Synthesis and structure of a diiron divinylidene complex formed by oxidative carbon-carbon coupling

Iyer, R. Subramonia; Selegue, John P.

doi:10.1021/ja00237a052

Cited by 98 publications

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“…This chemistry was first noted by Iyer and Selegue following treatment of [Fe{C=C(H)R}(dppe)Cp]BF 4 with iodosobenzene (R = Me) or Cu(OAc) 2 (R = Me, Ph) at room temperature. [109] Crystallisation of the resulting reaction mixture afforded [{Fe(dppe)Cp} 2 {μ-C=C(R) [109] and later ferrocenium [110] ) or anodic oxidation [109] were unsuccessful, although it was ultimately demonstrated that accumulation of alkynyl radical cations by chemical oxidation at low temperatures can lead to more effective C-C coupling. [111] Alkynyl radical coupling to form bis(vinylidene) species generally occurs in competition with the hydrogen-abstraction pathway, and the relative extent of dimerisation versus hydrogen abstraction is subject to thermodynamic and/or kinetic (steric) factors.…”

Section: Cpј]mentioning

confidence: 99%

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Schauer

Low

2011

Eur J Inorg Chem

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Transition-metal σ-alkynyl complexes are valuable functional materials that have found application as sructural units in the assembly of polymetallic arrays and large molecular structures, reagents for the transfer, oligomerisation or functionalisation of alkynes, magnetic or optical materials and putative components for use in a future molecular-based electronics platform. Many σ-alkynyl complexes are redoxactive, undergoing facile oxidation (reduction) at moderate potentials to generate radical cations (anions) in which the

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Section: Cpј]mentioning

confidence: 99%

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Schauer

Low

2011

Eur J Inorg Chem

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“…8 We have recently shown 9 that oxidative dehydrodimerization of the manganese vinylidene complex (Z involves the formally 16-e mononuclear s-phenylethynyl cation 2 and the bis-carbyne dication 4 as the key sequential intermediates (see Scheme 1). A similar scheme was also reported for (Z 5 -C 5 H 4 Me)(dmpe)Mn=C=CHPh.…”

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confidence: 99%

Oxidative dehydrodimerization of manganese vinylidene complexes (η⁵‐C₅R₅)(CO)(L)MnCCHPh (R = Me, L = CO; R = H, L = PPh₃)

Novikova

Peterleitner

Sevumyan

et al. 2002

Applied Organom Chemis

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The oxidative dehydrodimerization of the phenylvinylidene manganese complexes (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CHPh (5: R=Me, L=CO; 6: R=H, L=PPh 3 ) into the corresponding bisvinylidene compounds (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CPhÐCPh=C=Mn(CO)(L)(Z 5 -C 5 R 5 ) (7: R=Me, L=CO; 8: R=H, L=PPh 3 ) was studied by cyclic voltammetry and chemical experiments. It was found that dehydrodimerization of 5 and 6 proceeds via direct C (b) ÐC (b) In this paper we report on the oxidative dehydrodimerization of manganese vinylidene complexes (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CHPh (5: R=Me, L=CO; 6: R=H, L=PPh 3 ). Despite 5 and 6 having a close similarity to 1, their dehydrodimerization proceeds according to a different scheme, as will be shown below. (7) was carried out using a procedure similar to that for 1, 9 i.e. 5 was oxidized by AgBF 4 in dichloromethane at À40°C, the solution was kept at this temperature for 2 h and finally reduced by (Z-C 6 H 6 ) 2 Cr. The target complex 7 was obtained in 40% yield and characterized by 1 H and 13 C NMR spectroscopy as well as by mass spectrometry. We found that the yield of 7 can be increased to 85±90% if either potassium t-butylate or triethylamine is used in the final reaction step. In order to determine the mechanism of the dehydrodimerization process, we studied the electrochemical behavior of complexes 5 and 7 by cyclic voltammetry in CH 2 Cl 2 solution (see Table 1).Complex 7 displays two one-electron reversible oxidation waves at 0.17 V (peak A) and 0.58 V (peak B) (see Fig. 1). Complex 5 oxidizes irreversibly at 0.77 V (see Fig. 2, peak C). The reverse scanning of potentials revealed new cathodic peaks at 0.67 V and 0.27 V (peaks D and E respectively). These peaks do not coincide with the reduction peaks A', B' of 7 .Thus, 7 is not an initial product of transformation of 5 Á ,i.e. dehydrodimerization of 5 proceeds by a different mechanism than that for complex 1 (Scheme 1). We believe Scheme 1.Scheme 2. Figure 1. CV of bis-vinylidene complex 7 at 20°C. ). In order to confirm the validity of the mechanism shown in Scheme 3, we studied the oxidative dehydrodimerization of the triphenylphosphine-substituted phenylvinylidene complex (Z 5 -C 5 H 5 )(CO)(PPh 3 )Mn=C=CHPh (6), since we expected the product of direct C (b) ÐC (b) that the isomers differ in the orientation of the phenyl group relative to the cyclopentadienyl ring. Oxidative dehydrodimerization of 6 was carried out under the same conditions as the analogous processes for 1 and 5. The bis-vinylidene complex 8 proved to be rather unstable, and was obtained in 20% yield. Its structure was confirmed by IR-, NMR 1 H, and 31 P spectroscopy and mass spectroscopy. According to the NMR spectra, complex 8 exists as a mixture of two diastereomers in 3:1 ratio.Electrochemical oxidation of 6 and 8 was studied by cyclic voltammetry (CV) in dichloromethane solution. The cyclic voltammogram of the bis-vinylidene complex 8 showed two reversible one-electron oxidation peaks at 0.19 V and 0.61 V (Fig. 3, peaks F and G respectively). The cyclic voltam...

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“…For example, Arbuzov reaction of P(OMe) 3 occurs during the reaction of the 19-e~ species (rç 5 -C 5 H 5 )(rç 6 -C 6 H 6 )Fe with P(OMe) 3 (17). As a 17-e" example, the intermediate alkynyl complex (?y 5 -C 5 H 5 )(dppe)Fe-C=CMe e+ formed upon oxidation and deprotonation of (*r-C 5 H 5 )(dppe)Fe=C=CHMe + undergoes carbon-carbon coupling at Cp of the alkynyl ligand to yield a vinylidene dimer (18). (dppe is l,2-bis(diphenylphosphino)ethane.)…”

Section: Reactions Within the Ligands Of Metal Radicalsmentioning

confidence: 99%

Photooxidation of Metal Carbynes

McElwee‐White

Kingsbury

Carter

1993

Photosensitive Metal—Organic Systems

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Radical cations formed upon photooxidation of the metal carbyne complexes (n 5 -C 5 H 5 )L 1 L 2 M≡CR (M is Mo or W; L 1 and L 2 are CO or P(OMe) 3 ; and R is alkyl or aryl) were found to be extremely reactive. Depending on the reaction conditions, either the radical cations exhibited the ligand-exchange and atom--abstraction processes that are typical of metal radicals, or the carbyne ligands underwent a series of highly unusual rearrangements to yield organic products. When organic products were generated, they were formed with good stereochemical and regiochemical control.REACTIVE ORGANIC FRAGMENTS CAN BE STABILIZED with transi tion metals so that they can be used for synthesis under ordinary reaction conditions. One example is the extensive utilization of metal carbenes in organic synthesis (2). It is thus somewhat surprising that there are so few reported cases of generation of organic products from the closely related metal carbynes. Although the chemistry of metal carbynes has been explored (2), most of the reported reactions involve conversion into other carbyne complexes by exchange of ancillary ligands; interconversion of car byne, carbene, and vinylidene complexes; or [2 + 2] cycloaddition with alkenes and alkynes followed by metathesis or polymerization. With the exception of polymers and metathesis products, organic species derived from the carbyne ligand are almost never generated.One method for inducing new modes of reactivity in metal complexes is one-electron (l-e~) oxidation. The differences in reaction rates between 18-e~ complexes and their 17-e~ counterparts can be quite dramatic (3-5). Reaction manifolds that are not available to an 18-e~ complex can thus become accessible to its corresponding 17-e~ radical cation. This chapter

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Synthesis and structure of a diiron divinylidene complex formed by oxidative carbon-carbon coupling

Cited by 98 publications

References 2 publications

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Oxidative dehydrodimerization of manganese vinylidene complexes (η⁵‐C₅R₅)(CO)(L)MnCCHPh (R = Me, L = CO; R = H, L = PPh₃)

Photooxidation of Metal Carbynes

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Synthesis and structure of a diiron divinylidene complex formed by oxidative carbon-carbon coupling

Cited by 98 publications

References 2 publications

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

Oxidative dehydrodimerization of manganese vinylidene complexes (η5‐C5R5)(CO)(L)MnCCHPh (R = Me, L = CO; R = H, L = PPh3)

Photooxidation of Metal Carbynes

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Oxidative dehydrodimerization of manganese vinylidene complexes (η⁵‐C₅R₅)(CO)(L)MnCCHPh (R = Me, L = CO; R = H, L = PPh₃)