Titanium Complexes with a Linked Amido−Cyclopentadienyl Ligand and a Bidentate Organyl Group: Synthesis, Structure, and Ethene Polymerization Activity

Eberle, Thomas S.; Spaniol, Thomas P.; Okuda, Jun

doi:10.1002/(sici)1099-0682(199802)1998:2<237::aid-ejic237>3.0.co;2-p

Cited by 40 publications

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“…Complexes 134-136 are thermally stable in C 6 D 6 after 24 h at 120°C but extremely oxygen and moisture sensitive and insoluble in aliphatic, but readily soluble in aromatic and polar, solvents, with the greater solubility for the systems containing the larger branched aryl ligands. Similarly, compounds 137-141 were synthesized 167 with the aim to study the influence of varying the R in the linked amido-cyclopentadienyl ligand on olefin polymerization performance. It was realized that due to steric reasons during coordination of the bidentate ligand to the titanium center, the size of R is critically important not only in catalysis but also in determining the yield of Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NR)Cl 2 (137-141) (Chart 9).…”

Section: Mono-cp(ind) Titanium Complexesmentioning

confidence: 99%

Synthesis, Structures, and Catalytic Reactions of Ring-Substituted Titanium(IV) Complexes

et al. 2003

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Section: Mono-cp(ind) Titanium Complexesmentioning

confidence: 99%

Synthesis, Structures, and Catalytic Reactions of Ring-Substituted Titanium(IV) Complexes

et al. 2003

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A New Type of Doubly Silylamido-Bridged Cyclopentadienyl Group 4 Metal Complexes

et al. 2001

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Dedicated to Professor Rafael UsoÂn on the occasion of his 75th birthdayThe isolation of metal complexes containing the h 1 -amidosilyl-h 5 -cyclopentadienyl ligand, which provides more acidic metal centers with a more open coordination site than the ansa-dicyclopentadienyl compounds, has proved particularly useful. [1] These structural features are responsible for their catalytic ability to copolymerize long-chain a-olefins. [2] Numerous contributions in this field have benefited from the research into the use of variously substituted ligands, [3] the characterization of the active cationic species, [4] the development of new industrial applications, [5] and the reactivity of the metal-coordinated amidosilyl moiety. [6] Few examples of doubly bridged h 5 -cyclopentadienyl-di(h 1ligand) metal compounds have been reported. [7] We have now extended our studies in this field by synthesizing new substituted cyclopentadienyl ligands that can form more than one amidosilyl bridge, that is di(h-amidosilyl)-h 5 -cyclopentadienyl ligands, and characterizing and studying the reactivity of their Group 4 metal complexes.The di(amidosilyl)cyclopentadiene C 5 H 4 [SiMe 2 (NHtBu)] 2 (1) was synthesized as a yellow oil from 1,1-(SiMe 2 Cl) 2 C 5 H 4 [8] and LiNHtBu in 12 h at room temperature using THF as solvent. Selective deprotonation of the more acidic cyclopentadiene proton and only one of the amino protons of 1 by using [Zr(NMe 2 ) 4 ] afforded the monosilylamido derivative 2 as a light-brown oil (Scheme 1). A C 6 D 6 solution of 2 was heated to 110 8C to give the disilylamido compound 3 with evolution of NHMe 2 . However this reaction was reversed when the mixture was cooled to room temperature, preventing the isolation of 3. Similar deprotonation of 1 by using the tetrabenzyl compound [Zr(CH 2 Ph) 4 ], gave a mixture of the brown monosilylamido 4, identified by 1 H NMR spectroscopy, and the disilylamido derivative 5 at room temperature (Scheme 1), while 5 was the unique reaction product at Scheme 1. Synthesis of neutral bridged h 5 -cyclopentadienyl mono-and di(h-amidosilyl)titanium and -zirconium complexes and their cationic species.temperatures higher than 65 8C. The deprotonating capacity of complex 5 facilitated the irreversible transformation of 2 into 3 by elimination of the NHMe 2 resulting from that transformation. A similar reaction of 1 with [Ti(CH 2 Ph) 4 ] gave the monosilylamido complex 6 as a red solid, which could only be transformed into the disilylamido derivative 7 by refluxing a solution of the compound in toluene.All the new compounds were characterized by elemental analyses, and the 1 H and 13 C NMR spectra were consistent (see Supporting Information) with the asymmetry of the monosilylamido compounds 2, 4, and 6, and with the presence of a plane of symmetry in the disilylamido compounds 3, 5, and 7 (Scheme 1). The chemical shifts of the tBu tertiary carbon atoms were observed between d 55.8 (3) and d 61.5 (6) for bridged, and between d 49.6 (2) and d 49.8 (6) for unbridged amidosilyl groups; t...

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Diene-Containing Half-Sandwich MoIII Complexes as Ethylene Polymerization Catalysts: Experimental and Theoretical Studies

Grognec¹,

Poli²

2001

Chem. Eur. J.

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Seventeen-electron compounds of MoIII having the general formula [(eta5-C5R5)Mo(eta4-diene)X2] (R = H, Me: dieney = butadiene, isoprene, or 2,3-dimethylbutadiene: X= Cl, CH3) are a new class of ethylene polymerization catalysts. The polyethylene obtained shows a bimodal distribution, the major weight fraction being characterized by very long (M around 10(6)) and highly linear polymer chains. The newly prepared pentamethylcyclopentadienyl (Cp*) derivatives are more active than the cyclopentadienyl (Cp) derivatives, but much less active than previously investigated niobiumIII compounds having the same stoichiometry. On the other hand, the turnover frequency of the active site leading to the high molecular weight chains is at least 10 times greater than that obtained with the corresponding Nb catalyst. The reason for the low activity is explained by a difficult activation process that is attributed to the low polarity and high strength of the Mo-alkyl bond. This is confirmed by a Mulliken charge analysis of density functional theory (DFT) geometry-optimized [CpM(eta4-C4H6)(CH3)2] (M = Nb, Mo) and by the calculation of the heterolytic bond dissociation energies. DFT calculations have also been carried out on the ethylene insertion coordinate for the [CpM(eta4-C4H6)(CH3)]+ model of the presumed active site. The results indicate an equivalent activation barrier to insertion for the Nb and Mo systems. Differences in optimized geometries for the reaction intermediates are attributed to the presence of the extra electron for the Mo system. This electron opposes the formation of M-H-C agostic interactions, while it strengthens the back-bonding M-ethylene interaction, but otherwise plays no active role in the polymer chain propagation mechanism. According to the calculations, the chain propagation for the Mo system occurs entirely on the spin doublet surface, the minimum energy crossover point with the quartet surface lying at a higher energy than the transition state for insertion on the doublet surface.

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Titanium Complexes with a Linked Amido−Cyclopentadienyl Ligand and a Bidentate Organyl Group: Synthesis, Structure, and Ethene Polymerization Activity

Cited by 40 publications

References 35 publications

Synthesis, Structures, and Catalytic Reactions of Ring-Substituted Titanium(IV) Complexes

Synthesis, Structures, and Catalytic Reactions of Ring-Substituted Titanium(IV) Complexes

A New Type of Doubly Silylamido-Bridged Cyclopentadienyl Group 4 Metal Complexes

Diene-Containing Half-Sandwich MoIII Complexes as Ethylene Polymerization Catalysts: Experimental and Theoretical Studies

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