Synthesis of 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 11-, and 12-armed star-shaped poly(styrene oxide) Ru(ii) complexes by a click-to-chelate approach

Abstract

This study describes the first convenient preparation of 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 11-, and 12-armed star-shaped poly(styrene oxide) (PSO) Ru(II) complexes using a click-to-chelate approach. This approach involves the combination of the click reaction and stepwise chelating reactions of Ru(II)(DMSO)₄Cl₂ with macroligands, 2-(1-PSO_n-1,2,3-triazol-4-yl)pyridine (PSO_n-tapy) or 2-(1-PSO_m-1,2,3-triazol-4-yl)-6-(1-PSO_n-1,2,3-triazol-4-yl)pyridine (PSO_m-bitapy-PSO_n) (m, n = 1, 2, or 3). Click chemistry was used to prepare the PSO_n-tapy and PSO_m-bitapy-PSO_n macroligands. More specifically, PSO_n-tapy was prepared by reacting the azido-functionalized PSO_n (PSO_n-N₃) with excess 2-ethynylpridine. On the other hand, PSO_m-bitapy-PSO_n was obtained by the click reaction of excess PSO_n-N₃ with 2,6-diethynylpridine to afford (PSO_n)₂-bitapy when m equals n, and by the stepwise click reactions of PSO_m-N₃ and PSO_n-N₃ with 2,6-diethynylpridine to produce PSO_m-bitapy-PSO_n when m is not equal to n. In order to obtain these polymer-substituted macroligands, PSO_n-N₃ was initially synthesized by the living ring-opening polymerization (ROP) of styrene oxide (SO) using t-Bu-P₄ as a catalyst and the azido-functionalized mono- or multi-hydroxyl compounds, e.g., 6-azido-1-hexanol, 2-((6-azidohexyloxy)methyl)-2-methylpropane-1,3-diol (1) and 2-((6-azidohexyloxy)methyl)-2-(hydroxymethyl)propane-1,3-diol (2) as initiators.