73. Wang, G.; Gibbons, S. K.; Glueck, D. S.;
Sibbald, C.; Fleming, J. T.; Higham, L. J.; Rheingold, A. L.
Copper–Phosphido Intermediates in Cu(IPr)-Catalyzed
Synthesis of 1-Phosphapyracenes via Tandem
Alkylation/Arylation of Primary Phosphines. Organometallics2018, 37, 1760–1772.
Abstract
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.
