Palladacycle from Cyclometalation of the Unsubstituted Cyclopentadienyl Ring in Ferrocene: Synthesis, Characterization, Theoretical Studies, and Application to Suzuki鈥揗iyaura Reaction
文摘
The ferrocenylimines of general formula [(畏5-C5H5)Fe(畏5-C5H4)-CH2N鈺怌H-C(R)鈺怌H-C6H5] with R = H (2a) and CH3 (2b) were conveniently prepared from ferrocenylmethylamine. Reaction of 2a,b with lithium tetrachloropalladate in methanol in the presence of anhydrous sodium acetate resulted in the formation of the di-渭-chloro-bridged heteroannular cyclopalladated complexes 3a,b via the unsubstituted ferrocenyl C鈥揌 bond activation of the related ligands. Treatment of 3a,b with triphenylphosphine gave Pd{[(畏5-C5H4)Fe(畏5-C5H4)CH2N鈺怌H-CH鈺怌H-C6H5]}ClPPh3 (4a) and Pd{[(畏5-C5H4)Fe(畏5-C5H4)-CH2N鈺怌H-C(CH3)鈺怌H-C6H5]}ClPPh3 (4b), respectively. The crystal structures of 4a,b confirmed the formation of a carbon鈥損alladium bond by using a carbon atom in the unsubstituted cyclopentadienyl ring. Additionally, theoretical studies using density functional theory calculations were carried out in order to account for the regioselectivity of cyclometalation. As for the catalysts, using 0.1% of palladacycles 4a,b in the presence of K3PO4路7H2O as base exhibited excellent yields in the Suzuki鈥揗iyaura coupling reaction of aryl bromides with phenylboronic acid.