A New Palladium Complex:the Synthesis And Initiation Of Isocyanide Polymerization Discussion

A family of air-stable (phenylbuta-1,3-diynyl)-palladium(II) complexes and phenylethynyl-palladium(II) complexes were designed and prepared through a facile synthetic procedure. These Pd complexes were revealed to initiate the polymerization of phenyl isocyanides in a living/controlled chain growth manner, which led to the formation of poly(phenyl isocyanide)s with controlled molecular weights, narrow molecular weight distributions and high stereoregularity. The Pd unit at the end of the polymer chain could undergo further copolymerization with phenyl isocyanide monomers to give block copolymers. It was also found that the incorporation of an electron-donating group on the phenyl group of the Pd complex could improve the catalytic activities, and the polymerization rate of the phenylethynyl Pd complexes were slightly faster than the phenylbuta-l,3-diynyl Pd complexes. Furthermore, these Pd complexes were tolerant to most organic solvents and applicable to a wide range of isocyanide monomers including alkyl, phenyl isocyanides, even phenyl isocyanide with bulky substituents at the ortho position, and diisocyanide monomers. Bi-and trifunctional Pd complexes with two and three Pd units incorporated into the same phenyl ring were designed and synthesized. They were also able to initiate the living polymerization of phenyl isocyanide to afford telechelic linear and star-shaped polyisocyanides. A phenylethynyl Pd(Ⅱ) complex containing a polymerizable norbornene unit could initiate the living/controlled polymerization of phenyl isocyanide, giving stereoregular poly(phenyl isocyanide)s in high yields. The norbornene unit on the Pd(II) complex can undergo ring-opening metathesis polymerization (ROMP) with Grubbs’second-generation catalyst under a living/controlled manner. Interestingly, the brush copolymer of tunable compositions and high grafting density with polynorbornene as backbone and helical poly(phenyl isocyanide) as side chains can be readily achieved in one-pot via tandem catalysis. The synthesized brush copolymers were revealed to form worm-like cylindrical morphologies and helical rigid-rod architectures in different solvents by atomic force microscope observations.