Interaction of half-sandwich alkylmolybdenum(III) complexes with B(C6F5)3. The X-ray structure of [CpMo(η4-C4H6)(μ-Cl)(μ-CH2)(O)MoCp][CH3B(C6F5)3]

Grognec, Erwan Le; Poli, Rinaldo; Richard, Philippe; Llusar, Rosa; Uriel, Santiago

doi:10.1016/s0022-328x(01)01196-2

Cited by 4 publications

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“…[37] We can therefore propose that the adduct between the Mo III complex and the MAO activator, {[M]´´´CH 3´´´M AO}, displays a greater resistance toward ion separation with respect to the Nb analogue. Preliminary studies of the interaction between [CpMo(h 4 -C 4 H 6 )(CH 3 ) 2 ] and B(C 6 F 5 ) 3 , which will be reported in a separate contribution, [54] fully confirm this hypothesis. It may also be argued that the MAO reagent could attack the butadiene ligand rather than one of the MoÀX bonds (X Cl or CH 3 ), [30,31,55] given that the addition of Lewis acids to butadiene ligands is documented in the literature.…”

Section: Computational Studiesmentioning

confidence: 61%

“…The interaction between the dialkyl complexes and B(C 6 F 5 ) 3 , however, eventually leads to the identification of a methyl abstraction product, which forms only with difficulty. [54] Under the continued assumption that the activation step involves methyl abstraction by MAO we have investigated theoretically the heterolytic MÀCH 3 bond strengths for complexes [CpMo(h 4 -C 4 H 6 )(CH 3 ) 2 ] (M Mo, Nb; see Scheme 1). Marks and Fragala Á have shown the importance of the metal ± alkyl bond strengths in the thermodynamic cycle which regulates the catalyst activation step.…”

Section: Computational Studiesmentioning

confidence: 99%

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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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