Pd-Catalyzed Cross-Coupling Using Polymer-Supported Siloxane

Key words

siloxane - organolithium compounds - cross-coupling

Significance

Polymer-supported siloxane-transfer agent PSTA-I₂₀₀ was prepared by the ring-opening metathesis polymerization of siloxane 1, which was synthesized from commercially available 5-norbornene-2-carboxaldehyde (eq.1). ­Palladium-catalyzed cross-coupling reactions of aryl- and alkenyllithium with organohalides were achieved by using stoichiometric amounts of PSTA-I₂₀₀ (eq. 2, 9 examples, up to 98% yield).

Comment

PSTA-I₂₀₀ was characterized with IR, NMR, and GPC. After the cross-coupling reaction, PSTA-I₂₀₀ was recovered via precipitation with MeCN. In the reaction of phenyllithium with 4-iodoanisole, PSTA-I₂₀₀ was reused twice with a small decrease of reaction efficiency (1^st reuse; 91% yield, 2^nd reuse; 81% yield). An increase in the average molecular weight of the recovered PSTA-I₂₀₀ was observed, probably due to polymer cross-linking by the attack of the oxyanion generated in situ on another siloxane of a different polymer chain.