Phosphines, aryl, coupling constants

Table 2.6 Jp. coupling constants (P-Ph) of representative aryl phosphines [Hz]...

Aryl exchange occurs before transmetallation. Thus, the transmetal-lation rate constant which is low for steric and electronic reasons results in increasing the coupling product of phosphine-bound aryls (Eq. 51). Transmetallation is slowed down when electron-rich haloarenes and weak bases are used and accelerated with electron-deficient haloarenes because the transmetallation shown in Eqs. 16 and 17 involves nucleophilic substitution of Pd-X. The reported equilibrium ratio of 3/5 is 4/96 at 60 °C when Ar is p-methoxyphenyl. Thus, it is quite reasonable that the reaction accompanies a large amount of 6 when the rate constant of transmetallation ifej is lower than ky A strong base, polar solvent, and a sterically less hindered bidentate ligand, such as dppf, increase k. The formation of yields of 9 in p-iodoanisole higher than the bromo derivative... 

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