Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex

Hoyano, James K.; Graham, W. A. G.

doi:10.1021/ja00377a032

Cited by 417 publications

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“…Although the differences in the barriers are similar for the two functionals, the obvious absolute discrepancy between these two functionals prompted us to perform additional calculations at the coupled cluster single and double (CCSD) level on the geometries obtained at both B3LYP and PBE levels. The "CCSD/B3LYP barriers" for CpRh(CO) are 4.7, 5.2, and 4.7 kcal mol −1 for CH 4 , C 2 H 6 , and C 3 H 8 , respectively, whereas those for the bulky, but electron-rich, Cp*Rh(CO) complex are 4.5, 4.8, and 4.4 kcal mol −1 for CH 4 , C 2 H 6 , and C 3 H 8 . The relative barrier for activating different C─H bonds is also a crucial issue.…”

Section: Resultsmentioning

confidence: 99%

“…The facile activation of methane is considered a "holy grail" for chemists (2). The use of transition metals in order to provide a way to activate carbon─hydrogen (C─H) bonds in hydrocarbons offers the potential to address this problem, and useful processes have been developed including alkane dehydrogenation, arene borylation, and alkane metathesis.The early reports of alkane activation involved an initial photodissociation of a ligand, from a five-coordinate cyclopentadienyl rhodium(I) or iridium(I) complex to form a coordinatively unsaturated intermediate (3,4). This reactive species subsequently attacks and oxidatively adds a C─H bond to form the alkyl hydride product.…”

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confidence: 99%

“…The early reports of alkane activation involved an initial photodissociation of a ligand, from a five-coordinate cyclopentadienyl rhodium(I) or iridium(I) complex to form a coordinatively unsaturated intermediate (3,4). This reactive species subsequently attacks and oxidatively adds a C─H bond to form the alkyl hydride product.…”

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confidence: 99%

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Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)

George

Hall²,

Jina³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Fast time-resolved infrared spectroscopic measurements have allowed precise determination of the rates of activation of alkanes by Cp′Rh(CO) (Cp 0 ¼ η 5 -C 5 H 5 or η 5 -C 5 Me 5 ). We have monitored the kinetics of C─H activation in solution at room temperature and determined how the change in rate of oxidative cleavage varies from methane to decane. The lifetime of CpRh(CO)(alkane) shows a nearly linear behavior with respect to the length of the alkane chain, whereas the related Cp*Rh(CO)(alkane) has clear oscillatory behavior upon changing the alkane. Coupled cluster and density functional theory calculations on these complexes, transition states, and intermediates provide the insight into the mechanism and barriers in order to develop a kinetic simulation of the experimental results. The observed behavior is a subtle interplay between the rates of activation and migration. Unexpectedly, the calculations predict that the most rapid process in these Cp′Rh (CO)(alkane) systems is the 1,3-migration along the alkane chain. The linear behavior in the observed lifetime of CpRh(CO)(alkane) results from a mechanism in which the next most rapid process is the activation of primary C─H bonds (─CH 3 groups), while the third key step in this system is 1,2-migration with a slightly slower rate. The oscillatory behavior in the lifetime of Cp*Rh(CO)(alkane) with respect to the alkane's chain length follows from subtle interplay between more rapid migrations and less rapid primary C─H activation, with respect to CpRh(CO)(alkane), especially when the CH 3 group is near a gauche turn. This interplay results in the activation being controlled by the percentage of alkane conformers.A lkanes are generally unreactive molecules and the lack of ability to utilize such feedstock has thwarted the widespread use of methane, the main component of natural gas, as a feedstock to produce synthetically useful compounds even though this inexpensive source is widely available (1). The facile activation of methane is considered a "holy grail" for chemists (2). The use of transition metals in order to provide a way to activate carbon─hydrogen (C─H) bonds in hydrocarbons offers the potential to address this problem, and useful processes have been developed including alkane dehydrogenation, arene borylation, and alkane metathesis.The early reports of alkane activation involved an initial photodissociation of a ligand, from a five-coordinate cyclopentadienyl rhodium(I) or iridium(I) complex to form a coordinatively unsaturated intermediate (3,4). This reactive species subsequently attacks and oxidatively adds a C─H bond to form the alkyl hydride product. There has been considerable research effort directed toward understanding this key reaction in order to allow the full exploitation of the C─H activation process. The photochemistry of Cp 0 RhðCOÞ 2 [Cp 0 ¼ ðη 5 -C 5 R 5 Þ, R ¼ H (Cp) or CH 3 (Cp*)] has played an important role in developing our understanding particularly because the infrared νðC─OÞ bands are a useful spectroscopic tool for charac...

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)

George

Hall²,

Jina³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…O rganometallic complexes of the cyclopentadienyl (Cp) and trispyrazolylborate (Tp) type have been shown to activate a variety of COH bonds in alkanes and arenes (1)(2)(3)(4)(5)(6)(7)(8)(9). However, studies on the activation of alkanes and arenes containing reactive functional groups have received far less attention in the literature.…”

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confidence: 99%

The activation of alkyl cyanides using a rhodiumtrispyrazolylborate complex

Vetter

Rieth

Jones

2007

Proc. Natl. Acad. Sci. U.S.A.

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O rganometallic complexes of the cyclopentadienyl (Cp) and trispyrazolylborate (Tp) type have been shown to activate a variety of COH bonds in alkanes and arenes (1-9). However, studies on the activation of alkanes and arenes containing reactive functional groups have received far less attention in the literature. Hartwig and coworkers (10-12) have been successful in the hydroborylation of mono-and disubstituted arenes using transition metal catalysts. The borylation of the arene ring is believed to occur after oxidative addition of the ring COH bond without interference of reaction with the functional group. Smith (13,14) has even shown that haloarenes can be borylated and functionalized without affecting the carbon-halogen bond. Although numerous examples are presented for the functionalization of substituted arenes (15), the functionalization of alkanes containing reactive functional groups is somewhat restricted, perhaps because some of the functional groups on the alkanes are more reactive toward the catalysts and do not allow for COH activation. In addition, some functional groups (e.g., OH) are known to make the adjacent COH bonds more reactive in alkanes (16).We recently reported the activation of 1-, 2-, and 3-chloropentanes using a trispyrazolylborate rhodium complex (17). It was determined that the [TpЈRh(L)] fragment did not oxidatively cleave the COCl bond of the chloroalkane, as would have been expected given the relative bond strengths of COH (Ϸ100 kcal) vs. COCl (80 kcal) bonds (18) and the literature precedence that exists for the oxidative addition of COCl bonds to Rh(I) and Ir(I) metal systems (15,19). Surprisingly, the [TpЈRh(L)] fragment reacted exclusively with the terminal COH bonds of the alkane to give the substituted haloalkyl hydride complex. Here, we extend the investigation of the activation of hydrocarbon COH bonds to include substrates containing the nitrile functional group (OC'N).The COH bond activation of acetonitrile has been documented in the past. Teuben and coworkers (20) have reported the COH activation of acetonitrile via a -bond metathesis using Cp* 2 LnCH(SiMe 3 ) 2 . Jesson and coworkers (21) have also documented the formation of the cyanomethyl hydride as a result of activation of acetonitrile using (dmpe) 2 M(Np)H (M ϭ Fe, Ru; Np ϭ 2-naphthyl). The scission of the COCN bond of acetonitrile has also been reported by Parkin and coworkers (22), Brookhart and coworkers (23, 24), Nakazawa et al. (25), and Jones and coworkers (26). Of particular interest is the work by Brookhart using a similar Cp*Rh(PMe 3 ) system (23), which is known to undergo COH bond activation in the presence of alkanes and arenes (3,27). However, in the presence of nitriles and triphenylsilane, the complex promotes the cleavage of the COCN bond.To demonstrate the diversity of nitrile reactivity with low valent metals, our group has also investigated the reactions of aromatic, allylic, and alkyl nitriles using [(dippe)NiH] 2 (28-30). In these studies, 2 coordination of the CN bond to the Ni metal cent...

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“…In a sense, the culmination of these observations of intramolecular and intermolecular aryl C-H oxidative addition appeared in 1982 when Bergman and then Graham reported the first examples of intermolecular addition of alkane C-H bonds to give stable alkyl iridium hydrides (49,50). Clearly the first example of such reactivity must constitute a major milestone and this breakthrough has justly achieved celebrity.…”

Section: Oxidative Addition Of C-h Bonds: Early Examplesmentioning

confidence: 99%

Organometallic C—H Bond Activation: An Introduction

Goldman¹,

Goldberg²

2004

ACS Symposium Series

113

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An introduction to the field of activation and fimctionalization of C-H bonds by solution-phase transition -metal-based systems is presented, with an emphasis on the activation of aliphatic C-H bonds. The focus of this chapter is on stoichiometric and catalytic reactions that operate via organometallic mechanisms, i.e., those in which a bond is formed between the metal center and the carbon undergoing reactionThe carbon-hydrogen bond is the un-functional group. Its unique position in organic chemistry is well illustrated by the standard representation of organic molecules: the presence of C-H bonds is indicated simply by the absence of any other bond. This "invisibility" of C-H bonds reflects both their ubiquitous nature and their lack of reactivity. With these characteristics in mind it is clear that if the ability to selectively fiinctionalize C-H bonds were well developed, it could potentially constitute the most broadly applicable and powerful class of transformations in organic synthesis. Realization of such potential could revolutionize the synthesis of organic molecules ranging in complexity from methanol to the most elaborate natural or unnatural products.The following chapters in this volume offer a view of many of the current leading research efforts in this field, in particular those focused on the activation

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Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex

Cited by 417 publications

References 0 publications

Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)

Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)

The activation of alkyl cyanides using a rhodiumtrispyrazolylborate complex

Organometallic C—H Bond Activation: An Introduction

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Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex

Cited by 417 publications

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Understanding the factors affecting the activation of alkane by Cp ′ Rh(CO) 2 (Cp ′ = Cp or Cp*)

Understanding the factors affecting the activation of alkane by Cp ′ Rh(CO) 2 (Cp ′ = Cp or Cp*)

The activation of alkyl cyanides using a rhodiumtrispyrazolylborate complex

Organometallic C—H Bond Activation: An Introduction

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Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)

Understanding the factors affecting the activation of alkane by Cp ^′ Rh(CO) ₂ (Cp ^′ = Cp or Cp*)