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Copper-Phosphido Intermediates in Cu(IPr)-Catalyzed Synthesis of 1-Phosphapyracenes via Tandem Alkylation/Arylation of Primary Phosphines

Lookup NU author(s): Connor Sibbald, James Fleming, Dr Lee HighamORCiD

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Chemical Society, 2018.

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Abstract

© 2018 American Chemical Society. Tandem alkylation/arylation of primary phosphines PH2R (R = Ph, Cy, Fc, FcCH2; Fc = ferrocenyl) with 5-bromo-6-chloromethylacenaphthene (1) and 2 equiv of NaOSiMe3 using the catalyst precursor Cu(IPr)(Cl) gave a series of 1-phosphapyracenes (R-PyraPhos, 2a-d), which were isolated as borane adducts 3a-d. Similar reactions of the chiral air-stable primary phosphines PH2Ar∗ (Ar∗ = (S)-binaphthyl (4), (R)-MeO-binaphthyl (5)) to yield 2e,f and 3e,f were diastereoselective (dr = 2:1 and 1.2:1, respectively), and chromatography gave a highly enriched sample of one diastereomer of 3f. The mechanism of catalysis was investigated by NMR monitoring and independent syntheses of potential intermediates. The phosphido complexes Cu(IPr)(PHAr′) (Ar′ = Ph, (R)-MeO-binaphthyl) were generated in equilibrium mixtures, along with Me3SiOH, from Cu(IPr)(OSiMe3) and PH2Ar′. They reacted with benzyl chloride 1 to yield Cu(IPr)(Cl) and the secondary phosphines PHAr′(CH2Ar) (Ar = Br-acenaphthyl); addition of NaOSiMe3 yielded PyraPhos derivatives 2a,f. Deprotonation of the cations [Cu(IPr)(PHAr′CH2Ar)][OTf] (Ar′ = Ph, (R)-MeO-binaphthyl) was investigated as a route to the secondary phosphido complexes Cu(IPr)(PAr′CH2Ar) (13). We propose that C-Br oxidative addition in the Cu(I)-phosphido intermediates 13 followed by P-C reductive elimination from Cu(III)-phosphido complexes forms the PyraPhos ring, with diastereoselection arising from rapid pyramidal inversion of Cu-phosphido groups.

Publication metadata

Author(s): Wang G, Gibbons SK, Glueck DS, Sibbald C, Fleming JT, Higham LJ, Rheingold AL

Publication type: Article

Publication status: Published

Journal: Organometallics

Year: 2018

Volume: 37

Issue: 11

Pages: 1760-1772

Print publication date: 11/06/2018

Online publication date: 23/05/2018

Acceptance date: 05/04/2018

Date deposited: 22/05/2020

ISSN (print): 0276-7333

ISSN (electronic): 1520-6041

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.organomet.8b00198

DOI: 10.1021/acs.organomet.8b00198

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