Patent ID: 7091151

Claim:
A catalytic system consisting of a metal complex of formula M(OR 8 ) 4-n X n (VII) wherein M is a tetravalent metal cation selected from the group 4 of the periodic table, R 8 represents a C 1-6 linear or branched alkyl group, X represents an halide such as a Cl or F atom and the index n represents an integer from 1 to 3; and of a co-ingredient which is an alkyl or aromatic carboxylic acid anhydride containing 1 to 10 carbon atoms, BF 3 or an anhydrous salt selected from the group consisting of the sulfates, chlorides and bromides of a metal cation, said metal cation being selected from the group consisting of Li + , Na + , K + , Cs + , Mg 2+ , Ni 2+ , Ca 2+ , Zn 2+ , Fe 3+ and Al 3+ .