The invention concerns a novel catalyst for forming urethanes. Said catalyst is characterized by the general formula: MY_3-q[Z]_q, wherein: Z is the radical corresponding to the anion of a super acid whereof the Hamett constant is at least equal to 13 and advantageously more than 13, M representing a trivalent metal, preferably known for forming Lewis acids; Y is an anion or a monovalent anionic function; and q is an integer selected advantageously between 1 and 3, inclusively. The invention is applicable to paint.