Cyclopalladated Ferrocenylimines Complexes: Synthesis, Characterization And Application In C-C And C-N Coupling Reactions

In this thesis, the synthesis, characterization and crystal structures of a series of newpyridine adducts, tricyclohexylphosphine adducts and monophosphinobiaryl ligand(DCPAB, DCPB) adducts of dimeric cyclopalladated ferrocenylimines were reported.These complexes have been successfully used in palladium-catalyzed C-C and C-Nbond forming reactions of aryl bromides and aryl chlorides.1. Five new pyridine-cyclopalladated ferrocenylimine complexes 1-5 have been easilyprepared (Schemel) and well characterized by elemental analysis, ESI-MS, ¹H NMRand IR spectra. Their detailed structures are determined by single-crystal X-rayanalysis. To the best of our knowledge, the crystal structures of all monomeric imineand amine-based palladacycles indicate that, in the solid state, the trans isomercrystallizes preferentially. Surprisingly, the single crystal X-ray analysis of complex 2and 5 revealed cis-configuration of coordinated pyridine to the imino nitrogen in thesolid state, while 1, 3 and 4 are trans complexes. These complexes were found to beefficient for the Suzuki reaction of aryl bromides with phenylboronic acid. Typically,using 0.2 mol% of 1 in the presence of 1.5 equivalent of K₂CO₃ as base in toluene at100℃could provide the coupled products in good to excellent yields.2. A series of new tricyclohexylphosphine(PCy₃)-cyclopalladated ferrocenyliminescomplexes 6-11 have been easily synthesized (Scheme 2). The synthesis andcharacterization of a new 1,1'-bisferrocenylimine [{(η⁵-C₅H₄)-CH=NCy}₂Fe] 12 and its monocyclopalladated derivative 14 were also reported (Scheme 3). The compound14 was found to be [PdCl{[(η⁵-C₅H₄)-CHO]Fe[(η⁵-C₅H₃)-CH=NCy]}(PCy₃)], whichwas obtained from the reaction of 12 with equimolar amounts of Li₂PdCl₄/NaOAc inmethanol at room temperature and subsequent treatment of the resulting product withtricyclohexylphosphine (PCy₃). The detailed structures of seven new palladacycleshave been determined by single-crystal X-ray analysis. The use of these palladacycles6-10 and 14 as catalysts for Suzuki and Heck reactions was examined. They werefound to be very efficient for the Suzuki reaction of aryl chlorides with phenylboronicacid. Typically, using 0.1 mol% of catalyst in the presence of 1.5 equivalent ofCs₂CO₃ as base in dioxane at 100℃provided coupled products in excellent yields.These complexes also displayed good activity in the Heck reaction of a range of arylbromides with acrylic acid ethyl ester although they were not particularly useful forthe activation of aryl chlorides.3. One-pot synthesis of symmetrical biaryls via the coupling of bis(pinacolato)-diboron with aryl chlorides catalyzed by tricyclohexylphosphine-cyclopalladatedferrocenylimine complexes has been described (Scheme 4). These complexes werehighly effective catalysts and the typical catalytic loadings were 0.5-1mol%, whichwere rather low compared to the value of 4 mol% in the PdCl₂(dppf) catalyzedcoupling of aryl bromides. The corresponding symmetrical biaryls were isolated in good to high yields.4. A series of new monophosphinobiaryl ligand (DCPB and DCPAB)-cyclopalladatedferrocenylimines complexes 16-25 have been easily synthesized (Scheme 5). Thedetailed structures of six new palladacycles 16-17, 20, 22-23, 25 have beendetermined by single-crystal X-ray analysis. The cyclopalladated ferrocenyliminecomplex 17 was found to be a highly active one-component precatalyst for theamination of aryl chlorides in water in the presence of inexpensive KOH and t-BuOHas base and an additive, respectively (Scheme 6). The ¹H NMR spectra of 22 and 23indicated that they were mixtures of isomers in solution since the signals in N- phenyland Cp ring region appeared in pairs. This kind of isomerism might be caused by thesteric hindrance between the ortho-substituted chlorine in the N-phenyl ring andα-methyl group. The single crystal X-ray analysis of complex 22 revealed an anti,trans-configuration in the solid state, while 23 is syn, trans complex.5. The use of tricyclohexylphosphine(PCy₃)-cyclopalladated ferrocenylimine complex6 as catalyst forα-arylation of acetylferrocene and aromatic halide was examined (Scheme 7). It was found that the products were different from those of literature. Theα-arylation of acetylferrocene and aromatic halide catalyzed by monophosphinobiarylligand (DCPAB)-cyclopalladated ferrocenylimine complex 25 has also been described(Scheme 8), giving the diarylated products.