1,135,248. 1,3 - Diaza - 2 - sila - cycloalkanes. MONSANTO CO. 27 Jan., 1966 [27 Jan., 1965; 5 April, 1965], No. 3797/66. Heading C3S. [Also in Division C5] 1,3-Diaza-2-sila-cycloalkanes of the formula wherein R<SP>1</SP> and R<SP>2</SP> are hydrocarbon, halohydrocarbon or heterocyclic groups having up to 24 carbon atoms, or a group of the formula RY-, where R is a hydrocarbon or fluorocarbon group having up to 24 carbon atoms and Y is oxygen or sulphur, which group may contain additional oxygen or sulphur atoms, or R<SP>1</SP> and R<SP>2</SP> taken together represent a polymethylene chain having up to 7 carbon atoms which chain may be interrupted by one or more oxygen atoms, and R<SP>4</SP> is a hydrocarbylene, substituted hydrocarbylene or divalent heterocyclic group, X is a group having the formula -SiR<SP>1</SP>R<SP>2</SP>R<SP>3</SP> or -R<SP>5</SP>, R<SP>3</SP> is selected from the same groups as R<SP>1</SP> and R<SP>2</SP>, and R<SP>5</SP> is a hydrocarbon or heterocyclic group having up to 24 carbon atoms and X<SP>1</SP> is the same as X or a group having one of the formulae R<SP>6</SP> is a monovalent hydrocarbyl group such that HR<SP>6</SP> is a hydrocarbon which is volatile at the temperature of the reaction and R<SP>7</SP> is a hydrocarbylene group, may be obtained by treating a diamine of the general formula with a catalyst comprising an alkali metal hydride, a complex hydride of an alkali metal or an organo-alkali metal compound having an alkali metal-carbon linkage, which alkali metal has an atomic number of at least 11. The compounds wherein R<SP>1</SP>, R<SP>2</SP>, X and X<SP>1</SP> are methyl groups and R<SP>4</SP> is -CH 2 CH 2 -, and compounds wherein X<SP>1</SP> has either of Formulµ (I) or (II) are not claimed. Specified catalysts are sodium and potassium metals provided there are acidic hydrogens in the system so that their hydrides can be formed in situ, sodium and potassium hydrides, sodium-butyl, potassiumphenyl, sodium naphthyl, NaBH 4 , KBH 4 , NaAlH 4 and KAlH 4 . The cyclization may be effected at temperatures up to 200‹ C., optionally in the presence of a solvent, and a promoter may be added, e.g. a tertiary amine, cobalt or potassium chloride or colloidal metals such as Co, Ni, Cu or Pt. They may also be prepared by reacting a diamine of the formula R<SP>5</SP>NHR<SP>4</SP>-NH 2 or R<SP>5</SP>NH-R<SP>4</SP>-NHR<SP>5</SP> with a triorganohydrosilane of the formula R 1 R 2 R 6 SiH in the presence of at least a catalytic amount of the alkali metal hydride or hydrocarbon, optionally in the presence of an inert solvent and preferably in a molar ratio of at least 1: 3, 1: 2 or 1: 1 and the reaction may be effected stepwise. The groups R 1 , R 2 and R 3 may be alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, aralkyl, aralkenyl, aralkynyl, alkaryl, alkenylaryl, alkynylaryl or heterocyclic groups; they may contain one or more ether linkages or may be substituted by halogen, and they may be linked to silicon through an oxygen or sulphur atom. The divalent group R<SP>4</SP> may be derived from a hydrocarbon containing up to 20 carbons, which may have alkyl, aralkyl or aryl substituents, or from an aromatic ether or thioether, and the amine starting material may be an alkylene, cycloaliphatic, aromatic or heterocyclic diamine; the diamine may be substituted by halogen, oxygen, sulphur, sulphoxide or sulphone groups and it may contain more than two amino groups which may be primary, secondary or tertiary and which may be silylated during the reaction, in some cases yielding bicyclic products. R 6 preferably contains up to 8 carbon atoms and may be selected from methyl, ethyl, vinyl, n-propyl, iso-propyl, allyl, n-, iso-, sec- and tert-butyl and phenyl groups.