Activation of η5-Cyclopentadienyl Ligands toward Nucleophilic Attack through η5 → η3 Ring Slippage. Kinetics, Thermodynamics, and NMR Spectroscopy

Simanko, Walter; Сапунов, В. Н.; Schmid, Roland; Kirchner, Karl; Wherland, Scot

doi:10.1021/om9801195

Cited by 30 publications

(12 citation statements)

References 43 publications

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“…The same conclusion is drawn from 13 C{ 1 H} NMR spectroscopy. This has been demonstrated previously for 8a . The dynamic behavior of complexes 6 − 8 has been rationalized by an intramolecular enantiomeric equilibrium leading to an inversion of ruthenium as shown in Scheme .…”

Section: Resultssupporting

confidence: 68%

“…For the ligands, nonconjugated and conjugated olefins are among the most reactive substrates, while aromatic ligands, in particular the cyclopentadienyl anion, are among the least reactive . It was thus a surprise to find that tertiary phosphines react with the cationic 18-electron complexes [Ru(η 5 -C 5 H 5 )(η 4 -C 5 H 4 O)] 2 2+ ( 1 ) and [Ru(η 5 -C 5 H 5 )(η 4 -C 5 H 4 O)(L)] + (L = CH 3 CN ( 2 ), pyridine ( 3 ), thiourea ( 4 )) to give 1,1‘-disubstituted ruthenocenes [Ru(η 5 -C 5 H 4 PR 3 )(η 5 -C 5 H 4 OH)] + ( 12 ) (paths i and ii, Scheme ) as well as the anticipated 1,2-disubstituted ruthenocenes ( 13 ), formed via η 3 -cyclopentenoyl complexes [Ru(η 5 -C 5 H 5 )(η 3 -C 5 H 4 O−PR 3 )(L)] + (path iii, Scheme ). , Scheme gives an overview of the reactions hitherto analyzed on a synthetic level. Thus, 1 yields only 12 irrespective of the nature of the phosphine, whereas complexes 2 − 4 give 13 as well.…”

Section: Introductionmentioning

confidence: 99%

“…Preliminary kinetic studies with PMe 3 as the nucleophile have shown 1 that the formation of 12 is far more complex than that of 13 . In the initial step, PMe 3 attacks the metal center to give the η 3 -C 5 H 5 intermediate [ Ru(η 3 -C 5 H 5 )(η 4 -C 5 H 4 O)(PMe 3 )(L)] + which then undergoes an endo migration of PMe 3 to give [Ru(η 5 -C 5 H 4 PMe 3 )(η 5 -C 5 H 4 OH)] + ( 12a ) and/or free C 5 H 4 PMe 3 together with the half-sandwich complex [Ru(η 5 -C 5 H 4 OH)(PMe 3 ) 2 L] + ( 14a , 15 ), depending on L (Schemes and ). ,

2 …”

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of Nucleophilic Substitutions on Coordinated Polyenes and Polyenyls. 3.¹ Activation of η⁵-Cyclopentadienyl Ligands toward Nucleophilic Attack through η⁵ → η³ Ring Slippage and a Comparison with Reaction at C₅H₄O in [Ru(η⁵-C₅H₅)(η⁴-C₅H₄O)(L)]⁺ (L = CH₃CN, Pyridine, Thiourea)

Simanko¹,

Tesch²,

Сапунов³

et al. 1998

Organometallics

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Complexes of the types [Ru(η 5 -C 5 H 5 )(η 4 -C 5 H 4 O)] 2 (CF 3 SO 3 ) 2 (1) and [Ru(η 5 -C 5 H 5 )(η 4 -C 5 H 4 O)(L)]CF 3 SO 3 (L ) CH 3 CN (2), pyridine (3), thiourea (4)) react with tertiary phosphines to give (i) 1,1′-( 12) or (ii) 1,2-disubstituted ruthenocenes (13) depending primarily on the basicity of the entering phosphine and the nature of L. Path i proceeds via the intermediacy of, the hapticity of the C 5 H 5 ligand is changed from η 5 to η 3 while forming an additional Ru-P bond. The η 3 bonding mode was established by 1 H and 13 C{ 1 H} NMR spectroscopies. The kinetics of these reactions were studied in detail, providing enthalpies and entropies of both activation and reaction. The conversions to 6-8 are exothermic (∆H°) -5.5 to -16.9 kcal mol -1 ) but entropically unfavorable (∆S°) -44.8 to -19.0 cal K -1 mol -1 ). The activation parameters and rate constants vary little with the phosphine, suggesting a preequilibrium between η 5 and η 3 species of the starting complexes where the latter reacts with the entering phosphine in the rate-determining step. The new η 3 -C 5 H 5 complexes are, with the exception of 5, fluxional in solution due to an intramolecular enantiomeric equilibrium likely proceeding through a five-coordinate η 1 -C 5 H 5 intermediate. Path ii proceeds via η 3 -cyclopentenoyl complexes of the type [Ru(η 5 -C 5 H 5 )(η 3 -C 5 H 4 O-2-PR 3 )(L)] + (9-11). Furthermore, 3 and 4 react with small and basic phosphines PR 3 ) PMe 3 and Me 2 PCH 2 PMe 2 to give the half-sandwich complexes [Ru(η 5 -C 5 H 4 OH)(PR 3 ) 2 L] + (14, 15) together with free C 5 H 4 PR 3 (16).

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Section: Resultssupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

2 …”

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of Nucleophilic Substitutions on Coordinated Polyenes and Polyenyls. 3.¹ Activation of η⁵-Cyclopentadienyl Ligands toward Nucleophilic Attack through η⁵ → η³ Ring Slippage and a Comparison with Reaction at C₅H₄O in [Ru(η⁵-C₅H₅)(η⁴-C₅H₄O)(L)]⁺ (L = CH₃CN, Pyridine, Thiourea)

Simanko¹,

Tesch²,

Сапунов³

et al. 1998

Organometallics

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“…[17] Phenyl groups on the cyclopentadienyl are known to favor h 5 to h 3 ring slip since they stabilize the h 3 intermediate by conjugation with the aromatic rings. [18] Furthermore, Kirchner et al have characterized h 3 -cyclopentadienylruthenium complexes by NMR spectroscopy, [19] which were formed by reaction of h…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

Racemization of Secondary Alcohols Catalyzed by Cyclopentadienylruthenium Complexes: Evidence for an Alkoxide Pathway by Fast β‐Hydride Elimination–Readdition

Martín‐Matute

Åberg

Edin

et al. 2007

Chemistry A European J

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The racemization of sec-alcohols catalyzed by pentaphenylcyclopentadienyl-ruthenium complex 3a has been investigated. The mechanism involves ruthenium-alkoxide intermediates: reaction of tert-butoxide ruthenium complex 4 with a series of sec-alcohols with different electronic properties gave ruthenium complexes bearing a secondary alkoxide as a ligand. The characterization of these alkoxide complexes by NMR spectroscopy together with a study of the reaction using in situ IR spectroscopy is consistent with a mechanism in which the alkoxide substitution step and the beta-hydride elimination step occur without CO dissociation. The alkoxide substitution reaction is proposed to begin with hydrogen bonding of the incoming alcohol to the active ruthenium-alkoxide intermediate. Subsequent alkoxide exchange can occur via two pathways: i) an associative pathway involving a eta3-CpRu intermediate; or ii) a dissociative pathway within the solvent cage. Racemization at room temperature of a 1:1 mixture of (S)-1-phenylethanol and (S)-1-phenyl-[D4]-ethanol gave only rac-1-phenylethanol, and rac-1-phenyl-[D4]-ethanol, providing strong support for a mechanism in which the substrate stays coordinated to the metal center throughout the racemization, and does not leave the coordination sphere. Furthermore, racemization of a sec-alcohol bearing a ketone moiety within the same molecule does not result in any reduction of the original ketone, which rules out a mechanism where the intermediate ketone is trapped within the solvent cage. These results are consistent with a mechanism where eta3-Ph(5)C(5)-ruthenium intermediates are involved. Competitive racemization on nondeuterated and alpha-deuterated alpha-phenylethanols was used to determine the kinetic isotope effect kH/kD for the ruthenium-catalyzed racemization. The kinetic isotope effect kH/kD for p- X-C(6)H(4)CH(OH)CH(3) was 1.08, 1.27 and 1.45 for X=OMe, H, and CF3, respectively.

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“…A large number of ligands has been tested, as a survey of the Cambridge Structural Database (CSD) [17] shows. There are structurally characterized complexes with h 3 -coordinated Cp, in solution [18] and in the solid state, [19,20] as well as ligands with larger p systems, such as fluorenyl (C 13 H 9 À ), cyclopentha[def]phenantrenyl (C 15 H 9 À ), [21±28] and 1-hydronaphthalene (C 10 H 9 À ); [29,30] however, the most studied ligand is certainly indenyl. [21, 31±56] Since the early papers by the Hoffmann group [2,57,58] a large amount of work has been devoted to the theoretical understanding of haptotropic shifts.…”

Section: Introductionmentioning

confidence: 99%