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An Alternative Mechanistic Paradigm for the β‐ Z Hydrosilylation of Terminal Alkynes: The Role of Acetone as a Silane Shuttle
Author(s) -
Iglesias Manuel,
Sanz Miguel Pablo J.,
Polo Victor,
FernándezAlvarez Francisco J.,
PérezTorrente Jesús J.,
Oro Luis A.
Publication year - 2013
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.201303063
Subject(s) - hydrosilylation , chemistry , moiety , vinylsilane , alkyne , silylation , silane , ligand (biochemistry) , nucleophile , heterolysis , medicinal chemistry , hydride , stereochemistry , photochemistry , metal , organic chemistry , catalysis , biochemistry , receptor
The β‐ Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I) 2 {κ‐C,C,O,O‐(bis‐NHC)}]BF 4 (M=Ir ( 3 a ), Rh ( 3 b ); bis‐NHC=methylenebis( N ‐2‐methoxyethyl)imidazole‐2‐ylidene) support a new mechanism, alternative to classical postulations, based on an outer‐sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R 3 SiO(CH 3 ) 2 ] + , which reacts with the corresponding alkyne in solution to give the silylation product [R 3 SiCHCR] + . Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R 3 SiCHCR] + affords selectively the β‐( Z )‐vinylsilane. The β‐ Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β‐( E )‐vinylsilanes.