Reduction Polymerization of CO₂ with Phenylene Silanes Catalyzed by Single Component B(C₆F₅)₃

CO 2 is an abundant C1 resource but a green‐house gas and chemically inert. Thus, its utilization has been a promising but challenging project. Herein, we report the unprecedented polymerization of CO 2 and C 6 H 4 (SiMe 2 H) 2 using B(C 6 F 5 ) 3 alone under mild conditions to give poly(silphenylene siloxane) accompanied by releasing CH 4 . The copolymerization can be extended to comonomers of phenylene silanes bearing functional groups. Moreover, it combines with Piers‐Rubinsztajn reaction to establish a tandem polymerization system to achieve super thermal resistant poly(siloxane‐co‐silphenylene siloxane)s. Density functional theory reveals that B(C 6 F 5 ) 3 is activated by silanes to form free HB(C 6 F 5 ) 2 , which is the true active species for CO 2 reducing to borylformate, the rate controlling step of the polymerization procedure. The subsequent multiple reductions of borylformate to CH 4 and the step‐growth to poly(silphenylene siloxane)s can be fulfilled by both B(C 6 F 5 ) 3 and HB(C 6 F 5 ) 2 , and the former shows a slightly higher activity. This work opens a new avenue of utilizing CO 2 to fabricate polysiloxanes that is unable to access using current manners.