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Efficient Addition Reaction of Dibutylphosphane Oxide with Alkynes: New Mechanistic Proposal Involving a Duo of Palladium and Brønsted Acid
Author(s) -
Kanada Jun,
Tanaka Masato
Publication year - 2011
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201000758
Subject(s) - chemistry , brønsted–lowry acid–base theory , catalysis , palladium , denticity , medicinal chemistry , moiety , yield (engineering) , regioselectivity , ligand (biochemistry) , chelation , stereochemistry , organic chemistry , metal , biochemistry , materials science , receptor , metallurgy
The addition reaction of dibutylphosphane oxide [Bu 2 P(O)H] with alkynes proceeds efficiently in the presence of palladium‐chelating phosphane–Brønsted acid catalyst systems. Terminal alkynes afford branched‐structured products selectively. On the other hand, the same reaction using monodentate phosphane ligands or the reaction run in the absence of a Brønsted acid affords a much lower yield. A mechanistic study has revealed that Brønsted acids (XOH) interact with oxygen in MP(O)R 2 species (M=Pd, Pt) through hydrogen bonding to transform them to ionic M + ←PR 2 (OH⋅⋅⋅O − X) species, which was confirmed by NMR spectroscopy and X‐ray crystallography. The phosphane‐like PR 2 (OH⋅⋅⋅O − X) moiety is coordinatively labile, as substantiated by the ligand exchange reaction with tert ‐butyl isocyanide. A new mechanism that accommodates these observations has been proposed to rationalize the enhancement of catalytic activity and the regioselectivity induced by the Brønsted acid.