A method for preparing hydrosilylation and/or dehydrogenative silylation products by reaction between: - an unsaturated compound A selected from the organopolysiloxane compounds comprising units of formula: Z g U h SiO (4-(g+h))/2 wherein: - the radicals Z, identical or different, represent an alkenyl or alkynyl radical, linear or branched, having 2 to 6 carbon atoms; - the radicals U, identical or different, represent a hydrocarbon radical having 1 to 12 carbon atoms; - g = 1 or 2, h = 0, 1 or 2 and g+h =1, 2 or 3; and possibly comprising other units of formula: U i SiO (4-i)/2 wherein U has the same meaning as above and i = 0, 1, 2 or 3; - and a compound B comprising at least one silyl hydride function, - where said method is characterized by the fact that the hydrosilylation and/or dehydrogenative silylation reaction is catalyzed by an iron compound C of formula: [Fe(N(SiR 3) 2) x] y wherein: - the symbols R, identical or different, represent a hydrogen atom or a hydrocarbon radical having 1 to 12 carbon atoms, and preferably the symbols R, identical or different, are selected from the group consisting of: hydrogen atom, alkyl groups having 1 to 8 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms; - x=1, 2 or 3; and - y=1 or 2. - an unsaturated compound A selected from the organopolysiloxane compounds comprising units of formula: Z g U h SiO (4-(g+h))/2 wherein: - the radicals Z, identical or different, represent an alkenyl or alkynyl radical, linear or branched, having 2 to 6 carbon atoms; - the radicals U, identical or different, represent a hydrocarbon radical having 1 to 12 carbon atoms; - g = 1 or 2, h = 0, 1 or 2 and g+h =1, 2 or 3; and possibly comprising other units of formula: U i SiO (4-i)/2 wherein U has the same meaning as above and i = 0, 1, 2 or 3; - and a compound B comprising at least one silyl hydride function, - where said method is characterized by the fact that the hydrosilylation and/or dehydrogenative silylation reaction is catalyzed by an iron compound C of formula: [Fe(N(SiR 3) 2) x] y wherein: - the symbols R, identical or different, represent a hydrogen atom or a hydrocarbon radical having 1 to 12 carbon atoms, and preferably the symbols R, identical or different, are selected from the group consisting of: hydrogen atom, alkyl groups having 1 to 8 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms; - x=1, 2 or 3; and - y=1 or 2. - the radicals Z, identical or different, represent an alkenyl or alkynyl radical, linear or branched, having 2 to 6 carbon atoms; - the radicals U, identical or different, represent a hydrocarbon radical having 1 to 12 carbon atoms; - g = 1 or 2, h = 0, 1 or 2 and g+h =1, 2 or 3; - and a compound B comprising at least one silyl hydride function, - where said method is characterized by the fact that the hydrosilylation and/or dehydrogenative silylation reaction is catalyzed by an iron compound C of formula: [Fe(N(SiR 3) 2) x] y wherein: - the symbols R, identical or different, represent a hydrogen atom or a hydrocarbon radical having 1 to 12 carbon atoms, and preferably the symbols R, identical or different, are selected from the group consisting of: hydrogen atom, alkyl groups having 1 to 8 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms; - x=1, 2 or 3; and - y=1 or 2. - the symbols R, identical or different, represent a hydrogen atom or a hydrocarbon radical having 1 to 12 carbon atoms, and preferably the symbols R, identical or different, are selected from the group consisting of: hydrogen atom, alkyl groups having 1 to 8 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms; - x=1, 2 or 3; and - y=1 or 2.