Synthesis of Stereoregular and Optically Active Poly[{methyl(1-naphthyl)silylene}(o-phenylene)methylene] by Platinum-Catalyzed Ring-Opening Polymerization

Reaction of 1-methyl-1-(1-naphthyl)-2,3-benzosilacyclobut-2-ene ( 1 ) with platinum 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (PDT) as catalyst (0.1 mol %) gave a polymer, possibly cyclic, with M n = 1 210 000, polydispersity index (PDI) = 1.77, and cyclic dimer produced via a reductive-elimination. Reaction of 1 with PDT in the presence of Et 3 SiH (1:Et 3 SiH = 1:1) gave 1-triethylsilyl-2-{methyl(1-naphthyl)silylmethyl}benzene ( 2 ), a dimer, 1-{methyl(1-naphthyl)(2‘-triethylsilylphenylmethyl)silyl}-2-{methyl(1-naphthyl)silylmethyl}benzene ( 3 ), and a trimer, 1-{methyl(1-naphthyl)(2‘-triethylsilylphenylmethyl)silyl}-2-[methyl(1-naphthyl)[2‘-{methyl(1-naphthyl)silylmethylphenyl}]silylmethyl]benzene, in 54, 18, and 11% yield, respectively, through a regioselective ring-opening reaction, followed by the σ-bond metathesis process. The molecular weight of the formed polymers can be controlled by the amount of Et 3 SiH. When optically pure ( + )-1 was used, 2 and 3 are proved to have enantiomer excess (ee) or optical purity (op) higher than 99%. These products are considered to be formed from the intermediate cyclic Pt complexes, which were formed by a regio- and stereoselective oxidative-addition of silicon-aryl bond of ( + )-1 to Pt, followed by a stereoselective σ-bond metathesis process. Pt-catalyzed ring-opening polymerization (ROP) of optically pure ( + )-1 provided an isotactic and optically pure polymer [ M n = 356 000, PDI = 1.73, [α] 27 D = −33.5, c 1.11, CHCl 3 ].