Preparation of organosilanes

A process for preparing a silane of the formula I

• R6R5CH—R4CH—SiR1R2R3 (I),
• which comprises reacting a silane of the formula II
• HSiR1R2R3 (II),
• with an alkene of the formula III
• R6R5CH═CHR4 (III),
• in the presence of an iridium compound of the formula IV as catalyst
• [(diene)IrCl]2 (IV),
• and free diene as cocatalyst, where
• R1, R2, R3 are each independently a monovalent Si—C-bonded, unsubstituted or halogen-substituted C1-C18-hydrocarbon radical, a chlorine atom or a C1-C18-alkoxy radical,
• R4, R5, R6 are each independently a hydrogen atom, a monovalent C1-C18-hydrocarbon radical which is unsubstituted or optionally bears F, Cl, OR, NR′2, CN or NCO substituents, a chlorine atom, a fluorine atom or a C1-C18-alkoxy radical, and where 2 radicals R4, R5, R6 together with the carbon atoms to which they are bound may form a cyclic moiety,
• R is a hydrogen atom or a monovalent C1-C18-hydrocarbon radical and diene is a C4-C50-hydrocarbon compound which is unsubstituted or optionally bears F, Cl, OR, NR′2, CN or NCO as substituents, and has at least two ethylenic C═C double bonds.