Instability of 15-electron derivatives. X-ray structure of Cp☆MoCl2(PMe2Ph)2 and [Cp☆MoCl2(PMe2Ph)2]AlCl4

Abugideiri, Fatima; Keogh, D. Webster; Kraatz, Heinz‐Bernhard; Pearson, Wayne H.; Poli, Rinaldo

doi:10.1016/0022-328x(94)00005-w

Cited by 20 publications

(22 citation statements)

References 36 publications

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“…On the other hand, a metal-metal bond is lost. A quantitative reaction occurs for the Cp* precursor with L = PMe 3 or PMe2Ph, whereas no reaction occurs with the bulkier ligands PMePh2 and PPh3, 66 while the analogous precursor with the sterically less demanding Cp ring reacts with all the above ligands. 20 The stability of a Cp* product with Ph2PCH2CH2PPh2, whose steric bulk is similar to that of two PMePh2 ligands, illustrates how delicate this steric balance is.…”

Section: Methodsmentioning

confidence: 99%

“…A similar chlorine abstraction was previously observed when treating [MoCp*Cl2-(PMe2Ph)2] with AlCl3 in CH2Cl2. 66 It was proposed that the abstraction of a chloride ion by AlCl3 produces the highly reactive 15-electron species [MoCp*Cl-(PMe2Ph)2] + , which is capable of abstracting a Cl atom in order to produce the more stable 16-electron species [MoCp*Cl2 (PMe2Ph)2] + . A similar mechanism may therefore take place for the formation of compound 5 (Scheme 2).…”

Section: Methodsmentioning

confidence: 99%

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Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

Camus

Morales

Andrieu

et al. 2000

J. Chem. Soc., Dalton Trans.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

Camus

Morales

Andrieu

et al. 2000

J. Chem. Soc., Dalton Trans.

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“…Given the existence and stability of 15 electron [CpCrCl2(PR3)] with three unpaired electrons, the corresponding molybdenum system may also adopt a spin-quartet ground state and, provided the initial doublet complex can undergo a change of spin somewhere along the phosphine dissociative pathway, this should lead to a low-energy pathway for substitution. Efforts to isolate this unsaturated intermediate or models of it were, however, unfruitful, [8,9] as were also attempts to observe it by spectroscopic methods.…”

Section: Introductory Examplementioning

confidence: 99%

Understanding the reactivity of transition metal complexes involving multiple spin states

Harvey

2003

Coordination Chemistry Reviews

323

220

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In coordination chemistry, many reactions involve several electronic states, in particular states of different spin. This phenomenon of "Multiple-State Reactivity" has been recognized for some time, both for gas-phase reactions of "bare" metal ions, and for transition metal complexes in solution. Until recently, however, much of the discussion of these systems has remained qualitative, because standard computational methods do not allow the location of the critical points for these processes, the Minimum Energy Crossing Points (MECPs) between states of different spin. Increased computational resources and new algorithms now enable MECPs to be located for large, realistic transition-metal containing systems, yielding important new insight into the mechanisms of important reactions such as oxidative addition of C-H bonds to metal centers and ligand association/dissociation processes. Several examples will be presented for inorganic, organometallic and bioinorganic reactions.

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“…Therefore, the pacidic nature of the diene ligand is the major cause forcing electron pairing in the 15- [86,87] the latter having one of the mesityl groups h 6 -bonded to the metal center. Furthermore, species [CpMoCl 2 (PR 3 )], whose isolation did not prove possible, [88] would also adopt a spin quartet ground state according to DFT calculations. [74±76] On the basis of this simple model, we predict that the replacement of the diene with a less p acidic ligand should stabilize the quartet ground state of a putative [CpMoL 2 R] intermediate, possibly leading to more efficient polymerization catalysts.…”

Section: Discussionmentioning

confidence: 99%

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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Instability of 15-electron derivatives. X-ray structure of Cp☆MoCl2(PMe2Ph)2 and [Cp☆MoCl2(PMe2Ph)2]AlCl4

Cited by 20 publications

References 36 publications

Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

Understanding the reactivity of transition metal complexes involving multiple spin states

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

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