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Interplay between Solvent and Counteranion Stabilization of Highly Unsaturated Rhodium( III ) Complexes: Facile Unsaturation‐Induced Dearomatization
Author(s) -
Gandelman Mark,
Konstantinovski Leonid,
Rozenberg Haim,
Milstein David
Publication year - 2003
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.200204457
Subject(s) - chemistry , rhodium , degree of unsaturation , medicinal chemistry , diethyl ether , photochemistry , solvent , ligand (biochemistry) , stereochemistry , polymer chemistry , organic chemistry , catalysis , biochemistry , receptor
Abstraction of the chloride ligand from the PCN‐based chloromethylrhodium complex 2 by AgX (X=BF 4 − , CF 3 SO 3 − ) or a direct C–C cleavage reaction of the PCN ligand 1 with [(coe) 2 Rh(solv) n ] + X − (coe=cyclooctene) lead to the formation of the coordinatively unsaturated rhodium( III ) complexes 3 . Compound 3 a (X = BF 4 − ) exhibits a unique medium effect; the metal center is stabilized by reversible coordination of the bulky counteranion or solvent as a function of temperature. Reaction of [(PCN)Rh(CH 3 )(Cl)] with AgBAr f in diethyl ether leads to an apparent rhodium( III ) 14‐electron complex 4 , which is stabilized by reversible, weak coordination of a solvent molecule. This complex coordinates donors as weak as diethyl ether and dichloromethane. Upon substitution of the BF 4 − ion in [(PCN)Rh(CH 3 )]BF 4 by the noncoordinating BAr f − ion in a noncoordinating medium, the resulting highly unsaturated intermediate undergoes a 1,2‐metal‐to‐carbon methyl shift, followed by β ‐hydrogen elimination, leading to the Rh‐stabilized methylene arenium complex 5 . This process represents a unique mild, dearomatization of the aromatic system induced by unsaturation.