Zero-valent Palladium Complex Effective for the Copper-free Sonogashira Coupling

Bis[di-tert-butyl(4-dimethylaminophenyl)phosphine]palladium(0) (1) is a zero valent palladium complex consisted of electron donating phosphine ligands and is effective for oxidative addition to less reactive chlorobenzene derivatives. 1 can be also used as a catalyst for a copper-free Sonogashira coupling. In the presence of a catalytic amount of 1, the Sonogashira coupling proceeds by the treatment of terminal alkynes with chloro aryl/heteroaryl compounds without using copper salts. Also, the feature of 1 is that the P-Pd-P bond angle is bent in 174.7 degrees which was revealed by X-ray crystal structure analysis. Furthermore, this result indicates that the bent structure affects the catalytic activity of 1 from the comparison with other complexes. In this way, 1 shows high reactivity for cross coupling reactions as a catalyst and is expected to be used in organic synthesis.