The Isomerization of 1,3-Cyclooctadiene to 1,5-Cyclooctadiene <i>via</i> the Rhodium(I) π-Complex

Rinehart, Robert E.; Lasky, J. S.

doi:10.1021/ja01066a043

Cited by 59 publications

(9 citation statements)

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“…The resulting olefin hydride intermediate can proceed through a chain-walking mechanism to generate a 1,3-COD adduct, which can then insert to generate 1 . These products of chain walking are likely thermodynamically favorable, as 1,3-COD is a more stable isomer than 1,5-COD, and the terminal allylic cyclooctenyl fragment is a strongly coordinating ligand for the Ni center. , Regardless, reductive elimination from the putative 1,3-COD adduct explains the formation of free 1,3-COD in the reaction mixtures.…”

Section: Resultssupporting

confidence: 80%

Nickel-Mediated Dehydrogenative Aryl–Aryl Homocoupling of a Bulky Phosphino-Pyridine

2019

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Aryl−aryl bond formation through dehydrogenative coupling is an attractive transformation due to the atom and step economy of working with unfunctionalized C−H bonds. Pd catalysts are most common for this process, but Ni complexes have also been targeted as less expensive and more abundant alternatives. Here we report the ability of Ni 0 to activate a sterically encumbered phosphino-pyridine ligand with resulting dehydrogenative aryl−aryl homocoupling. The net H 2 equivalent is transferred to the coligand, resulting in hydrogenation of an olefin unit. We have investigated the mechanism of this process by stirring Ni(1,5-COD) 2 (COD = cyclooctadiene) and the PNPh ligand (PNPh = 2-((di-tert-butylphosphino)methyl)-6phenylpyridine) at mild temperatures to afford a Ni II complex. Isolation and characterization shows a PNPh ligand coordinated to Ni II through an activated pyridine carbon and the directing phosphine. The coligand is an activated allylic cyclooctenyl fragment resulting from partial hydrogenation of 1,5-COD. We propose that this intermediate reacts intermolecularly with 1 equiv of itself, enabling the isolation of a bi-PNPh compound (bi-PNPh = 2,2′-bis((di-tert-butylphosphino)methyl)-6,6′diphenyl-3,3′-bipyridine), coupled through the activated pyridyl position. This dehydrogenative coupling, although stoichiometric, demonstrates the potential of Ni 0 -mediated C(sp 2 )−H activation and homocoupling for synthetic applications.

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Section: Resultssupporting

confidence: 80%

Nickel-Mediated Dehydrogenative Aryl–Aryl Homocoupling of a Bulky Phosphino-Pyridine

2019

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“…This lack of deuteriation at H3 is a significant measure of no olefin isomerization to the corresponding (Z)-citraconic or (E)-mesaconic acid isomers (8), although rhodium(I) and -(III) species are well-known as olefin isomerization catalysts. [29][30][31][32][33][34] From examination of the C2 methine carbon resonance (Figure 2), isotopomers 6, 9, and possibly 10 can also be distinguished. The unlabeled (perprotio) methylsuccinic acid methine resonates at δ 37.73 ppm [identified as (a) in Figure 2] (from a sample spiked with authentic methylsuccinic acid), and the three signals immediately upfield from this signal arise from successive β-isotope shifts (0.06-0.08 ppm) concomitant with compounds 7, 6, and 9 (37.66 (b), 37.58 (c), and 37.52 ppm (d), respectively).…”

Section: Resultsmentioning

confidence: 99%

Isotopic Enrichment by Asymmetric Deuteriation. An Investigation of the Synthesis of Deuteriated (S)-(−)-Methylsuccinic Acids from Itaconic Acid

1996

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Two different asymmetric hydrogenation methodologies based on gaseous hydrogen at 1 atm pressure and transfer hydrogenation from the decomposition of formic acid, in the presence of a rhodium catalyst, have been used to prepare (S)-(-)-methylsuccinic acid enriched with the deuterium isotope. NMR and mass spectroscopic evidence indicates that complex labeling occurs. We interpret this labeling pattern as the result of an equilibrium which exists between the olefin and a catalyst-alkyl intermediate in a Wilkinson-type mechanism. This phenomenon has not been reported in similar experiments with (E)-phenylitaconic acid where the expected cis-addition of deuterium from either deuterium gas at 1 atm, or deuteriated formic acid under transfer hydrogenation conditions, was observed. In our studies reducing itaconic acid (methylenebutanedioic acid), there was no loss of asymmetric induction (above 90% ee), approximately 2.4 deuterons were incorporated into (S)-(-)-methylsuccinic acid, a ratio of 1.8:1 methyl: methine deuteriation was observed, and there was no evidence for olefin isomerization into conjugation with both carboxylic acid groups. Following these isotopic enrichment studies, we present the first evidence for reversible transfer addition of deuterium to methylsuccinic acid, either by gaseous or transfer hydrogenation at atmospheric pressure. Such a mechanism has recently been eliminated for reduction at elevated pressures. These results have general applicability to the synthesis of isotopically labeled homochiral substituted carboxylic acids and also in interpreting the 13 C NMR data which are generated by the simultaneous presence of several deuterium containing isotopomers.

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“…If Hmv+2(CH2=CDC2H5) undergoes readdition of hydride to Ci (eq 12) rather than displacement of CH2=CDC2H5 by CH2=CHC2H6, further reaction (eq 13, 14, and 15) will yield CH3CD= CHCH3. This occurs about one-quarter of the time in a rhodium(I)-HCl catalyst system.6 If deuterium in Dmv+2(CH2=CHC2H5) adds to Ci, the isomeric deuteriobutene, CH2DCH=CHCH3, results (eq 16- 19). This happens about one-fifteenth of the time with the rhodium catalyst.6 It is not proposed that reaction is limited to the steps in Scheme IV.…”

Section: Discussionmentioning

confidence: 99%

The Mechanism of Isomerization of Olefins with Transition Metal Catalysts

Cramer¹,

Lindsey²

1966

J. Am. Chem. Soc.

189

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The Isomerization of 1,3-Cyclooctadiene to 1,5-Cyclooctadiene via the Rhodium(I) π-Complex

Cited by 59 publications

References 1 publication

Nickel-Mediated Dehydrogenative Aryl–Aryl Homocoupling of a Bulky Phosphino-Pyridine

Nickel-Mediated Dehydrogenative Aryl–Aryl Homocoupling of a Bulky Phosphino-Pyridine

Isotopic Enrichment by Asymmetric Deuteriation. An Investigation of the Synthesis of Deuteriated (S)-(−)-Methylsuccinic Acids from Itaconic Acid

The Mechanism of Isomerization of Olefins with Transition Metal Catalysts

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