Abstract Sila-3-cyclopentenes were obtained from reaction of 1, 3-butadiene with SiH 2, ClSiH and CH 3 SiH generated from disilane pyrolyses. 1-Silylsila-3-cyclopentene and 1, 2- disila-4-cyclohexene were obtained in near equal quantities from the reaction of 1, 3- butadiene with Si 2 H 4 (H 3 SiSiH or H 2 Si SiH 2) generated from the pyrolysis of Si 3 H 6. Competitive reactions of SiH 2 with 1, 3-butadiene and Si 2 H 6 and of GeH 2 with 1, 3- ...