Matrix photochemistry of (.eta.5-cyclopentadienyl)bis(ethene)rhodium and (.eta.5-cyclopentadienyl)(ethene)carbonylrhodium:  a test-bed for intermediates in C-H activation

Haddleton, David M.; McCamley, Andrew; Perutz, Robin N.

doi:10.1021/ja00214a025

Cited by 50 publications

(21 citation statements)

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“…Numerous ultrafast studies have now been performed for metal carbonyl complexes, and it is well established that CO dissociation reactions take place readily in this wavelength region − Moreover, the lack of an observable dependence of φ CH with added CO is completely consistent with extremely fast formation of a monocarbonyl photoproduced intermediate from a dissociative LF excited state. Subsequently, the intermediate will react rapidly with the hydrocarbon substrate (8.7 M n -pentane) before CO (ca.…”

Section: Discussionmentioning

confidence: 99%

“…Upon photochemical excitation of (η 5 -C 5 R 5 )ML 2 and (η 5 -C 5 R 5 )ML(H) 2 (R = H, Me; M = Rh, Ir; L = olefin, PR 3 , CO), it has been established that the intermolecular C−H activation stems from an unsaturated 16-electron (η 5 -C 5 R 5 )ML primary photoproduct that rapidly forms a solvent-adduct complex, (η 5 -C 5 R 5 )ML···S, in even normally inert solvents (S), before reacting with R−H bonds. Following initial synthetic and competitive rate investigations, − various experimental techniques have been employed to elucidate the mechanisms of these C−H activation reactions; these have involved matrix isolation, , solvation in liquefied rare gases, steady-state photolysis, and laser-flash photolysis . The rates of alkane C−H bond activation to (η 5 -C 5 H 5 )Rh(CO) 2 in the gas phase 10 and to (η 5 -C 5 Me 5 )Rh(CO)X (X = Kr, Xe) in liquefied noble gas solvents at low temperature have also been reported.…”

Section: Introductionmentioning

confidence: 99%

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Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Purwoko

Lees

1996

Inorg. Chem.

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The intermolecular C−H bond activation photochemistry of (HBPz‘3)Rh(CO)2 (Pz‘ = 3,5-dimethylpyrazolyl) has been investigated in various alkane solutions at 293 K. Excitations have been performed at 313−458 nm into the lowest energy absorption band of this complex, and the reactions have been monitored throughout photolysis by in situ UV−visible and FTIR spectroscopy. The spectral results reveal that the photochemistry is exceptionally clean and that the reagent complex can be completely converted to the corresponding (HBPz‘3)Rh(CO)(R)H photoproduct at each of the irradiation wavelengths. Absolute photochemical quantum efficiencies (φCH) for these reactions have been determined and illustrate that the intermolecular C−H bond activation process is strongly wavelength dependent. Very effective conversion (φCH = 0.31−0.34) is attained upon near-UV excitation at 313 or 366 nm. In contrast, inefficient conversion (φCH = 0.010−0.011) is observed on visible excitation at 458 nm. The differences in reactivities are interpreted on a photophysical scheme in which the irradiations produce two ligand field (LF) electronically excited states with different primary photoproducts. The thermal chemistry of (HBPz‘3)Rh(CO)2 in room-temperature solution is characterized as involving facile η3 ↔ η2 ligand interconversions. Accordingly, the complex is readily protonated to form [{η2-HBPz‘2(Pz‘H)}Rh(CO)2]BF4, and when PPh3 is added to a solution of (HBPz‘3)Rh(CO)2, the ligand substitution product, (HBPz‘3)Rh(CO)PPh3, is formed immediately. In contrast, there is no evidence of thermal ligand scavenging of (HBPz‘3)Rh(CO)2 by pyridine and upon irradiation in pyridine solutions the photochemistry is dominated by the C−H activation reaction of the hydrocarbon solvent. In triethylsilane solutions the observed spectral changes reveal that intermolecular Si−H bond activation takes place readily on excitation of (HBPz‘3)Rh(CO)2 at 366 nm. The thermal chemistry of the analogous square planar complex (H2BPz2)Rh(CO)2 has been investigated, and the complex has been found to be reactive toward PPh3 and not R−H in room-temperature solution under dark conditions. These experimental observations imply that the long-wavelength (458 nm) photochemistry and thermal chemistry of (HBPz‘3)Rh(CO)2 are associated with a (η2-HBPz‘3)Rh(CO)2 intermediate that is unable to facilitate hydrocarbon C−H bond activation. Importantly, the observed results also suggest that the short-wavelength (313, 366 nm) photochemistry proceeds via an extremely short-lived monocarbonyl (HBPz‘3)Rh(CO) complex that undergoes efficient C−H activation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Purwoko

Lees

1996

Inorg. Chem.

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“…The matrix isolation equipment has been described previously. 67 Samples were deposited onto a CsI window cooled by an Air Products CS202 closed-cycle Displex refrigerator to 20 K. The compound [Re(η 5 -C 5 H 5 )(CO) 2 (η 2 -C 6 F 6 )] was sublimed from a right-angled glass tube (at 323 K) at the same time as matrix gas (BOC Research Grade argon, 99.999%) was deposited through a separate inlet. Typical deposition rates were 2 mmol h Ϫ1 for Ar.…”

Section: Matrix Isolationmentioning

confidence: 99%

Structure and dynamics of the η2-hexafluorobenzene complexes [Re(η5-C5H4R)(CO) 2(η2-C6F6)] (R = H or Me) and [Rh(η5-C5Me5)(PMe3)( η2-C6F6)]

Higgitt¹,

Klahn²,

Moore³

et al. 1997

J. Chem. Soc., Dalton Trans.

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“…These reactions have been shown by time resolved laser spectroscopy to involve the 16 electron intermediate CpRh(C 2 H 4 ). 17 The Rh(silyl)-(hydride)(alkene) species were shown to be active hydrosilation catalysts, and in the case of HSiEt 3 , a J Si-H value of 12 Hz was reported. 18 Since the two isomers of CpRh(SiR 3 )(H)(C 2 H 4 ) are enantiomers, their interconversion cannot be followed using routine NMR methods.…”

Section: Introductionmentioning

confidence: 99%

Photochemical reactions of (η⁵-cyclopentadienyl)bis(t-butylacrylate) rhodium with silanes: Dynamics of isomer interconversion via Rh(η²-silane) species

2004

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The compound CpRh(C(2)H(3)CO(2)(t)Bu)(2) 1 has been synthesised as a mixture of two pairs of interconverting isomers which differ in the relative orientations of the alkene substituents. The four isomers have been fully characterised by NMR spectroscopy. When complex 1 is photolysed in the presence of a silane, HSiR(2)R'R(2)R'= Et(3), Me(3), HEt(2), (OMe)(3) and Me(2)Cl] the corresponding Si-H oxidative addition products CpRh(SiR(2)R')(H)(C(2)H(3)CO(2)(t)Bu) and CpRh(H)(2)(SiR(2)R')(2) are formed. The Rh(III) complexes CpRh(SiR(2)R')(H)(C(2)H(3)CO(2)(t)Bu) exist in two isomeric forms of comparable energy which interconvert in an intramolecular process that does not involve a reversible [1,3] hydride or [1,3] silyl migration. The hydride (1)H NMR resonances for these species consequently broaden before coalescing into a single peak. For R(2)R'= Et(3), the activation parameters for interchange from the major to minor isomer were Delta H++= 60.2 +/- 2 kJ mol(-1) and Delta S++= 8 +/- 9 J mol(-1) K(-1), while for R(2)R'= Me(3) and Et(2)H, Delta H++= 61.5 +/- 1 kJ mol(-1), Delta S++= 6 +/- 5 J mol(-1) K(-1), and Delta H++= 61.8 +/- 3 kJ mol(-1), Delta S++= 12 +/- 9 J mol(-1) K(-1) respectively for conversion from the major isomer to the minor. For these complexes an eta(2)-Rh-H-Si transition state or intermediate is consistent with the evidence. When R(2)R'=(OMe)(3) and Me(2)Cl the change in appearance of the hydride resonances is more complex, with the activation parameters for interchange from the major to minor isomer for the former species being Delta H++= 78.3 +/- 2 kJ mol(-1) and Delta S++= 30 +/- 7 J mol(-1) K(-1) while for Me(2)Cl the barrier proved too high to measure before decomposition occurred. The complex spectral changes could be simulated when a discrete eta(2)-Rh-H-Si intermediate was involved in the isomer interconversion process and hence silane rotation in all these systems is proposed to involve two isomers of CpRh(eta(2)-HSiR(2)R')(C(2)H(3)CO(2)(t)Bu).

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Matrix photochemistry of (.eta.5-cyclopentadienyl)bis(ethene)rhodium and (.eta.5-cyclopentadienyl)(ethene)carbonylrhodium: a test-bed for intermediates in C-H activation

Cited by 50 publications

References 1 publication

Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Structure and dynamics of the η2-hexafluorobenzene complexes [Re(η5-C5H4R)(CO) 2(η2-C6F6)] (R = H or Me) and [Rh(η5-C5Me5)(PMe3)( η2-C6F6)]

Photochemical reactions of (η⁵-cyclopentadienyl)bis(t-butylacrylate) rhodium with silanes: Dynamics of isomer interconversion via Rh(η²-silane) species

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Matrix photochemistry of (.eta.5-cyclopentadienyl)bis(ethene)rhodium and (.eta.5-cyclopentadienyl)(ethene)carbonylrhodium: a test-bed for intermediates in C-H activation

Cited by 50 publications

References 1 publication

Photochemical C−H Bond Activation Reactivity of (HBPz‘3)Rh(CO)2 (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Photochemical C−H Bond Activation Reactivity of (HBPz‘3)Rh(CO)2 (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Structure and dynamics of the η2-hexafluorobenzene complexes [Re(η5-C5H4R)(CO) 2(η2-C6F6)] (R = H or Me) and [Rh(η5-C5Me5)(PMe3)( η2-C6F6)]

Photochemical reactions of (η5-cyclopentadienyl)bis(t-butylacrylate) rhodium with silanes: Dynamics of isomer interconversion via Rh(η2-silane) species

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Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Photochemical C−H Bond Activation Reactivity of (HBPz‘₃)Rh(CO)₂ (Pz‘ = 3,5-Dimethylpyrazolyl) in Alkane Solutions

Photochemical reactions of (η⁵-cyclopentadienyl)bis(t-butylacrylate) rhodium with silanes: Dynamics of isomer interconversion via Rh(η²-silane) species