Synthetic and structural studies on some organic compounds of zirconium

Antiñolo, Antonío; Bristow, Garry S.; Campbell, Graeme K.; Duff, Alan W.; Hitchcock, Peter B.; Kamarudin, Rose A.; Läppert, Michael F.; Norton, R. J.; Sarjudeen, Nigel; Winterborn, Duncan J.W.; Atwood, Jerry L.; Hunter, William E.; Zhang, Hongming

doi:10.1016/s0277-5387(00)80603-8

Cited by 19 publications

(3 citation statements)

References 10 publications

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“…In 1981, Lappert reported that the reduction potential of Cp 2 ZrCl 2 (−1.70 V) is more negative than that of (Cp TMS ) 2 ZrCl 2 (−1.59 V), thereby indicating that the Me 3 Si group has a poor electron-donating ability relative to that of H 45d. These values were revised by Lappert in 1989 [Cp 2 ZrCl 2 (−1.60 V) and (Cp TMS ) 2 ZrCl 2 (−1.56 V)], indicating that the difference is not as great as previously suggested. More recently, Langmaier has studied the electrochemistry of zirconocene complexes with more than one Me 3 Si group and has concluded that this substituent has a negligible effect on the reduction potential,45e reporting that the reduction potentials of [C 5 H 4 (SiMe 3 )] 2 ZrCl 2 , [C 5 H 3 (SiMe 3 ) 2 ] 2 ZrCl 2 , and [C 5 H 2 (SiMe 3 ) 3 ] 2 ZrCl 2 are identical.…”

Section: Resultsmentioning

confidence: 90%

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

et al. 2002

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The electronic influence of unbridged and ansa-bridged ring substituents on a zirconocene center has been studied by means of IR spectroscopic, electrochemical, and computational methods. With respect to IR spectroscopy, the average of the symmetric and asymmetric stretches (nu(CO(av))) of a large series of dicarbonyl complexes (Cp(R))(2)Zr(CO)(2) has been used as a probe of the electronic influence of a cyclopentadienyl ring substituent. For unbridged substituents (Me, Et, Pr(i), Bu(t), SiMe(3)), nu(CO(av)) on a per substituent basis correlates well with Hammett sigma(meta) parameters, thereby indicating that the influence of these substituents is via a simple inductive effect. In contrast, the reduction potentials (E degrees ) of the corresponding dichloride complexes (Cp(R))(2)ZrCl(2) do not correlate well with Hammett sigma(meta) parameters, thereby suggesting that factors other than the substituent inductive effect also influence E degrees. Ansa bridges with single-atom linkers, for example [Me(2)C] and [Me(2)Si], exert a net electron-withdrawing effect, but the effect is diminished upon increasing the length of the bridge. Indeed, with a linker comprising a three-carbon chain, the [CH(2)CH(2)CH(2)] ansa bridge becomes electron-donating. In contrast to the electron-withdrawing effect observed for a single [Me(2)Si] ansa bridge, a pair of vicinal [Me(2)Si] ansa bridges exerts an electron-donating effect relative to that from the single bridge. DFT calculations demonstrate that the electron-withdrawing effect of the [Me(2)C] and [Me(2)Si] ansa-bridges is due to stabilization of the cyclopentadienyl ligand acceptor orbital, which subsequently enhances back-donation from the metal. The calculations also indicate that the electron-donating effect of two vicinal [Me(2)Si] ansa bridges, relative to that of a single bridge, is a result of it enforcing a ligand conformation that reduces back-donation from the metal.

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Section: Resultsmentioning

confidence: 90%

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

et al. 2002

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“…The role of other substituents is much less understood. One example is the trimethylsilyl group, which is also frequently used as a modifying substituent, since both electron-attracting and electron-donating effects have been experimentally observed depending on the property followed. ,− …”

Section: Introductionmentioning

confidence: 99%

Activation of the (Trimethylsilyl)tetramethylcyclopentadienyl Ligand in Zirconocene Complexes

et al. 2003

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Reduction of [ZrCl2{η5-C5Me4(SiMe3)}2] (1) with excess magnesium in tetrahydrofuran affords a mixture of the monomeric zirconocene hydride [ZrH{η1:η5-C5Me4(SiMe2CH2)}{η5-C5Me4(SiMe3)}] (2) and the dimeric, tetranuclear Zr(III)− and Zr(IV)−magnesium hydride complexes 3 and 4, respectively. In the presence of bis(trimethylsilyl)ethyne (btmse), a similar reduction yields the η2-alkyne complex [Zr{η5-C5Me4(SiMe3)}2(η2-btmse)] (5) as the major product and compounds 2−4 as minor impurities. Upon thermolysis under vacuum, 5 undergoes a 2-fold hydrogen transfer from trimethylsilyl groups in the zirconocene intermediate to leaving btmse to afford [Zr{η5:η1-C5Me4(SiMe2CH2)}2] (6) and a mixture of alkenes (E)- and (Z)-Me3SiCHCHSiMe3 (E ≫ Z). Crystal structures of compounds 2 and 4−6 were determined by X-ray crystallography.

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“…1.25 times as strong a donor as is −CH 3 . In contrast to this evidence, however, the reduction potential ( E red 1/2 ) of substituted Cp′ 2 ZrCl 2 compounds increases in the order (SiMe 3 ) 2 < SiMe 3 < H < Me < Et, indicating that −SiMe 3 is functioning as an electron acceptor relative to hydrogen . In other cases, especially when the steric bulk of the −SiMe 3 comes into play, its electronic effect appears to be negligible …”

Section: Resultsmentioning

confidence: 71%

Balancing Adduct Formation and Ligand Coupling with the Bulky Allyl Complexes [1,3-(SiMe₃)₂C₃H₃]₂M (M = Fe, Co, Ni)

2014

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Passage of CO at atmospheric pressure through solutions of A′ 2 M (M = Fe, Co, Ni; A′ = [1,3-(SiMe 3 ) 2 C 3 H 3 ] − ) in hexanes produces the corresponding allyl complexes A′ 2 Fe(CO) 2 , A′Co(CO) 3 , and A′ 2 Ni(CO), respectively.Although the iron and nickel species can be isolated as pure liquids, the cobalt complex is accompanied by the coupling product 1,3,4,6-tetrakis(trimethylsilyl)-1,5-hexadiene. A′Co(CO) 3 was independently prepared from the reaction of Co 2 (CO) 8 , A′Br, and PhCH 2 N(C 2 H 5 ) 3 + Cl − in aqueous base. The IR stretching frequencies of A′ 2 Fe(CO) 2 and A′Co(CO) 3 are lower than those in the unsubstituted analogues, indicating that the trimethylsilated allyl ligand is a better electron donor than the parent version. Density functional theory calculations were performed on various conformations of the complexes, which reproduced the frequency-lowering effect of the trimethylsilyl groups. They also indicate that the thermodynamics of the formation of A′ 2 Ni(CO) and the unknown (C 3 H 5 ) 2 Ni(CO) are similar, suggesting that the thermal stability of the former is of kinetic origin. Oxidative coupling of the allyl ligands in A′ 2 Fe and A′ 2 Co is induced with I 2 ; this is different from the case with A′ 2 Ni, which has previously been shown to produce the mixed allyl halide complex [A′Ni(μ-I) 2 ] 2 .(2) Article pubs.acs.org/Organometallics

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Synthetic and structural studies on some organic compounds of zirconium

Cited by 19 publications

References 10 publications

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

Activation of the (Trimethylsilyl)tetramethylcyclopentadienyl Ligand in Zirconocene Complexes

Balancing Adduct Formation and Ligand Coupling with the Bulky Allyl Complexes [1,3-(SiMe₃)₂C₃H₃]₂M (M = Fe, Co, Ni)

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Synthetic and structural studies on some organic compounds of zirconium

Cited by 19 publications

References 10 publications

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

The Electronic Influence of Ring Substituents and Ansa Bridges in Zirconocene Complexes as Probed by Infrared Spectroscopic, Electrochemical, and Computational Studies

Activation of the (Trimethylsilyl)tetramethylcyclopentadienyl Ligand in Zirconocene Complexes

Balancing Adduct Formation and Ligand Coupling with the Bulky Allyl Complexes [1,3-(SiMe3)2C3H3]2M (M = Fe, Co, Ni)

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Balancing Adduct Formation and Ligand Coupling with the Bulky Allyl Complexes [1,3-(SiMe₃)₂C₃H₃]₂M (M = Fe, Co, Ni)