Syntheses of 3-Arm and 4-Arm Star-Branched Polystyrene Ru(II) Complexes by the Click-to-Chelate Approach

Zhang, Chunhong; Shen, Xiande; Sakai, Ryosuke; Gottschaldt, Michael; Schubert, Ulrich S.; Hirohara, Shiho; Tanihara, Masao; Yano, Shigenobu; Obata, Makoto; Xiao, Nao; Satoh, Toshifumi; Kakuchi, Toyoji

Abstract:

Metal template synthesis is a useful methodology to make sophisticated macromolecular architectures because of the variety of metal ion coordination. To use metal template methodology, chelating functionalities should be introduced to macromolecules before complexation. In this article, we demonstrate the click-to-chelate approach to install chelating functionality to polystyrene (PS) and complexation with Ru(II) ions to form 3-arm and 4-arm star-branched PS Ru(II) complexes. Azide-terminated PS (PS-N3) was readily prepared by atom transfer radical polymerization using 1-bromoethylbenzene as an initiator followed by substitution of bromine by an azide group. The Cu(I)-catalyzed 1,3-dipolar cycloaddition of PS-N3 with 2-ethynylpyridine or 2,6-diethynylpyridine affords 2-(1H- 1,2,3-triazol-4-yl)pyridine (PS-tapy) or 2,6-bis(1H-1,2,3-triazol-4- yl)pyridine (PS-bitapy) ligands bearing one or two PS chains at the first-position of the triazole rings. Ru(II) complexes of PStapy and PS-bitapy were prepared by conventional procedure. The number-averaged molecular weights (Mns) of these complexes were determined to be 6740 and 10,400, respectively, by size exclusion chromatography using PS standards. These Mn values indicated the formation of 3-arm and 4-arm starbranched PS Ru(II) complexes [Ru(PS-tapy)3](PF6)2 and [Ru(PSbitapy) 2](PF6)2 on the basis of the Mn values of PS-tapy (2090) and PS-bitapy (4970). The structures of these complexes were also confirmed by UV–vis spectroscopy and X-ray crystallography of the Ru(II) complexes [Ru(Bn-tapy)3](PF6)2 and [Ru(Bnbitapy) 2](PF6)2, which bear a benzyl group instead of a PS chain.

Year:

2011

Type of Publication:

Article

Keywords:

atom transfer radical polymerization ATRP; click chemistry; Ru II complex; star-branched polystyrene; star polymer

Journal:

Journal of Polymer Science: Part A: Polymer Chemistry

Volume:

49

Pages:

746 - 754