A novel titanium (III)-based .beta.-diketonate-coordinated compound is disclosed for catalyzing the polymerization reaction of syndiotactic polystyrenes. The titanium (III)-based compound is represented by the following formula 1: ##STR1## wherein X is a C.sub.1 .about.C.sub.12 alkoxy or amine group, or a halogen atom; R is a C.sub.1 .about.C.sub.12 alkyl, aryl, or alkylsilane group. Preferably, X is N(SiMe.sub.3).sub.2 -- or OMe--, and R is phenyl, methyl, or t-butyl. The titanium (III)-based compounds are prepared by reacting titanium trichloride with diketone and tetrahydrofuran to form an intermediate product, then reacting the intermediate product Ti(AcAc)Cl.sub.2 (THF).sub.2 with either aminosilane or alcohol.