Synthesis Of Phosphinite PCN Pincer Pd(II) Complexes And Their Application In Catalysis

Trident pincer-type transition metal complexes, which contain a central aryl ring with two ortho-substituted donor groups, have played an important role in organometallic synthesis and catalysis since Shaw's pioneering work. Their steric and electronic features can be modified at the donor sites as well as the metal sites which may give rise to excellent stability and/or activity. Research in this chemistry has been dominated by various symmetrical pincer complexes consisting of two identical donors at the two ortho-positions, such as PCP and NCN types. However, reports on the unsymmetrical ones are relatively few, Esp. those on unsymmetrical chiral pincer metal complexes are rather limited. In this thesis, we described the synthesis, characterization and catalytic application of novel PCN type chiral and achiral iminophosphinite, together with chiral imidazolinylphosohinite pincer palladium complexes.1. Synthesis and characterization of unsymmetrical achiral and chiral iminophosphinite PCN pincer Pd (Ⅱ) complexesA series of novel PCN pincer palladium (Ⅱ) complexes were readily prepared in two steps, namely the condensation of m-hydroxybenzaldehyde with achiral or chiral amine and then one-pot phosphorylation/palladation reaction. Namely, la-d reacted with diphenylchlorophosphine or diisopropylchlorophosphine in the presence of triethylamine in refluxing toluene, followed by the addition of palladium chloride to obtain the corresponding PCN pincer Pd (Ⅱ) complexes 2a-e. All compounds were characterized by 1H NMR,13C NMR, IR,31P NMR and HRMS spectra, with the molecular structures of 2b further determined by X-ray single-crystal diffraction. 2. Synthesis and characterizaiton of unsymmetrical chiral imidazolinyl-phosphinite PCN pincer Pd (Ⅱ) complexesThe required chiral imidazolinyl-containing m-phenol derivatives 4a-e were prepared in a four-step sequence from commercially available m-hydroxybenzoic acid. With the expected ligand precursors in hand, the one-pot phosphorylation/metalation reaction was carried out to afford complexes 5a-f. Then, the palladium-chloride complex 5e was readily converted to the corresponding iodide derivative 6e. All the compounds were characterized by 1H NMR,13C NMR, DEPT,31P NMR, HSQC, HMBC and IR spectra, with the molecular structures of 5a-f,6e further determined by X-ray single-crystal diffraction and elemental analysis. 3. Application of iminophosphinite PCN pincer Pd (Ⅱ) complexes in the Suzuki reactions.PCN pincer Pd complexes were successfully applied to Suzuki reaction. The best results were obtained using K3PO4·7H2O as the base in EtOH 10 h with a catalyst loading of 0.3 mol%, even at a relative low temperature of 50℃. Then, series of aryl bromides were tested under the optimized conditions. Furthermore, the difference of catalytic activity of related PCP, NCN and PCN pincer complexes was also discussed. 4. Application of chiral imidazolinylphosphinite PCN pincer Pd (Ⅱ) complexes in the Suzuki cross-coupling reaction.The catalytic activities of PCN pincer Pd complexes in the Suzuki reaction, especially in the asymmetric Suzuki cross-coupling, were investigated. The pincer complexes were shown to be active catalysts with moderate enantioselectives for asymmetric Suzuki reactions.5. Applications of PCN pincer Pd (Ⅱ) complexes in the Sonogashira and domino Sonogashira reactions.The PCN pincer Pd complex 2a-e was shown to be the highly efficient catalyst in the Sonogashira. The optimized conditions were obtained using the Cs2CO3 as the base in methanol at 70℃, affording the products in moderate to good yields with 1 mol% catalyst loading. Likewise, the catalytic activities of NCN, PCP and PCN complexes were discussed in detail to get more comprehensive results. In addition, the pincer complexes could also promote the domino Sonogashira reactions.