Synthesis of High-Purity Dialkylzinc Compounds for Coordinative Chain Transfer Polymerization

R 2 Zn compounds prepared by the conventional method (reaction of 2 eq RMgCl with ZnCl 2 in Et 2 O, followed by filtration to remove MgCl 2 ) are often unsuitable for certain organic and polymer syntheses─particularly coordinative chain transfer polymerization (CCTP)─due to residual impurities. Herein, we disclose a convenient, safe, scalable, and cost-effective method for the preparation of high-purity R 2 Zn that performs effectively in CCTP. In this approach, RMgCl, generated in Et 2 O or the less hazardous (CH 3 O) 2 CH 2, are reacted with ZnCl 2 . Subsequent removal of the ether solvent affords a residue containing both the desired R 2 Zn product and dried MgCl 2 byproduct. The dried MgCl 2 acts as an impurity scrubber during the hexane extraction step, enabling isolation of highly pure R 2 Zn compounds. Using this method, [CH 2 ═C(R)C 6 H 4 (CH 2 ) x ] 2 Zn [ 1 ( x = 3, R = H); 2 ( x = 3, R = Me); 3 ( x = 2, R = H); 4 ( x = 2, R = Me)] was efficiently synthesized. These reagents enabled the formation of high yields of CH 2 ═C(R)C 6 H 4 (CH 2 ) x -[(CH(R)CH 2 )] n -Zn-[(CH 2 CH(R))] n -(CH 2 ) x C 6 H 4 C(R)═CH 2 in CCTP. GPC, 1 H NMR, and rotational rheology analyses of the resulting polymers indicate that a fraction of the styrene units in 1 and 3 is incorporated into the polymer backbone, leading to higher-molecular-weight materials with long-chain branching.