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Ring-opening of 1,3-dimethyl-1,3-diphenyl- and 1,1,3,3-tetraphenyl-1,3-disilacyclobutane takes place on treatment with halogens, hydrogen halides, lithium aluminium hydride, sodium hydroxide, or sulphuric acid, but the reactions with halogens and hydrogen halides are complicated by silicon-phenyl bond scission. 1,1 -Dimethyl-3,3-diphenyl-1,3-disilacyclobutane is conveniently prepared by reaction of an equimolar mixture of the silanes Me2SiCl·CH2Cl and Ph2SiCl·CH2Cl in tetrahydrofuran with magnesium. It reacts with hydroxide, methoxide, ethoxide, hydride ion, hydrogen chloride, or hydrogen bromide to give major products arising via SiMe2–CH2 bond scission, but in contrast it reacts with chlorine or bromine to give major products arising via SiPh2–CH2 bond scission.

1,1,3,3-Tetramethyl-1,3-disilacyclobutane. (I), reacts with halogens, hydrogen halides, sulphuric acid, lithium tetrahydridoaluminate, phenyl-lithium, phenylmagnesium bromide, ethanolic silver(I) nitrate, ethanolic mercury(II) chloride, and ethanolic mercury(II) acetate to give ring-opened products in high yields; (I) is unaffected by trifluoroiodomethane, N-bromosuccinimide, benzenethiol, heptan-1-ol, basic alumina, sulphur, phenylmercury chloride, or mercury(II) acetate in benzene. Photochemical reaction of t-butyl hypochlorite with (I) gives comparable amounts of 1 -chloromethyl-1,3,3-trimethyl-, 2-chloro-1,1,3,3-tetramethyl-, and 2,2-dichloro-1,1,3,3-tetramethyl-1,3-disilacyclobutane, together with lesser amounts of the ring-opened hydrogen chloride and chlorine 1 : 1 adducts.

1,1,3,3-Tetramethyl-1,3-disilacyclobutane, (I), reacts with iodine monochloride or sodium benzenethiolate in benzenethiol to give reasonable yields of ring-opened 1 :1 adducts, while reaction with bromobis(trifluoromethyl)-amine affords a mixture of perfluoro-2-azapropene and 1-bromo-4-fluoro-2,2.4-trimethyl-2,4-disilapentane via decomposition of the initially formed 1:1 adduct. 1,3-Dimethyl-1,3-diphenyl-1,3-disilacyclobutane, (II), reacts similarly with sodium benzenethiolate in benzenethiol and the bromoamine, but reaction with iodine mono-chloride affords mainly polymeric material. The reaction of sulphur trioxide with compound (II) results in insertion into a ring Si–CH2 bond and a Si–Ph bond in the ratio 9 : 90, while reaction with 1,1,3,3-tetraphenyl-1,3-disila-cyclobutane, (III), gives the Si–Ph insertion product exclusively. Both the phenyl-substituted disilacyclobutanes react with mercury(II) acetate in ethanol to give ring-opened products of the type AcO·Hg·CH2·[graphic omitted]i·CH2·[graphic omitted]i·OEt in high yield.

1,1,3,3-Tetramethyl-1,3-disilacyclobutane, (I), reacts with trichlorosilane or dichloro(methyl)silane in the presence of hexachloroplatinic(IV) acid to give the chlorine-exchange adducts, Me2SiCl·CH2·SiMe2·CH2·SiHCl2(80%) or Me2SiCl·CH2·SiMe2·CH2·SiMeHCl (61%); in the latter reaction the hydrogen-exchange adduct, Me2SiH·CH2·SiMe2·CH2·SiMeCl2(5%). is also formed. A comparable reaction of 1.3-dimethyl-1.3-diphenyl-1,3-disilacyclobutane, (II), with trichlorosilane gives mainly polymeric material together with the chlorine-exchange adduct (10%). Both silacyclobutanes react with tin(IV) chloride in the absence of catalyst or with trimethylsilanol to afford ring-opened 1 :1 adducts in high yield. Compound (I) also reacts with triphenylsilanol to afford hexaphenyldisiloxane and 1,1,3,3-tetramethyl-1,3-bis(trimethylsilylmethyl)disiloxane (87%); (II) does not react under comparable conditions.