Stabilization of small-ring acetylenes by complex formation with platinum

Bennett, Martin A.; Robertson, G. B.; Whimp, P. O.; Yoshida, Tomohiro

doi:10.1021/ja00744a056

Cited by 56 publications

(22 citation statements)

References 4 publications

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“…[11,26] Wegen des dem Alkin durch die starke Rückbindung von Elektronendichte in das antibindende p*-Orbital aufgezwungenen "Olefincharakters" lassen sich selbst so gespannte und reaktive Fragmente wie Cycloheptin oder Arine stabilisieren (Abbildung 5). [27,28] Generell können Komplexe vom "Metallacyclopropen-" oder "Metallacyclopropan-Typ" als C-Nukleophile gelten.…”

Section: Grundlagen Der Carbophilen Aktivierungunclassified

Katalytische carbophile Aktivierung: Platin‐ und Gold‐π‐Säuren als Katalysatoren

2007

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Platin‐ und Goldkatalysatoren gewinnen aufgrund ihrer hohen Effizienz und erstaunlichen Vielfalt für atomökonomische Umsetzungen rasch an Bedeutung. Dabei erlaubt es die Korrelation zwischen ihrem chemischen Verhalten und den vorhandenen Strukturdaten, der bekannten Koordinationschemie und den auf relativistischen Effekten beruhenden Besonderheiten ihrer metallorganischen Derivate, grundlegende Prinzipien der katalytischen carbophilen Aktivierung durch π‐Säuren zu formulieren. Platin‐ und Goldkomplexe sind keinesfalls nur ein umweltfreundlicher Ersatz für stöchiometrische π‐Säuren, sondern sie erweitern das klassische Reaktivitätsspektrum signifikant. Die in der Literatur geläufigen, aber scheinbar widersprüchlichen Erklärungen ihres Verhaltens auf Basis von Metallcarbenen oder metallstabilisierten, “nichtklassischen” Carbokationen als reaktiven Zwischenstufen liefern bei genauer Betrachtung eine vereinheitlichte Grundlage für das Verständnis dieses faszinierenden Gebiets. Hier gilt das Hauptaugenmerk der Verbesserung bekannter sowie der Entwicklung neuer Kupplungs‐, Cycloisomerisierungs‐ und Gerüstumlagerungsreaktionen. Auch der Einsatz Platin‐ und goldkatalysierter Transformationen in Naturstoffsynthesen wird diskutiert.

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Section: Grundlagen Der Carbophilen Aktivierungunclassified

Katalytische carbophile Aktivierung: Platin‐ und Gold‐π‐Säuren als Katalysatoren

2007

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“…Since cyclohexyne 56 is still too reactive to be isolated as such, the chemical proofs of its intermediate existence again rest on trapping and matrix isolation experiments. For example, it has been reacted with tris(triphenylphosphine)platinum(0) to provide a stable platinum complex [52], and trimerization leads to dodeca hydrotriphenylene (see below) [40,48].…”

Section: Cyclohexyne and Its Derivativesmentioning

confidence: 99%

“…As described for cyclohexyne (see above), the platinum complex 75 was obtained from intermediately generated 72 [52]. Its X-ray structural analysis shows that the triple bond deviates from linearity by ca.…”

Section: Cycloheptyne and Its Derivativesmentioning

confidence: 99%

Angle‐Strained Cycloalkynes

Hopf¹,

Grunenberg²

2009

Strained Hydrocarbons

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IntroductionAccording to the sp-hybridization model, the carbon-carbon triple bond possesses a linear structure, and indeed, many alkynes fulfill this prediction. High level ab initio calculations [1] of isolated alkyne molecules, as well as gas phase electron diffraction experiments [2] reveal their linear minimum structure. On the other hand, given that the C C-R bending force constant becomes intrinsically smaller for substituted alkynes and polyynes, crystal packing effects may lead to deviations from strictly linear geometries [3]. From a dynamic point of view even in the case of acetylene one has to include the -albeit reduced -flexibility of the carboncarbon triple bond in order to describe, for example, the vinylidene acetylene rearrangement (see below) [4]. Further, the linear sp-hybrid picture only holds true for the electronic ground state. Cis-and trans-bent configurations are known in the case of low-lying electronic states [5]. Nevertheless, many alkynes correspond to the prediction of linearity due to the sp-hybrid model, and we have collected a selection of typical examples, reaching from the parent compound acetylene 1 via a few alkyl 2-4 and aryl acetylenes 5-7 to a functionalized acetylene, dimethyl acetylenedicarboxylate 8, in Scheme 7.1, together with the appropriate references [1, 2, 6-11], all dating from the recent literature.The easiest way to distort a triple bond is to incorporate it into a sufficiently small ring structure. The question, of course, is what this ring size is, and from what ring size on the respective cycloalkynes can we isolate compounds, that can be worked with under normal laboratory conditions [12]. Rather than using the nonspecific term 'distorted cycloalkyne' Krebs [12] prefers to speak of 'angle-strained cycloalkynes'. Since it is easier to deform a C C-C arrangement than its more hydrogenated olefinic and saturated analogs, relatively large angle deformations are possible in cycloalkynes without significant changes in energy. Krebs arbitrarily considers all cycloalkynes in which the C C-C angle is deformed by more than 10° as angle-strained [12]. Accepting this definition, the stable cyclononyne (see below) is an angle-strained cycloalkyne, whereas cyclodecyne is not.

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“…Where observable, this results in a splitting of the vinylic proton resonance into a triplet from virtual coupling to two equivalent phosphorus nuclei. For the cis isomer, coupling from the cis phosphorus atom is too small to be resolvable, so that the vinylic proton resonance is split into a doublet from coupling to only the trans phosphorus nucleus (4J(P-H,) -10 Hz) (7,17).…”

Section: Stereochemistry Of Reaction Productsmentioning

confidence: 99%

“…The disposition of platinum arid hydrogen in the alkenyl function may be determined from the magnitude of 3J(Pr-H,,), for \vliich it has been shown (7,(17)(18)(19) that the order observed is trans > cis >> geinina!. However, it has zlso been found (16) that the value of 3J(Pt-H,.)…”

Section: Stereochemistry Of Reaction Productsmentioning

confidence: 99%

Chemistry of metal hydrides. Part XIX. Stereochemical changes at platinum during the insertion of acetylenes with platinum(II) hydrides

Clark¹,

Fiess²,

Wong³

1977

Can. J. Chem.

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The reactions of trans-[PtH(PEt3)2(acetone)]+ and trans-[PtH(PEt3)2(CO)]+ with a variety of acetylenes are described. The geometries of the products with respect to the platinum centre and to the stereochemistry of the alkenyl group have been determined on the basis of their 1H nmr parameters. For reactions with the cation containing acetone, and particularly from a variable temperature 1H nmr study of its reaction with 2-butyne in the presence of water, the insertion pathway is shown to be entirely analogous to that for olefin insertion, involving an initial displacement of the trans ligand by acetylene, isomerization to a cis-like intermediate, migratory insertion rearrangement, and re-combination with an appropriate ligand to give either cis or trans platinum products. The insertion pathway with the carbonyl cation is dependent on the nature of the acetylene; for non-activated or weakly activated acetylenes insertion occurs via five-coordinate intermediates, but with strongly activated acetylenes, the same mechanism as with the acetone cation appears to occur, involving reversible loss of carbon monoxide.

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Stabilization of small-ring acetylenes by complex formation with platinum

Cited by 56 publications

References 4 publications

Katalytische carbophile Aktivierung: Platin‐ und Gold‐π‐Säuren als Katalysatoren

Katalytische carbophile Aktivierung: Platin‐ und Gold‐π‐Säuren als Katalysatoren

Angle‐Strained Cycloalkynes

Chemistry of metal hydrides. Part XIX. Stereochemical changes at platinum during the insertion of acetylenes with platinum(II) hydrides

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