si(C5H4)2]Tl2 in THF. The reduction of 1 by sodium amalgam in the presence of an alkyne (2-butyne or diphenylacetylene) yielded the ansa-niobocene(III) monochloride alkyne complexes [Me2Si(η5-C5H4)2]NbCl(RC⋮CR) (R = Me (2), Ph (3)). Compounds 1−3 were characterized by IR, ESR, and NMR spectroscopy. In addition, the structure of 2 was determined by single-crystal X-ray diffraction.

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“…Reports of group 5 ansa- metallocenes are limited and generally restricted to C 2 v - symmetric metallocene frameworks, ,17a,b,− except for one report of C 1 - symmetric ansa- niobocene imido complexes 17c. In this report we describe the synthesis and characterization of a series of low-symmetry, singly and doubly [SiMe 2 ]-bridged group 5 metallocene olefin hydride complexes.…”

Section: Introductionmentioning

confidence: 95%

Preparation of ansa-Niobocene and ansa-Tantalocene Olefin Hydride Complexes as Transition State Analogues in Metallocene-Catalyzed Olefin Polymerization

et al. 2002

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To examine the effects of cyclopentadienyl and olefin substitution on preferred stereochemistry, a series of singly [SiMe 2 ]-bridged ansa-niobocene and -tantalocene olefin hydride complexes has been prepared via reduction and alkylation of the corresponding dichloride complexes. In this manner, [Me 2 Si(η 5 -C 5 H 4 )(η 5 -C 5 H 3 -32 )]Ta(CH 2 dCHR′)H (R′ ) H, C 6 H 5 ) have been prepared and characterized by NMR spectroscopy and, in some cases, X-ray diffraction. The doubly [SiMe 2 ]-bridged ansatantalocene ethylene hydride complex [(1,2-SiMe 2 ) 2 (η 5 -C 5 H-3,5-(CHMe 2 ) 2 )(η 5 -C 5 H 2 -4-CMe 3 )]-Ta(CH 2 dCH 2 )H has been prepared from thermolysis of the methylidene methyl complex [(1,2-SiMe 2 ) 2 (η 5 -C 5 H-3,5-(CHMe 2 ) 2 )(η 5 -C 5 H 2 -4-CMe 3 )]Ta(CH 2 )CH 3 . Addition of an excess of propylene or styrene to the tantalocene ethylene hydride results in olefin exchange and formation of the olefin hydride complexes [(1,2-SiMe 2 ) 2 (η 5 -C 5 H-3,5-(CHMe 2 ) 2 )(η 5 -C 5 H 2 -4-CMe 3 )]Ta(CH 2 dCHR′)H (R′ ) CH 3 , C 6 H 5 ). These compounds serve as stable transition state analogues for the much more kinetically labile group 4 metallocenium cationic intermediates in metallocene-catalyzed olefin polymerization. Characterization of the thermodynamically preferred isomers of metallocene olefin hydride complexes reveals that alkyl substitution on the cyclopentadienyl ligand array may have a significant effect on the stereochemistry of olefin coordination.

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ansa-Metallocene imide niobium compounds

Cited by 16 publications

References 12 publications

Hydrazido(2−) complexes of niobocene

Hydrazido(2−) complexes of niobocene

ansa-Niobocene Complexes: Synthesis and Characterization of Novel Complexes [Me₂Si(η⁵-C₅H₄)₂]NbCl₂and [Me₂Si(η⁵-C₅H₄)₂]NbCl(RC⋮CR) (R = Me, Ph). X-ray Crystal Structure of [Me₂Si(η⁵-C₅H₄)₂]NbCl(MeC⋮CMe)

Preparation of ansa-Niobocene and ansa-Tantalocene Olefin Hydride Complexes as Transition State Analogues in Metallocene-Catalyzed Olefin Polymerization

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ansa-Metallocene imide niobium compounds

Cited by 16 publications

References 12 publications

Hydrazido(2−) complexes of niobocene

Hydrazido(2−) complexes of niobocene

ansa-Niobocene Complexes: Synthesis and Characterization of Novel Complexes [Me2Si(η5-C5H4)2]NbCl2and [Me2Si(η5-C5H4)2]NbCl(RC⋮CR) (R = Me, Ph). X-ray Crystal Structure of [Me2Si(η5-C5H4)2]NbCl(MeC⋮CMe)

Preparation of ansa-Niobocene and ansa-Tantalocene Olefin Hydride Complexes as Transition State Analogues in Metallocene-Catalyzed Olefin Polymerization

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ansa-Niobocene Complexes: Synthesis and Characterization of Novel Complexes [Me₂Si(η⁵-C₅H₄)₂]NbCl₂and [Me₂Si(η⁵-C₅H₄)₂]NbCl(RC⋮CR) (R = Me, Ph). X-ray Crystal Structure of [Me₂Si(η⁵-C₅H₄)₂]NbCl(MeC⋮CMe)