PALLADIUM-CATALYZED REACTIONS IN INDUSTRY .4. SYNTHESIS OF NEW PALLADIUM CATALYSTS - FIRST ISOLATION AND CHARACTERIZATION OF ALL INTERMEDIATES IN A CYCLOPALLADATION REACTION

In order to synthesize chiral palladacycles for stereoselective C-C co upling reactions we studied the cyclopalladation of P-chiral phosphane s 2 and 3. New palladium complexes of the type L(2)PdX(2) (6, 8) and L XPd-mu-X(2)-PdXL (5, 9, X = Cl; L = 2, 3) were isolated. A detailed st udy of the reactivity of all intermediates towards cyclopalladation pr oved the mechanism of cyclometalation reactions of o-tolylphosphanes f or the first time. Different deuteration experiments clearly demonstra ted the higher reactivity of dimeric palladium complexes towards metal ation compared to monomeric species. In agreement with this observatio n 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 Me corresponding palladacycles 4, 10 is n ot possible because cyclometalation is a reversible process with LXPd- mu-X(2)-PdXL as thermodynamic more stable products. The results demons trate the importance of free coordination sites on the metal atom for cyclometalation reactions or more general CH activation processes.