Kinetic investigation of halide substitution in the 17-electron MoCpX2(PMe3)2 system

Poli, Rinaldo; Owens, Beth E.; Linck, R. G.

doi:10.1021/ic00030a026

Cited by 29 publications

(16 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All observable trends for the reversible (Mo II /Mo III couple) potentials are as expected. All potentials are shifted with respect to the corresponding Cp complex by about À 0.2 V. Analogous shifts were previously reported for other complexes, for example, [Cp/Cp*Mo(PMe 3 ) 2 I 2 ] 0/ (À 0.19 V), [Cp/Cp*Mo(PMe 3 ) 2 Cl 2 ] 0/ (À 0.32 V), [40,41] [Cp/Cp*MoCl(PMe 3 ) 3 ] 0/ (À 0.14 V), [39] and [Cp/Cp*Cr(NO)(PPh 3 )I] 0/ (À 0.30 V). [42] The substitution of both Cl ligands by Me groups causes a negative shift of about 0.9 V, while a much smaller but significant negative shift is also induced by the additional methyl group on the diene [37] .…”

Section: Resultssupporting

confidence: 82%

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

Grognec¹,

Poli²

2001

Chem. Eur. J.

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Resultssupporting

confidence: 82%

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

Grognec¹,

Poli²

2001

Chem. Eur. J.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In our laboratory, we have investigated in detail reactivity and redox properties as a function of the ligands for a class of mononuclear complexes of formula CpMoX2L2 where X is a halide ligand and L is typically a tertiary phosphine. [11][12][13][14][15][16][17][18] These are stable paramagnetic compounds characterized by a 17-electron configuration and sharp room temperature isotropic EPR resonances. We extend in this contribution the above class to thiolate and thioether derivatives.…”

Section: Introductionmentioning

confidence: 99%

Half-sandwich molybdenum compounds with phosphine–alkylthiolate and phosphine–thioether ligands. Crystal structure of [CpMo(SCH2CH2PPh2)2][BPh4]

Morales¹,

Poli²,

Richard³

et al. 1999

J. Chem. Soc., Dalton Trans.

Self Cite

View full text Add to dashboard Cite

The reaction of CpMoCl2 with Ph2PCH2CH2SR (R = H, CH3) yields the corresponding addition products CpMoCl2(Ph2PCH2CH2SR), but only the derivative with R = CH3 (compound 5) is sufficiently stable to be isolated as a crystalline solid. The derivative with R = H evolves rapidly to afford a mixture of compounds [CpMo(SCH2CH2PPh2)2] + Cl -, 1, and [CpMoCl(SCH2CH2-PPh2)]2, 2, the former being favored by a larger ligand/Mo ratio. Compound 1 undergoes metathesis with NaBPh4 to afford [CpMo(SCH2CH2PPh2)2] + BPh4 -, 3, which has been characterized by X-ray crystallography. The reaction of CpMoCl2 with 2 equiv of Ph2PCH2CH2S -Li + affords the paramagnetic complex CpMo(SCH2CH2PPh2)2, 4, which is readily oxidized by Cp2Fe 1 or by H + to the corresponding cation. The salts 1 and 3, in turn, may be reduced by Na amalgam, MeLi, or Bu t OK to compound 4. The reversible redox process interconverting 4 and its cation occurs at E1/2 = -1.23 V relative to the ferrocene standard, while compound 5 shows a reversible oxidation process at E1/2 = 0.12 V by cyclic voltammetry. The comparison between these potentials and that previously reported for CpMoCl2(dppe) indicates relative donor abilities in the order Ph2P > MeS and RS -> Cl -. Compound 5 can also be synthesized by Na amalgam or Zn reduction of CpMoCl4(Ph2PCH2CH2SCH3) 6, which is obtained by addition of the ligand to CpMoCl4.

show abstract

“…13,34,42,43 The corresponding dibromide and diiodide derivatives were subsequently obtained by relatively facile halide metathesis processes. 34,44 The use of sodium salts in THF favored the quantitative conversion of the dichloro to the diiodo species, while soluble salts in dichloromethane strongly favored the opposite process. The exchange of the phosphine ligand is an even more facile reaction and proceeds by a dissociative mechanism.…”

Section: Methodsmentioning

confidence: 99%

Different Approaches to Mid-Valent, Paramagnetic Half-Sandwich Complexes of the Heavier Group 6 Metals

Poli¹

1999

Synlett

Self Cite

View full text Add to dashboard Cite

show abstract

Kinetic investigation of halide substitution in the 17-electron MoCpX2(PMe3)2 system

Cited by 29 publications

References 3 publications

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

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

Half-sandwich molybdenum compounds with phosphine–alkylthiolate and phosphine–thioether ligands. Crystal structure of [CpMo(SCH2CH2PPh2)2][BPh4]

Different Approaches to Mid-Valent, Paramagnetic Half-Sandwich Complexes of the Heavier Group 6 Metals

Contact Info

Product

Resources

About