Grignard reagents featuring carbanion characteristics are generally unreactive toward alkyl halides and require a catalyst for the coupling reaction. With the need to synthesize p-(CH2=CH)C6H4CH2CH2CH2Cl on a large-scale, the coupling reaction of p-(CH2=CH)C6H4MgCl with BrCH2CH2CH2Cl was attempted to screen the catalysts, and CuCN was finally determined to be the best catalyst affording the desired compound in 80% yield with no generation of Wurtz coupling side product CH2=CHC6H4C6H4CH=CH2. The p-(CH2=CH)C6H4Cu(CN)MgCl species was proposed as an intermediate based on the X-ray structure of PhCu(CN)Mg(THF)4Cl. The structures of p-(CH2=CH)C6H4CH2CH2CH2MgCl and p-ClC6H4MgCl were also elucidated, which existed as an aggregate with MgCl2, proposing that some portion of the Grignard reagents were possibly lost in the coupling reaction owing to co-precipitation with the byproduct MgCl2. Using the developed syntheses, [p-(CH2=CH)C6H4CH2CH2CH2]2Zn which is latently useful compound for the production of PS-block-PO-block-PS, respectively, was successfully synthesized with considerable cost reductions.
