Reaction of diene Group 4 metallocene complexes with metal carbonyls: a novel entry to Fischer-type carbene complexes

Erker, Gerhard; Dorf, Ulrich; Benn, Reinhard; Reinhardt, Rolf Dieter; Petersen, Jeffrey L.

doi:10.1021/ja00336a071

Cited by 72 publications

(17 citation statements)

References 1 publication

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“…More broadly, the observation of oxidative cyclization with pyridine(diimine) ruthenium complexes where the chelate is redox innocent supports that access to triplet structures in so-called “two-state” reactivity is not a requirement for this C–C bond forming step. These results are consistent with other previously reported oxidative cyclizations with zirconium, − , nickel, − and platinum, in where the redox events are confined to the metal and the reaction proceeds exclusively on the S = 0 surface. Taken together, these oxidative cyclization studies pinpoint that the differentiating step facilitated by [(PDI)Fe] complexes in the intermolecular [2 + 2] cyclization event is the facile C(sp 3 )–C(sp 3 ) reductive elimination.…”

Section: Results and Discussionsupporting

confidence: 93%

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

et al. 2021

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Aryl-substituted pyridine(diimine) iron complexes promote the catalytic [2 + 2] cycloadditions of alkenes and dienes to form vinylcyclobutanes as well as the oligomerization of butadiene to generate divinyl(oligocyclobutane), a microstructure of poly(butadiene) that is chemically recyclable. A systematic study on a series of iron butadiene complexes as well as their ruthenium congeners has provided insights into the essential features of the catalyst that promotes these cycloaddition reactions. Structural and computational studies on iron butadiene complexes identified that the structural rigidity of the tridentate pincer enables rare s-trans diene coordination. This geometry, in turn, promotes dissociation of one of the alkene arms of the diene, opening a coordination site for the incoming substrate to engage in oxidative cyclization. Studies on ruthenium congeners established that this step occurs without redox involvement of the pyridine(diimine) chelate. Cyclobutane formation occurs from a metallacyclic intermediate by reversible C(sp3)–C(sp3) reductive coupling. A series of labeling experiments with pyridine(diimine) iron and ruthenium complexes support the favorability of accessing the +3 oxidation state to trigger C(sp3)–C(sp3) reductive elimination, involving spin crossover from S = 0 to S = 1. The high density of states of iron and the redox-active pyridine(diimine) ligand facilitate this reactivity under thermal conditions. For the ruthenium congener, the pyridine(diimine) remains redox innocent and irradiation with blue light was required to promote the analogous reactivity. These structure–activity relationships highlight important design principles for the development of next generation catalysts for these cycloaddition reactions as well as the promotion of chemical recycling of cycloaddition polymers.

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Section: Results and Discussionsupporting

confidence: 93%

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

et al. 2021

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“…31, [67][68][69] For complex 5, narrow signals are also observed in both 1 H and 13 C NMR. The 1 H NMR in THF-d 8 of complex 5 shows the same magnetic environment as observed in complex 4, creating a signal for each SiMe 2 group and each t Bu group, as well as only three signals for the allylic hydrogens for both ligands.…”

Section: Synthesis Of Complexes 4 Andmentioning

confidence: 89%

Synthesis, Characterization, and Catalytic Activities for the Polymerization of Olefins Promoted by Zirconium(III) and Titanium(III) Allyl Complexes

et al. 2001

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The reaction of early-transition-metal halides MCl 4 (M ) Zr, Ti) with 2 equiv of the lithium allyl compound ( t BuMe 2 SiCH) 2 CHLi‚TMEDA in toluene produced the corresponding reduced complexes [{( t BuMe 2 SiCH) 2 CH} 2 M(µ-Cl) 2 Li‚TMEDA] (M ) Zr (1), Ti (2)), that were isolated as air-sensitive dark brown (Zr) and brick red (Ti) crystals in 48% and 42% yield, respectively. In addition, each reaction is associated with the formation of the dimer of the allyl ligand (3). Complexes 1 and 2 and dimer 3 were fully characterized spectroscopically, including solid-state X-ray diffraction studies. Complex 1 represents the first solid-state characterization for a Zr(III)-allyl complex. Oxidation of complexes 1 and 2 allows the formation of the corresponding neutral complexes {( t BuMe 2 SiCH) 2 CH} 2 MCl 2 (M ) Zr (4), Ti 5)), which were isolated as air-sensitive light yellow (Zr) and orange (Ti) powders in 23% and 11% yields, respectively. The allylic moieties in complex 5 showed a dynamic interconverting coordination from η 3 to η 1 , causing an alternation between C 2 and C 2v symmetries of the complex. For the cationic complex 4 a similar dynamic interconverting coordination from η 3 to η 1 was observed. The catalytic activities of complexes 1 and 2 activated with MAO in the polymerization of propylene and ethylene were studied. The activity of complexes 1 and 2 was compared to the corresponding activities presented by complexes 4 and 5, respectively, indicating that during the polymerization process, Zr(III) and Ti(III) are oxidized to the corresponding cationic Zr(IV) and Ti(IV) species. For propylene, an elastomeric polypropylene was obtained, whereas for ethylene high-density polyethylene was produced. When the η 3 coordination modes of the ligands are operative in the complex, a cationic racemic octahedral compound is formed, which is responsible for the polymerization of the isotactic domains, whereas when the η 1 coordination modes of the ligands are effective, a cationic tetrahedral complex is obtained, accounting for the atactic domains. The formations of isotactic-atactic domains within a polymer chain give rise to elastomeric polypropylene.

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“…For the parent zirconocene complex, both h 3 and h 1 allyl haptomers have been suggested. 26, 27 Variabletemperature NMR experiments were conducted in toluene-d 8 to further explore the dynamic of the allyl ligand. Representative spectra are reported in the ESI.…”

Section: Resultsmentioning

confidence: 99%

Cyclisation of α,ω-dienes promoted by bis(indenyl)zirconium sandwich and ansa-titanocene dinitrogen complexes

et al. 2011

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Metallation of a variety of α,ω-dienes has been explored with an η(9),η(5)-bis(indenyl)zirconium sandwich compound and an ansa-titanocene dinitrogen complex. The η(9),η(5)-bis(indenyl)zirconium sandwich compound, (η(9)-C(9)H(5)-1,3-Pr(2))(η(5)-C(9)H(5)-1,3-(i)Pr(2))Zr, served as an isolable source of Negishi's reagent and readily formed a kinetic mixture of cis and trans diastereomers of the corresponding zirconacyclopentanes upon diene metallation. For pure hydrocarbon substrates such as 1,6-heptadiene and 1,7-octadiene, an equimolar amount of cis and trans diastereomers were the kinetic products; isomerization to the thermodynamically favoured trans isomers was observed over time at ambient temperature or upon heating to 105 °C, respectively. By contrast, substitution of the methylene or ethylene spacer in the α, ω-diene with a fluorenyl group (e.g. 9,9-diallylfluorene) resulted in exclusive kinetic formation of the trans diastereomer. Amino-substituted dienes were also readily cyclised and one example was characterised by single-crystal X-ray diffraction. Similar studies were also conducted with the ansa-titanocene dinitrogen complex, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Ti](2)(μ(2),η(1),η(1)-N(2)), and both kinetic and thermodynamic selectivities evaluated. The use of a C(1) symmetric ansa-metallocene increases the number of isomeric possibilities. For diallyl tert-butyl amine, diene metallation was more selective than for the bis(indenyl)zirconium sandwich compound and isomerization was also more rapid. Preliminary functionalisation reactivity for both the zircona- and titanocycles was also explored.

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Reaction of diene Group 4 metallocene complexes with metal carbonyls: a novel entry to Fischer-type carbene complexes

Cited by 72 publications

References 1 publication

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

Synthesis, Characterization, and Catalytic Activities for the Polymerization of Olefins Promoted by Zirconium(III) and Titanium(III) Allyl Complexes

Cyclisation of α,ω-dienes promoted by bis(indenyl)zirconium sandwich and ansa-titanocene dinitrogen complexes

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