@misc{oai:ir.soken.ac.jp:00003102,
 author = {武藤, 翼 and ムトウ, ツバサ and MUTO, Tsubasa},
 month = {2016-02-17},
 note = {  The self-assembling construction of potentially functionalized, highly-ordered molecular architectures via non-covalent interactions among the monomer units is rapidly generating interest from a wide range of chemists.  In particular, it has been reported that organic molecules having rigid planar backbones with both hydrophobic and hydrophilic side chains often form bilayer assemblages.  If hydrophobic and hydrophilic side chains are incorporated onto the planar NCN palladium pincer backbone, the amphiphilic palladium pincer complexes would adopt a self-assembled architecture having catalytic activity.  The author reports the design, preparation, and self-assembling vesicle formation of amphiphilic palladium pincer complexes and their application to the C-C bond forming reactions in water.
  The pincer palladium complexes 1 and 2 having pairs of hydrophobic dodecyl chains and hydrophilic tri(ethylene glycol) (TEG) chains, located opposite to one another on the rigid planar backbone, were designed for use in the self-assembly formation of vesicles exhibiting catalytic activity in water (Figure 1).  These amphiphilic pincer palladium complexes were prepared from their 2,6-diformyl precursors 3 and 4 and primary anilines 5 and 6, respectively, via the ligand introduction route which was previously developed by Uozumi and co-workers (Scheme 1).
  With the amphiphilic pincer palladium complexes 1 and 2 in hand, the author next turned his attention to demonstrating their self-assembling potential.  After thorough screening, the author was pleased to find that both complexes 1 and 2 exhibited good assembling potential under aqueous conditions.  The amphiphilic pincer complex 1 was treated in water at 60 °C for 4 h, and the resulting aqueous mixture was cooled to ambient temperature and vortexed to afford an aqueous slurry of 1vscl.  A dynamic light scattering (DLS) study of the slurry demonstrated the formation of the vesicle 1vscl (average diameter of 550 nm).  To an acetonitrile solution of 2 was added water (H2O/CH3CN = 9/1) and the resulting aqueous mixture was concentrated at 80 °C for 6 h, during which time acetonitrile was slowly vaporized, to afford a pale yellow aqueous suspension.  The resulting suspension was cooled and centrifuged (4000 rpm, 15 min) to give precipitates.  The precipitates were suspended in water and studied by DLS to demonstrate that the vesicle 2vscl having an average diameter of 463 nm was formed.
  In order to determine the morphologies of bilayer vesicles of 1vscl and 2vscl, the author performed atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analyses.  AFM and SEM analyses revealed the spherical morphologies of 1vscl and 2vscl [figure 2(a) and (b) and Figure 3(a) and (b), respectively].  TEM observation of vesicular composites 1vscl and 2vscl showed that these composites were hollow structures and the thicknesses of both the vesicle membranes were observed to be ca. 6–7 nm [Figure 4(a) and (b)].  These data are consistent with those of the bilayer membranous structures of 1 and 2 each having both monomer lengths of ca. 2.8 nm in their structures. 
  The incorporation of the fluorescent reagent, fluorescein, into 1vscl revealed a hollow structure with an inner hydrophobic region in the membrane.  Thus, when the isolated 1vscl was exposed to fluorescein under aqueous conditions, the fluorescent vesicles, 1vscl/fluorescein, were obtained [Figure 5(a) and Figure 6(a)].  A similar hollow structure of 2vscl was also observed microscopically with the same fluorescence reagent [Figure 5(b) and Figure 6(b)].  
  These experiments demonstrated that the structure of the vesicle 1vscl was similar to that of 2vscl.  Therefore, the inversion of the positions of hydrophobic and hydrophilic groups on the pincer backbone did not strongly influence vesicle formation via self-assembly of 1 and 2.
  The author next estimated the detailed membranous structure of the vesicle 1vscl using molecular dynamics simulation.  Initial molecular structure of the complex 1 was determined by ab initio calculation.  The molecular dynamics simulation of the bilayer membranous structure of the vesicle 1vscl, which was constructed by 128 molecules of the complex 1 in a basic cell, was carried out in the NPT ensemble at 298.15 K under 1 atm (figure 7).  This simulation also supported the formation of the bilayer membranous structure. The thickness of the calculated membrane was ca. 6.2 nm and was in good agreement with the observed thickness in TEM analysis.
  With the desired vesicles 1vscl and 2vscl in hand, the author next explored their catalytic potential for the Miyaura–Michael reaction of 2-cyclohexene-1-one (7) with sodium tetraphenylborate (8).  Significant acceleration of the Miyaura–Michael reaction in water was observed by the formation of vesicles.  Thus, the vesicle 1vscl (2 mol% Pd) promoted the Miyaura–Michael reaction of 7 with 8 in water to give the desired arylated product 9 in 83% yield in 12 h with 98% reaction selectivity.  In contrast, only a 7% yield of the arylated product 9 was obtained when monomer 1 was used as the catalyst.  The reaction of 7 with 8 proceeded in the presence of vesicle 2vscl to provide 9 in 19% yield with >99% reaction selectivity, whereas monomer 2 afforded only a 5% yield of 9 with much lower selectivity.  Thus, only slight promotion of the Miyaura-Michael reaction in water was observed by the self-assembling of 2.  These results revealed that the construction of self-assembled vesicles is required for the efficient catalysis of the Miyaura–Michael reaction in water.  In addition, the catalytic activity of the vesicle 1vscl bearing hydrophilic tri(ethylene glycol) chains close to the palladium center is higher than that of the vesicle 2vscl bearing hydrophobic dodecyl chains close to the palladium center.  
  The vesicle 1vscl was also effective for the arylating oxirane ring opening reaction of vinyl epoxide 10 with phenylboronic acid (11) to give an 84% yield of the arylated product 12 along with its regioisomer 13 (Scheme 3).   However, under similar reaction conditions, the reaction with the monomer 1 did not proceed as efficiently.
  In summary, the author has designed and prepared two amphiphilic pincer palladium complexes bearing hydrophobic or hydrophilic side chains.  The prepared complexes were self-assembled in aqueous media to provide bilayer vesicles which were characterized by DLS, various microscopic techniques, and theoretical calculation.  The catalytic performances of the obtained vesicles 1vscl and 2vscl are superior to that of the monomeric complexes 1 and 2 for the Miyaura–Michael reaction in water.  In addition, the catalytic activity of the vesicle 1vscl is much higher than that of the vesicle 2vscl.  The similar enhancement of the catalytic performance of the vesicle 1vscl was also observed in the arylating oxirane ring opening reaction in water., 総研大甲第1476号},
 title = {両親媒性ピンサー型パラジウム錯体から成るベシクル触媒の創製と水中有機分子変換反応への応用},
 year = {}
}