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Phosphane‐Ligated Ionic Palladium Complexes: Synthesis, Characterization and Application as Efficient and Reusable Precatalysts for the Homogeneous Carbonylative Sonogashira Reaction under CuI‐Free Conditions
Author(s) -
Zhang Jing,
Wang Yongyong,
Zhao Xiaoli,
Liu Ye
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201301318
Subject(s) - chemistry , sonogashira coupling , phenylacetylene , ionic liquid , palladium , steric effects , carbonylation , aryl , catalysis , medicinal chemistry , ionic bonding , photochemistry , organic chemistry , carbon monoxide , ion , alkyl
The stable ionic Pd II complexes 1A – 4A were synthesized through the complexation of PdCl 2 (MeCN) 2 with the phosphane‐functionalized ionic liquids (FILs) 1 – 4 with π‐acceptor character. Single‐crystal X‐ray diffraction analyses showed that 1A – 4A were all composed of Pd II ‐centred square‐planar cations and triflate (OTf – , CF 3 SO 3 – ) counteranions. The complex cations in 1A – 3A possessed structural similarity to trans ‐PdCl 2 (PPh 3 ) 2 . The cation in 4A was a new Pd II ‐centered planar complex ligated by the phosphane–carbon anion–carbene (PCC) pincer in a tripodal manner. The stabilities of 1A – 4A were improved due to the intensive π‐backbonding interaction between the Pd and P atoms. When complexes 1A – 4A were used as precatalysts for homogeneous carbonylative Sonogashira coupling of PhI with phenylacetylene free of CuI, 1A – 3A exhibited excellent catalytic behaviour with a TON of up to 1700 at a CO pressure of 0.5 MPa and moderate temperature of 100 °C, whereas 4A exhibited poor activity towards the transformation of PhI due to the high stability of 4A . The recycling experiments of 3A in [Bpy]BF 4 (as a solvent) indicated that 3A could be recycled for 5 runs with neither activity loss nor metal leaching into the organic phase. Complex 3A also proved to be a general precatalyst for the carbonylative Sonogashira couplings of a wide range of aryl iodides with phenylacetylene. The selectivity of the desired carbonylation product depended more on electronic effects than the steric effects of the substituents of the aryl iodides.