Alternating copolymerization of arylallenes with carbon monoxide catalyzed by a π-allylrhodium complex.: Synthesis of new polyketones with regulated structure and molecular weight

A pi-allylrhodium complex, Rh[eta(3)-CH(Ar)C{C(=CHAr)CH2C(=CHAr)CH2CH2CH=CHAr}- CH2](PPh3)(2) (Ar = C6H4OMe-p) (1), catalyzes alternating copolymerization of arylallenes (phenylallene, (4-methylphenyl)allene, (4-methoxyphenyl)allene, (4-chlorophenyl)allene, (4-fluorophenyl)allene, (4-butylphenyl)allene, and (4-tert-butylphenyl)allene) with carbon monoxide (1 atm) at room temperature to give the corresponding polyketones, I-[-CO-C(=CHAr)CH2-](n) (I = CH2C(=CHAr)C(=CHAr)CH2C(=CHAr)CH2CH2CH=CHAr, where Ar = C6H4OMe-p). The polymers contain the 2,3-polymerized arylallene unit rather than the 1,2-polymerized unit. The C=C double bond in the repeating unit has a Z configuration, which is confirmed by the H-1 NMR spectrum using ROESY technique. The living polymerization is demonstrated by (1) the H-1 NMR spectrum of the polymers showing signals of the terminal group I originally contained in 1, (2) an increase in molecular weight (M-n) of the polymer with narrow polydispersity throughout the polymerization, and (3) a linear relationship between the molecular weight and the monomer-to-catalyst ratio. Copolymerization of phenylallene with carbon monoxide catalyzed by 1 and subsequent addition of (4-methoxyphenyl)allene to the reaction mixture afford the block copolyketone I-[{-CO-C(=CHPh)-CH2-}(m)-{CO-C(=CH-C6H4OMe-p)-CH2-}(n)], while copolymerization of an equimolar mixture of phenylallene and (4-methoxyphenyl)allene with carbon monoxide gives the random copolyketone I-{-CO-C(=CHPh)-CH2-/-CO-C(=CHC6H4OMe-p)-CH2-}(n). These two copolyketones are characterized by comparison of the C-13{H-1} NMR spectra.