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

Abstract

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.

Redox Activation of Alkene Ligands in Platinum Complexes with Non-innocent Ligands

“…26,28,29 The greater electrophilicity of cationic versus neutral platinum olefin complexes has been well-documented, especially by Natile and co-workers. [28][29][30] The redox-active character of the amidophenolate allowed us to "turn on" the electrophi- Redox ActiWation of Alkene Ligands licity of the coordinated alkene. Whereas 1 is unreactive toward nucleophiles, the oxidized derivatives rapidly and stereospecifically add alkoxides at carbon.…”

Gold‐Catalyzed Intramolecular [3+2] Cycloadditions of 1‐Aryl‐1‐allene‐6‐enes

“…Use of AgSbF 6 improved the cyclization efficiency, giving the trans-cyclohexenyl compound 4 (34 %) and the cis-fused dihydrobenzo[a]fluorene product 2 (45 %) containing a quaternary carbon (their structures were determined from their 1 H NOE spectra [10] ). Use of AgOTf and [PPh 3 AuCl]/AgOTf did not improve the chemoselectivity, with the formation of the additional cis-cyclohexenyl compound 3, which was inseparable from its trans isomer 4. Although use of HOTf (0.3 or 5 mol %) led to complete consumption of starting 1, we obtained only complex mixtures of unknown species.…”

“…[1] Gold complexes are prominent catalysts for activation of alkynes, allenes, and alkenes towards nucleophilic attack under ambient conditions. [2][3][4] Such nucleophilic enhancement enables gold catalysts to effect cycloadditions of novel types, including [4+2] or [3+2] enyne/ alkene cycloadditions [5] and [3+2] enyne/alkyne cycloadditions. [6] Recently, gold-activated cycloadditions of allene-ene functionalities have become particularly notable because they provide useful carbocyclic frameworks that are difficult to obtain by conventional methods.…”

“…[6] Recently, gold-activated cycloadditions of allene-ene functionalities have become particularly notable because they provide useful carbocyclic frameworks that are difficult to obtain by conventional methods. [7][8][9] Equations (1)(2)(3) show model gold-catalyzed [2+2] and [3+2] cycloadditions of allenes with tethered alkenes. [7][8][9] The versatility of such reactions is also reflected in a tandem reaction sequence involving an initial rearrangement of starting alkynyl acetates to allenyl acetates followed by [2+2] or [3+2] cycloaddition with tethered alkene components.…”

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…70 Mercury-and palladium-promoted ring expansion reactions of alkenylcyclobutanols are well investigated reactions triggered by release of strain in fourmembered ring systems. 71 These useful methodologies for the construction of five-membered ring systems have been successfully applied in the synthesis of natural products.…”