Crystallographic characterization of a palladium(II) metallamacrocycle supported by an amino-functionalized ferrocene and its use as an efficient Suzuki-coupling catalyst

Abstract

Complexation of the bidentate ferrocenylamine [η-C 5H 4(CH 2)2N(CH 3)2]2Fe (1) with PdCl 2--(MeCN) 2 in MeOH at room temperature gives air-stable Pd 2Cl 4{Fe[η-C 5H 4(CH 2)2N(CH 3)2]}2 (2; yield 71%) of limited solubility in common organic solvents. X-ray single-crystal diffraction analyses showed that 2 has self-assembled into a metallamacrocyclic structure comprising two trans palladium(II) atoms intercalated with two eclipsed bis[(2-(dimethylamino)ethyl)- cyclopentadienyl]ferrocene groups, thus forming a {Pd 2Fe 2} heterometallic molecular "rectangle". Chloride abstraction with NH 4PF 6 leads to decomplexation, giving {[η-C 5H 4- (CH 2)2N(CH 3)2H] 2Fe}{PF 6}2 (3), which is the protonated form of 1. Complex 2 effectively catalyzes Suzuki cross-coupling reactions of aryl bromides with aryl boronic acids in MeOH at room temperature and 60°C, giving generally high yields even under low catalytic loads. The reaction conditions are reported together with comparison with other common catalysts.