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A Phosphinine‐Derived 1‐Phospha‐7‐Bora‐Norbornadiene: Frustrated Lewis Pair Type Activation of Triple Bonds
Author(s) -
Leitl Julia,
Jupp Andrew R.,
Habraken Evi R. M.,
Streitferdt Verena,
Coburger Peter,
Scott Daniel J.,
Gschwind Ruth M.,
Müller Christian,
Slootweg J. Chris,
Wolf Robert
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202000266
Subject(s) - norbornadiene , frustrated lewis pair , chemistry , triple bond , borane , metathesis , medicinal chemistry , boranes , bond cleavage , alkyne , adduct , lewis acids and bases , stereochemistry , nitrile , photochemistry , boron , double bond , polymer chemistry , organic chemistry , catalysis , polymer , polymerization
Salt metathesis of 1‐methyl‐2,4,6‐triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1‐phospha‐7‐bora‐norbornadiene derivative 2 . The C≡N triple bonds of nitriles insert into the P−B bond of 2 with concomitant C−B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ 4 ‐phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus–boron bond in 2 , which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P−B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4‐addition.