Silicone composition which can be crosslinked into an elastomer by hydrosilylation in the presence of carbene-based metal catalysts, and catalysts of this type

1. A silicone composition which is crosslinkable by hydrosilylation, said composition comprising at least one PolyOrganoSiloxane -A- (POS) carrying ethylenic and/or acetylenic unsaturation(s), at least one polyorganohydrosiloxane —B—, a metal catalyst —C— and optionally at least one inhibitor -D- of the hydrosilylation reaction; said catalyst —C— comprising at least one compound having the formula (I):

in which:

M represents a metal of Group 8 of the Periodic Table;

L γ represents a carbene of formula (II):

in which:

A and B, which are identical or different, represent C or N, it being understood that, when A represents N, then T 4 does not represent anything and, when B represents N, then T 3 does not represent anything;

T 3 and T 4 independently represent a hydrogen atom; an alkyl group; a cycloalkyl group optionally substituted by alkyl or alkoxy; an aryl group optionally substituted by alkyl or alkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group in which the aryl part is optionally substituted by alkyl or alkoxy; or

T 3 and T 4 can together and with A and B, when the latter each represent a carbon atom, form an aryl;

T 1 and T 2 independently represent an alkyl group; an alkyl group optionally substituted by alkyl; a perfluorinated alkyl group or an alkyl group optionally substituted by a perfluoroalkyl group; a cycloalkyl group optionally substituted by alkyl or alkoxy; an aryl group optionally substituted by alkyl or alkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group in which the aryl part is optionally substituted by alkyl or alkoxy; or

T 1 and T 2 independently represent a monovalent radical of following formula (V):

V 1 —V 2   (V)

 in which:

V 1 is a divalent hydrocarbonaceous radical,

V 2 is a monovalent radical selected from the group consisting of the following substituents:

alkoxy, —OR o wherein R o is hydrogen, alkyl or aryl, and amine;

T 1 and T 2 independently represent a monovalent radical of following formula (W):

W 1 —ω—W 2   (W)

 in which:

W 1 is a divalent hydrocarbonaceous radical;

ω represents:

—R 1 C═CR 1 — wherein R 1 is H or alkyl,

or

—C≡C—;

W 2 is a monovalent radical selected from the group consisting of the following substituents:

R 2 , which is alkyl or H;

Si-alkyl or Si-alkoxy;

alcohol;

ketone;

carboxyl;

amide; and

acyl; or

the substituents T 1 , T 2 , T 3 and T 4 form in pairs, when they are situated at two adjacent points in the formula (II), a saturated or unsaturated hydrocarbonaceous chain;

and with the condition that at least one substituent T 1 and/or T 2 , which are identical or different, represent(s) a monovalent radical of following formula (V):

Z 1 -Z 2   (V)

in which:

Z 1 is a divalent hydrocarbonaceous radical, and

Z 2 is a monovalent radical selected from the group consisting of:

a (C 5 —C 30 )cycloalkyl radical having at least one heteroatom in the ring, and

a (C 6 —C 30 )aryl radical having at least one heteroatom in the aromatic ring,

L α and L β are ligands which are identical to or different from each other and each represent:

Z 1 —≡—Z 2   (III.1)

 wherein, in these formulae (III.1) and (III.2):

z 1 , z 2 , Z 3 , Z 4 , Z 5 and Z 6 each independently represent:

hydrogen,

halogen,

cyano, or

a saturated or unsaturated, electron-withdrawing or non-electron-withdrawing, hydrocarbonaceous group,

or two vicinal Z 1 to Z 6 groups together form an electron-withdrawing or non-electron-withdrawing ring which optionally comprises heteroatoms;

or L α and L β together form the ligand L δ of formula (IV):

 in which:

Y 1 and Y 2 represent, independently of each other, CR a R b or SiR C R d ;

X represents O, NR e or CR f R g ;

R 10 , R 11 , R 13 and R 14 , which are identical or different, are selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group optionally substituted by alkyl;

R 9 , R 12 , R a , R b and R e are selected independently from the group consisting of a hydrogen atom; an alkyl group; an acyl group; an aryl group optionally substituted by alkyl; a cycloalkyl group optionally substituted by alkyl; and an arylalkyl group in which the aryl part is optionally substituted by alkyl;

R c and R d are selected independently from the group consisting of alkyl; aryl optionally substituted by alkyl; cycloalkyl optionally substituted by alkyl; and arylalkyl in which the aryl part is optionally substituted by alkyl; or

when Y 1 and Y 2 independently represent SiR c R d , two R c groups bonded to two separate silicon atoms together form a chain of the formula:

 in which n is an integer from 1 to 3; X is as defined above; R and R′, which are identical or different, have any one of the meanings given above for R e , it being understood that, when n is 2 or 3, only one silicon atom of the said chain may be substituted by one or two alkenyl or alkynyl groups; or

when Y 1 and Y 2 independently represent SiR c R d , two R c groups bonded to separate silicon atoms together form a saturated hydrocarbonaceous chain, the two R c groups forming, together with the said silicon atoms and X, a 6- to 10-membered ring; or

when Y 1 and Y 2 independently represent CR a R b , two R a groups bonded to separate carbon atoms together form a saturated hydrocarbonaceous chain, the two R a groups forming, together with the carbon atoms which carry them and X, a 6- to 10-membered ring; and

R f and R g represent, independently of each other, a hydrogen atom; an alkyl group; an acyl group; an aryl group optionally substituted by alkyl;

a cycloalkyl group optionally substituted by alkyl; an arylalkyl group in which the aryl part is optionally substituted by alkyl; a halogen atom; an alkenyl group; an alkynyl group; or an SiG 1 G 2 G 3 group where G 1 , G 2 and G 3 are, independently of one another, alkyl; alkoxy; aryl optionally substituted by alkyl or alkoxy; or arylalkyl in which the aryl part is optionally substituted by alkyl or alkoxy.

2. A composition according to claim 1 , wherein M is Pt, Pd or Ni in the zero oxidation state.

3. A composition according to claim 1 , wherein in the formula (II):

T 3 and T 4 represent a hydrogen atom or together form phenyl, and/or

only one of T 1 or and T 2 represents (C 1 —C 8 )alkyl or (C 3 —C 8 )cycloalkyl, and/or

A and B both represent a carbon atom.

4. A composition according to claim 1 , wherein in formulae (III.1) and (III.2), the electron-withdrawing groups are selected from the group consisting of:

in which:

R 17 , R 18 , R 19 and R 20 are each a substituted or unsubstituted alkyl, alkenyl or alkynyl and n′ is between 1 and 50.

5. A composition according to claim 1 , wherein:

Z 1 , Z 2 , Z 3 , Z 4 , Z 5 and Z 6 are selected from the group consisting of —COOCH 3 , —COOCH 2 CH 3 , —CONC 12 H 25 and —CN;

or, wherein, when the Z 1 and Z 2 substituents form in pairs and with the triple bond, in (III.1), a ring Cy1 or wherein when Z 3 to Z 6 form in pairs, with or without the double bond, in (III.2), a ring Cy2, said rings Cy1 and Cy2 are independently selected from the group consisting of:

6. A composition according to claim 1 , wherein L α and L β together form a ligand L δ of formula (IV) in which Y 1 and Y 2 either both represent CR a R b or both represent SiR c R d , so that the complexes have the formula (IV.1) or the formula (IV.2):

wherein the two R a groups, the two R b groups, the two R c groups and the two R d groups are identical to one another and R 9 ═R 12 ; R 10 ═R 14 ; and R 11 ═R 13 .

7. A composition according claim 1 , wherein the catalyst —C— has the formula (I.1):

in which:

T 1 and T 2 are identical and are as defined in claim 13 ;

T 3 and T 4 are as defined in claim 1 ; and

and R c and R d are as defined in claim 13 .

8. A composition according to claim 1 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0,1, 2, or 3;

y is an integer equal to 0,1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

9. The composition according to claim 1 , wherein V 1 is alkylene and, when V 2 is an amine, it has the formula N(R o ) 2 wherein R o is hydrogen, alkyl or aryl.

10. The composition according to claim 1 , wherein W 1 is linear or branched C 1 —C 10 alkylene, which is optionally substituted.

11. The composition according to claim 1 , wherein W 2 is alkyl, H, —Si(R 3 ) 3 wherein R 3 is alkyl, C(R 4 ) 2 OH wherein R 4 is H or alkyl, —C(O)R 5 wherein R 5 is alkyl, —C(O)OR 6 wherein R 6 is alkyl, —C(O)N(R 7 ) 2 wherein R 7 is H or alkyl, or —OC(O)R 8 wherein R 8 is alkyl.

12. The composition according to claim 1 , wherein in formula (V), Z 1 is alkylene and Z 2 is (C 5 — 30 )cycloalkyl having at least one nitrogen atom in the ring or (C 6 —C 30 )aryl having at least one nitrogen atom in the aromatic ring.

13. The composition according to claim 1 , wherein in formula (III.1) and (III.2), when Z 1 , Z 2 , Z 3 , Z 4 , Z 5 and/or Z 6 is an unsaturated electron-withdrawing or non-electron-withdrawing, hydrocarbonaceous group, it is unsaturated adjacent to the double or triple bond.

14. The composition according to claim 1 , wherein in formulae (III.1) and (III.2), when two vicinal Z 1 to Z 6 groups together form an electron-withdrawing or non-electron-withdrawing ring, said ring is other than the carbene L γ of formula (II) and optionally has heteroatoms selected from the group consisting of O, N and S.

15. The composition according to claim 2 , wherein M is platinum in the zero oxidation state.

16. The composition according to claim 3 , wherein only one of T 1 and T 2 represents methyl, n-propyl, n-pentyl, cyclohexyl, adamantyl, allyl, methallyl, propargyl or homopropargyl.

17. The composition according to claim 6 , wherein X in formula (IV.1) and (IV.2) is an oxygen atom.

18. The composition according to claim 1 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0,1, 2, or 3;

y is an integer equal to 0,1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

19. The composition according to claim 2 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

20. The composition according to claim 3 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

21. The composition according to claim 4 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

22. The composition according to claim 5 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

23. The composition according to claim 6 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4-y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

24. The composition according to claim 7 , wherein the POSs -A- and —B— are chosen from those composed of siloxyl units of the formula:

(R 20 ) x SiO (4-x)/2   (I′)

and/or of siloxyl units of the formula:

(R 21 ) y (R 22 ) z SiO (4y-z)/2   (II′)

in which formulae the symbols have the following meanings:

R 20 and R 22 , which are identical or different, each represent a group with a nonhydrolyzable hydrocarbonaceous nature which is:

an alkyl or haloalkyl radical having from 1 to 5 carbon atoms and having from 1 to 6 chlorine and/or fluorine atoms,

a cycloalkyl or halocycloalkyl radical having from 3 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms,

an aryl, alkylaryl or haloaryl radical having from 6 to 8 carbon atoms and having from 1 to 4 chlorine and/or fluorine atoms, or

a cyanoalkyl radical having from 3 to 4 carbon atoms;

R 21 represents a hydrogen atom, a C 2 —C 6 alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group, provided that when there are multiple R 21 groups, they are identical or different;

x is an integer equal to 0, 1, 2, or 3;

y is an integer equal to 0, 1, 2, or 3;

z is an integer equal to 0, 1 or 2;

and the sum y+z is from 1 to 3 inclusive;

with the condition that the Si-alkenyl POS -A- comprises at least one unit R 21 ═alkenyl per molecule and the Si—H POS —B— comprises at least one unit R 21 ═hydrogen per molecule.

25. A metal complex or catalyst comprising at least one compound having the formula (I):

in which:

M represents a metal of Group 8 of the Periodic Table;

L γ represents a carbene of formula (II):

in which:

A and B, which are identical or different, represent C or N, it being understood that, when A represents N, then T 4 does not represent anything and, when B represents N, then T 3 does not represent anything;

T 3 and T 4 independently represent a hydrogen atom; an alkyl group; a cycloalkyl group optionally substituted by alkyl or alkoxy; an aryl group optionally substituted by alkyl or alkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group in which the aryl part is optionally substituted by alkyl or alkoxy; or

T 3 and T 4 can together and with A and B, when the latter each represent a carbon atom, form an aryl;

T 1 and T 2 independently represent an alkyl group; an alkyl group optionally substituted by alkyl; a perfluorinated alkyl group or an alkyl group optionally substituted by a perfluoroalkyl group; a cycloalkyl group optionally substituted by alkyl or alkoxy; an aryl group optionally substituted by alkyl or alkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group in which the aryl part is optionally substituted by alkyl or alkoxy; or

T 1 and T 2 independently represent a monovalent radical of following formula (V):

V 1 —V 2   (V)

 in which:

V 1 is a divalent hydrocarbonaceous radical,

V 2 is a monovalent radical selected from the group consisting of the following substituents:

alkoxy, —OR o wherein R o is hydrogen, alkyl or aryl, and amine;

T 1 and T 2 independently represent a monovalent radical of following formula (W):

W 1 —ω—W 2   (W)

 in which:

W 1 is a divalent hydrocarbonaceous radical;

ω represents:

—R 1 C═CR 1 — wherein R 1 is H or alkyl,

or

—C≡C—;

W 2 is a monovalent radical selected from the group consisting of the following substituents:

R 2 , which is alkyl or H;

Si-alkyl or Si-alkoxy;

alcohol;

ketone;

carboxyl;

amide; and

acyl; or

the substituents T 1 , T 2 , T 3 and T 4 form in pairs, when they are situated at two adjacent points in the formula (II), a saturated or unsaturated hydrocarbonaceous chain;

and with the condition that at least one substituent T 1 and/or T 2 , which are identical or different, represent(s) a monovalent radical of following formula (V):

Z 1 -Z 2   (V)

in which:

Z 1 is a divalent hydrocarbonaceous radical, and

Z 2 is a monovalent radical selected from the group consisting of:

a (C 5 —C 30 )cycloalkyl radical having at least one heteroatom in the ring, and

a (C 6 —C 30 )aryl radical having at least one heteroatom in the aromatic ring,

L α and L β are ligands which are identical to or different from each other and each represent:

 wherein, in these formulae (III.1) and (III.2):

Z 1 , Z 2 , Z 3 , Z 4 , Z 5 and Z 6 each independently represent:

hydrogen,

halogen,

cyano, or

a saturated or unsaturated, electron-withdrawing or non-electron-withdrawing, hydrocarbonaceous group,

or two vicinal Z 1 to Z 6 groups together form an electron-withdrawing or non-electron-withdrawing ring which optionally comprises heteroatoms;

or L α and L β together form the ligand L δ of formula (IV):

 in which:

Y 1 and Y 2 represent, independently of each other, CR a R b or SiR c R d ;

X represents O, NR e or CR f R g ;

R 10 , R 11 , R 13 and R 14 , which are identical or different, are selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group optionally substituted by alkyl;

R 9 , R 12 , R a , R b and R e are selected independently from the group consisting of a hydrogen atom; an alkyl group; an acyl group; an aryl group optionally substituted by alkyl; a cycloalkyl group optionally substituted by alkyl; and an arylalkyl group in which the aryl part is optionally substituted by alkyl;

R c and R d are selected independently from the group consisting of alkyl; aryl optionally substituted by alkyl; cycloalkyl optionally substituted by alkyl; and arylalkyl in which the aryl part is optionally substituted by alkyl; or

when Y 1 and Y 2 independently represent SiR c R d , two R c groups bonded to two separate silicon atoms together form a chain of the formula:

 in which n is an integer from 1 to 3; X is as defined above; R and R′, which are identical or different, have any one of the meanings given above for R e , it being understood that, when n is 2 or 3, only one silicon atom of the said chain may be substituted by one or two alkenyl or alkynyl groups; or

when Y 1 and Y 2 independently represent SiR c R d , two R c groups bonded to separate silicon atoms together form a saturated hydrocarbonaceous chain, the two R c groups forming, together with the said silicon atoms and X, a 6- to 10-membered ring; or

when Y 1 and Y 2 independently represent CR a R b , two R a groups bonded to separate carbon atoms together form a saturated hydrocarbonaceous chain, the two R a groups forming, together with the carbon atoms which carry them and X, a 6- to 1 0-membered ring; and

R f and R g represent, independently of each other, a hydrogen atom; an alkyl group; an acyl group; an aryl group optionally substituted by alkyl;

a cycloalkyl group optionally substituted by alkyl; an arylalkyl group in which the aryl part is optionally substituted by alkyl; a halogen atom; an alkenyl group; an alkynyl group; or an SiG 1 G 2 G 3 group where G 1 , G 2 and G 3 are, independently of one another, alkyl; alkoxy; aryl optionally substituted by alkyl or alkoxy; or arylalkyl in which the aryl part is optionally substituted by alkyl or alkoxy.

26. A metal complex or catalyst according to claim 25 , wherein M is Pt, Pd or Ni in the zero oxidation state.

27. A metal complex according to claim 25 , wherein L α and L β together form a ligand L δ of formula (IV) in which Y 1 and Y 2 either both represent CR a R b or both represent SiR c R d , so that the complexes have the formula (IV.1) or the formula (IV.2):

wherein the two R a groups, the two R b groups, the two R c groups and the two R d groups are identical to one another and R 9 ═R 12 ; R 10 ═R 14 ; and R 11 ═R 13 .

28. A metal complex or catalyst according to claim 25 , having the formula (I.1):

in which:

T 1 and T 2 are identical and are as defined in claim 25 ;

T 3 and T 4 are as defined in claim 25 ; and

and R c and R d are as defined in claim 25 .

29. A process for the hydrosilylation of olefins or of acetylenic derivatives, said process comprising heating a composition according to claim 1 at about 100° C. or greater to crosslink its -A- and —B— polyorganosiloxane components.

30. A process for the hydrosilylation of olefins or of acetylenic derivatives, said process comprising heating at least one PolyOrganoSiloxane -A- (POS) carrying ethylenic and/or acetylenic unsaturations and at least one polyorganohydrosiloxane —B—, in the presence of a metal complex or catalyst as defined in to claim 25 at about 100° C. or greater to crosslink said -A- and —B— components.

31. The process according to claim 29 , wherein the catalyst C in the composition comprises at least one ligand L α or L β of formula (III.1) or (III.2).

32. The process according to claim 29 , wherein the composition comprises at least one inhibitor -D- which is a ligand L α or L β of formula (III.1) or (III.2).