| 19035583 |
Liao CY, Chan KT, Tu CY, Chang YW, Hu CH, Lee HM: Robust and electron-rich cis-palladium (II) complexes with phosphine and carbene ligands as catalytic precursors in Suzuki coupling reactions. Chemistry. 2009;15(2):405-17.
A new imidazolinium ligand precursor [L (2) H] Cl (2) was prepared in 86 % yield. Compared with its imidazolium counterpart, [L (1) H] Cl (1), 2 is very sensitive to moisture and can undergo ring-opening reactions very readily. Palladium complexes with the ring-opened products from imidazolinium salts were isolated and characterized by X-ray crystallography. Theoretical studies confirmed that the imidazolinium salt has a higher propensity for the ring-opening reaction than the imidazolium counterpart. New mixed phosphine/carbene palladium complexes, cis-[PdCl (2)(L)(PR (3))] (L=L (1) and L (2); R=Ph, Cy), were successfully prepared. These complexes are highly robust as revealed by variable-temperature NMR spectroscopic studies and thermal gravimetric analysis. The structural and electronic properties of the new complexes on varying the carbene group (imidazol-2-ylidene group (unsaturated carbene) vs. imidazolin-2-ylidene (saturated carbene)) and the phosphine group (PPh (3) vs. PCy (3)) were studied in detail by X-ray crystallography, X-ray photoelectron spectroscopy, and theoretical calculations. The catalytic study reveals that cis-[PdCl (2)(L (2))(PCy (3))] is a competent Pd (II) precatalyst for Suzuki coupling reactions, in which unreactive aryl chlorides can be applied as substrates. |
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