The Autocatalytic Isomerization of Allylbenzene by Nickel(0) Tetrakis(triethylphosphite)

Abstract

Using [Ni{(POEt)3}4] as catalyst precursor for the catalytic isomerization of allylbenzene to beta‐methylstyrene, time‐course studies suggest a mechanism that is consistent with an autocatalytic reaction. The sigmoidal curve observed when plotting conversion vs. time fits exceptionally well to a kinetic model of an autocatalytic process (R2 = 0.998). We show that the uncoordinated phosphite, generated during the catalyst activation, reduces the acid concentration and, consequently, has a detrimental effect on the formation of the protonated active nickel catalyst. The nickel complex protonation is seen as a key step in forming the active catalytic species. The novel use of a mercury salt as a phosphite scavenger leads to inhibition of the free phosphite's capability to lower acid concentration, improving the catalytic performance of the system, consistent with the mechanism proposed.

Neues Mitglied der Deutschen Akademie der Naturforscher Leopoldina: Michael Sattler / Australian Museum Eureka Prizes: T. Maschmeyer und E. J. New / Alfred C. Egerton Gold Medal: K. Kohse‐Höinghaus

“…Maschmeyer forscht auf den Gebieten Katalyse, nachhaltige Prozesse, erneuerbare Rohstoffe, ionische Flüssigkeiten, mikro‐ und mesoporöse nanostrukturierte Materialien sowie reversible Energiespeichereinheiten. Er beschrieb in der Angewandten Chemie die Charakterisierung polymerer Kohlenstoffnitrid‐Photokatalysatoren, und sein Beitrag über [Ni{(POEt) 3 } 4 ] in der katalytischen Isomerisierung von Allylbenzol wurde zum Titelbild des European Journal of Inorganic Chemistry gewählt . Maschmeyer ist Mitglied der internationalen Beiräte von ChemCatChem , ChemPlusChem und der Zeitschrift für allgemeine und anorganische Chemie .…”

Elected to the Deutsche Akademie der Naturforscher Leopoldina: M. Sattler / Australian Museum Eureka Prizes: T. Maschmeyer and E. J. New / Alfred C. Egerton Gold Medal: K. Kohse‐Höinghaus

“…Maschmeyer's research interests include catalysis, sustainable processes, renewable feedstocks, ionic liquids, micro‐ and mesoporous nanostructured materials, and reversible energy‐storage devices. He has reported in Angewandte Chemie on the characterization of polymeric carbon nitride photocatalysts, and his report on the use of [Ni{(POEt) 3 } 4 ] in the catalytic isomerization of allylbenzene was featured on the cover of the European Journal of Inorganic Chemistry . Maschmeyer is on the International Advisory Boards of ChemCatChem , ChemPlusChem , and the Zeitschrift für allgemeine und anorganische Chemie .…”

Modular Ni(0)/Silane Catalytic System for the Isomerization of Alkenes

“…Transition metal-catalyzed isomerization reactions typically proceed via one of three possible mechanisms: (i) radical pathway, ,,, (ii) π-allyl pathway, or (iii) insertion/elimination via a metal hydride (Figure a). Nickel catalysts are particularly attractive not only because Ni is an Earth-abundant, first-row transition metal but also because they are mechanistically versatile (i.e., able to proceed through 1-electron and 2-electron pathways). ,− Ni has been proposed to isomerize alkenes through insertion/elimination, − radical, and π-allyl-type ,,, mechanisms. The insertion/elimination pathway using a Ni–H catalyst is particularly attractive because it is the proposed mechanism for many chain walking applications. ,,,− Elucidation of the active species structure and the effect of ancillary ligands has been specifically identified as the major challenge in Ni-catalyzed remote functionalization reactions .…”

“…Previous work has accessed Ni–H species in situ (Figure b) for alkene isomerization and remote functionalization by oxidative addition of strong acids [e.g., H 2 SO 4 , ,,, HCl, HBF 4 , and HN­(SO 2 CF 3 ) 2 or polar O–H bonds , ], oxidative addition of alkyl halides followed by β-hydride elimination, or reduction of Ni­(II) with additives that can limit functional group tolerance (e.g., Grignard reagents, , NaBH 4 , − LiAlH 4 , LiBHEt 3 , ,, SnCl 2 , and MAO). In remote functionalization applications, the use of Ni–X (X = halide) complexes in conjunction with a silane as the H-source by the Zhu lab ,,, and others ,, has achieved efficient and selective reactivity for the remote functionalization of alkenes.…”