Alternating Copolymerization of Fluoroalkenes with Carbon Monoxide.

The palladium-catalyzed alternating copolymerization of fluoroalkenes, represented as CH2= CH-CH2-Cn-CnF2n+1 with CO was performed using (R,S)-BINAPHOS (2e) as a ligand. The CH2-CnF2n+1 group is the most electronegative substituent ever reported for the copolymerization (Taft's σ* value of 0.90 for CH2CF3). The copolymer obtained from CH2=CH-CH2-C8F17 (1a) existed as a mixture of polyspiroketal and polyketone, while that from CH2=CH-CH2-C4F9 (1b) was a pure polyspiroketal, as was revealed by infrared and 13C-CP/MAS NMR spectroscopies. The terminal structure of the polymer from lb was confirmed by MALDI-TOF MS spectrometry. Detailed NMR studies suggested that the much higher reactivity with (R,S)-BINAPHOS (2e) than that with the conventional ligand DPPP (2a) can be attributed to the unique 1 2-insertion of the fluoroalkene into acylpalladium species. The existence of an electronegative substituent on the a-carbon of the palladium center is successfully avoided in the 1,2- insertion mechanism. [ABSTRACT FROM AUTHOR]