Enhancing Electrophilic Alkene Activation by Increasing the Positive Net Charge in Transition‐Metal Complexes and Application in Homogeneous Catalysis

Abstract

Among a large variety of fine-tuning parameters for homogeneous catalysts the net charge of transition-metal complexes appear to be an interesting factor that considerably affects activation of substrates and catalytic activity in general. The electrophilicity of coordinated alkenes in transition-metal complexes can be strongly enhanced by increasing the positive net charge, resulting in strong carbocationic properties. Theoretical and experimental studies have shown that the alkene in cationic complexes is kinetically and thermodynamically more activated towards nucleophilic addition than in neutral complexes. The concept of increasing the positive complex charge is thought to be useful for the development of new catalysts for reactions in which alkenes or other unsaturated substrates are involved.

Hydroamination reactions by metal triflates: Brønsted acid vs. metal catalysis?

“…[10][11][12] In both of these routes, the turnover step requires the protonolysis of the alkyl-M bond. For most addition of nucleophilic primary or secondary alkylamines and anilines, reaction mechanisms are fairly well established, including the 60 isolation of catalytically-viable intermediates, theoretical studies 13 and enantioselective examples, which have been described in a previous Perspective. 14 Scheme 2 General mechanisms for metal-catalysed hydroamination 65 reactions (illustrated for intramolecular reactions).…”

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.…”

Elektrophile Aktivierung von Alkenen mit Platin(II): sehr viel mehr als eine langsame Variante von Palladium(II)

“…[20] Ein ganz entscheidender Befund stammte von Panunzi et al, [21] die zeigen konnten, dass die Addition von Diethylamin an einen diastereomerenreinen Platinkomplex des prochiralen Olefins 1-Buten nach Protonolyse ausschließlich das (S)-N,N'-Diethyl-sec-butylamin (das Produkt der Markownikoff-Addition mit anti-Konfiguration) liefert [Gl. (3)]. …”

“…Wo es uns angebracht erscheint, werden wir Vergleiche mit verwandten Palladium-katalysierten Prozessen anstellen. Stöchiometri-sche Olefinaktivierungen mit Pt-Reagentien wurden in einem neueren Übersichtsartikel zusammengefasst, [3] und wir stellen nur einige ausgewählte Beispiele vor. Die verwandten Ptkatalysierten Aktivierungen von Alkinen, z.…”