Palladium‐Catalyzed Reactions in Industry, 4[]. Synthesis of New Palladium Catalysts: First Isolation and Characterization of all Intermediates in a Cyclopalladation Reaction

Abstract

Abstract 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.