Coordinated Olefins as Incipient Carbocations:  Catalytic Codimerization of Ethylene and Internal Olefins by a Dicationic Pt(II)−Ethylene Complex

Hahn, Christoph; Cucciolito, Maria Elena; Vitagliano, Aldo

doi:10.1021/ja0263386

Cited by 85 publications

(43 citation statements)

References 25 publications

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“…As either initial 5-exo or 6-endo cyclization in principle can lead to the [3.1.0] products, the precise mechanism of product formation is as yet unclear. As was pointed out by Vitagliano and co-workers, [116] the use of pincer ligands inhibits the bhydride elimination from Pt-alkyl intermediates that could potentially lead to side products.…”

Section: Homogeneous Platinum Catalysismentioning

confidence: 95%

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Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

2007

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The electrophilic activation of alkenes by transition-metal catalysts is a fundamental step in a rapidly growing number of catalytic processes. Although palladium is the best known metal for this purpose, the special properties of its third-row cousin platinum (strong metal-ligand bonds and slow substitution kinetics) have enabled the development of transformations that are initiated by addition to the C=C bonds by protic carbon, nitrogen, oxygen, and phosphorus nucleophiles, as well as alkene or arene nucleophiles. Additionally, reactivity profiles, which are often unique to platinum, provide wholly new reaction products. This Review concerns platinum-catalyzed electrophilic alkene activation reactions, with a special emphasis on the mechanistic properties of known systems, on the differences between platinum and palladium catalysts, and on the prospects for the development of new systems.

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Section: Homogeneous Platinum Catalysismentioning

confidence: 95%

“…(31)]. [116] By a simple change in ligand, cyclopropanes alternatively may be formed by a platinum-catalyzed intermolecular olefin dimerization [Eq. (32)].…”

Section: Carbon Nucleophiles: Platinum-catalyzed Hydrovinylation and mentioning

confidence: 99%

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

2007

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“…[86,87] In a related study (Scheme 29), they demonstrated that the same complexes can act as catalysts for the codimerization of ethene and internal alkenes (also known as the hydrovinylation reaction). [88] The Pd analogue was subsequently shown to catalyze the same co-dimerization activity, but cyclopropanation was observed as a significant side reaction. In some cases, the cyclopropanation turned out to be even the dominating product pathway.…”

Section: Palladium and Platinummentioning

confidence: 99%

Neutral Tridentate PNP Ligands and Their Hybrid Analogues: Versatile Non‐Innocent Scaffolds for Homogeneous Catalysis

Vlugt¹,

Reek²

2009

Angew Chem Int Ed

412

143

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Ligands in coordination chemistry and homogeneous catalysis are traditionally "static" spectators that do not actively participate in the catalytic cycle. However, such classic systems do not provide additional "handles" that could facilitate or trigger alternative productive reaction pathways. Recent advances in the use of novel nitrogen-centered pincer systems have unveiled interesting opportunities for cooperative catalysis. The chemistry of pyridine-derived, neutral ligands is discussed, with a specific focus on their non-innocent behavior and potential as facilitators for metal-mediated organic transformations. This overview should provide inspiration and an incentive to incorporate non-innocent ligands and their metal complexes within old and new homogeneously catalyzed reactions.

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“…The key to our pursuit was a recent report by Vitagliano et al of a dicationic Pt complex of a pyridyl bisphosphane pincer ligand [Pt(PNP)](BF 4 ) 2 (PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine) that catalyzes the dimerization of ethylene and 2-methyl-2-butene. [13,14] Intermolecular nucleophilic addition of 2-methyl-2-butene to coordinated ethylene was proposed, with turnover by a sequence of 1,2-hydride shifts. Most importantly, b-hydride elimination did not occur, since no open cis coordination sites were available, and this suggests that this complex might be capable of initiating cation formation while preserving the stereochemistry of the MÀC bond.…”

mentioning

confidence: 99%

Pd^II‐ and Pt^II‐Mediated Polycyclization Reactions of 1,5‐ and 1,6‐Dienes: Evidence in Support of Carbocation Intermediates

Koh¹,

Gagné²

2004

Angew Chem Int Ed

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Biomimetic polyolefin cascade reactions [1,2] represent some of the most challenging problems in reaction design, and their products are ubiquitous in the natural world.[3] Since the Brønsted-Lewis acids (BLAs) of Yamamoto et al. are the only known synthetic catalysts for asymmetric catalytic initiation of cation-olefin cyclizations, [4,5] [7] and Toyota, Ihara et al. [8] demonstrated that nucleophilic enols lead to carbocyclic products by b-hydride elimination [9] or protonation. [10] Although substituent effects [11] and stereochemical studies [6c] support a cationic and cyclic intermediate, respectively, the exact nature of this intermediate is unclear, and direct evidence for this cation is lacking.[12] We therefore initiated a plan that first gathered evidence supporting the intermediacy of the carbocyclic cation, while also determining whether it could function as a point for initiating new metal-mediated reactivity. The key to our pursuit was a recent report by Vitagliano et al. of a dicationic Pt complex of a pyridyl bisphosphane pincer ligand [Pt(PNP)](BF 4 ) 2 (PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine) that catalyzes the dimerization of ethylene and 2-methyl-2-butene. [13,14] Intermolecular nucleophilic addition of 2-methyl-2-butene to coordinated ethylene was proposed, with turnover by a sequence of 1,2-hydride shifts. Most importantly, b-hydride elimination did not occur, since no open cis coordination sites were available, and this suggests that this complex might be capable of initiating cation formation while preserving the stereochemistry of the MÀC bond.Our first approach to trapping the putative cation utilized the Pd analogue of the Vitagliano complex 1 and dienylphenol 3. Unlike direct Brønsted acid [4] and Hg II [15] activation/ polycyclization, Pd II prefers to coordinate and activate the least substituted alkene, [16] ensuring activation at the terminus. As shown in Scheme 1, the isolable C 6 F 5 CN adduct [17] efficiently (1 h, RT, CH 2 Cl 2 ) converted 3 to a new metalcontaining product devoid of alkene resonances ( 1 H NMR spectroscopy) as a 93:7 mixture of isomers according to 31 P NMR spectroscopy. This compound is stable up to 100 8C, though demetalation with NaBH 4 at room temperature rapidly [14b] yielded tricycle 4 in 90 % yield (two steps) and d.r. > 99:1. [18] Since a single diastereomer was observable in the crude demetalation product, we surmised that the isomer mixture for the Pd alkyl complex must result from epimers at the metal-containing stereocenter, a situation suggestive of competing chair-chair and boat-chair transition states, [19] each with a degree of concertedness in the CÀC/CÀO bondforming event, that is, a free carbocation is not likely formed [cf. Eq. (1)]. [1,20] Pincer complex [Pt(PPP)](BF 4 ) 2 (2, PPP = bis(2-diphenylphosphanylethyl)phenylphosphane), [21] derived from commercially available triphos, provided the intermediate alkyl complex with a slightly higher diastereoselectivity (96:4), and 4 in similarly high yield (87 %) and selectivity (> 99:1...

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Coordinated Olefins as Incipient Carbocations: Catalytic Codimerization of Ethylene and Internal Olefins by a Dicationic Pt(II)−Ethylene Complex

Cited by 85 publications

References 25 publications

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

Neutral Tridentate PNP Ligands and Their Hybrid Analogues: Versatile Non‐Innocent Scaffolds for Homogeneous Catalysis

Pd^II‐ and Pt^II‐Mediated Polycyclization Reactions of 1,5‐ and 1,6‐Dienes: Evidence in Support of Carbocation Intermediates

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Coordinated Olefins as Incipient Carbocations: Catalytic Codimerization of Ethylene and Internal Olefins by a Dicationic Pt(II)−Ethylene Complex

Cited by 85 publications

References 25 publications

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

Neutral Tridentate PNP Ligands and Their Hybrid Analogues: Versatile Non‐Innocent Scaffolds for Homogeneous Catalysis

PdII‐ and PtII‐Mediated Polycyclization Reactions of 1,5‐ and 1,6‐Dienes: Evidence in Support of Carbocation Intermediates

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Pd^II‐ and Pt^II‐Mediated Polycyclization Reactions of 1,5‐ and 1,6‐Dienes: Evidence in Support of Carbocation Intermediates