Addition reactions of mononuclear η3-allenyl/propargyl transition metal complexes: a new class of potent organometallic carbon electrophiles
Resource
Coordination Chemistry Reviewss 190-192: 1143-1168
Journal
Coordination Chemistry Reviews
Pages
1143-1168
Date Issued
1999
Date
1999
Author(s)
Chen, Jwu-Ting
Abstract
The cationic mononuclear η3-allenyl/propargyl complexes exhibit new non-classical organometallic bonding of σ,π-mode and remarkable activity of potent carbon electrophiles. The organic moieties of the title species, general formula R'R''CCCR, use all three adjacent unsaturated carbons to bond with metal in a unique coplanar manner. The C3 skeletons thus are severely distorted from the normal linear configuration to 150 ± 5°. The R'R''C-C distances are in the range of long double bonds; whereas C-CR are between double and triple bonds, indicating the resonance structures of allenyl and propargyl. The cationic complexes with η3-allenyl/propargyl ligands can undergo feasible reactions of regioselective nucleophilic addition which provide a pragmatic synthetic access to new organometallic species of central-carbon-substituted η3-allyl, η3-oxa- and η3-aza-trimethylenemethane. The broad spectrum of C-Nu bond formation encompasses hydroxylation, alkoxylation, phenoxylation, acyloxylation, thioxylation, thio- and seleno-phenoxylation, amination, amidation, phosphination, etc. As to carbation, the η3-allenyl/propargyl complexes react with carbanions to form η3-trimethylenemethane complexes. The electrophilicity of η3-C3H3 allows us to conduct regioselective carbon-carbon coupling with the electron-rich aromatics to achieve aromatic electrophilic substitution. Although both η3-allenyl/propargyl and η1-allenyl complexes are essentially subject to similar nucleophilic addition, the former are distinctly more reactive and versatile. From the mechanistic viewpoint, the cationic η3-allenyl/propargyl complexes prefer to undergo external nucleophilic attack at the central carbon. In contrast, nucleophilic addition to the η1-allenyl complexes requires preceding coordination of the nucleophile to a metal. (C) 1999 Elsevier Science S.A.
Type
journal article
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