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Palladium‐Catalyzed Reactions in Industry, 4[ ]. Synthesis of New Palladium Catalysts: First Isolation and Characterization of all Intermediates in a Cyclopalladation Reaction
Author(s) -
Beller Matthias,
Riermeier Thomas H.,
Haber Steffen,
Kleiner HansJerg,
Herrmann Wolfgang A.
Publication year - 1996
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19961291018
Subject(s) - chemistry , palladium , metalation , reactivity (psychology) , catalysis , stereoselectivity , coupling reaction , metal , metallacycle , monomer , medicinal chemistry , combinatorial chemistry , stereochemistry , organic chemistry , polymer , x ray crystallography , medicine , optics , alternative medicine , physics , pathology , diffraction
In order to synthesize chiral palladacycles for stereoselective C–C coupling reactions we studied the cyclopalladation of P‐chiral phosphanes 2 and 3 . New palladium complexes of the type L 2 PdX 2 ( 6, 8 ) and LXPd–μ‐X 2 –PdXL ( 5, 9 , X = Cl; L = 2, 3 ) were isolated. A detailed study of the reactivity of all intermediates towards cyclopalladation proved the mechanism of cyclometalation reactions of o ‐tolylphosphanes for the first time. Different deuteration experiments clearly demonstrated the higher reactivity of dimeric palladium complexes towards metalation compared to monomeric species. In agreement with this observation only 5 and 9 gave the cyclopalladated products 4 and 10 as revealed by FAB mass spectrometric investigations. Under the described reaction conditions the synthesis of the corresponding palladacycles 4, 10 is not possible because cyclometalation is a reversible process with LXPd–μ–X 2 –PdXL as thermodynamic more stable products. The results demonstrate the importance of free coordination sites on the metal atom for cyclometalation reactions or more general CH activation processes.