The invention relates to an initiator comprising at least one structural element characterized by the following formula (I) wherein X.sup.- is a non or low coordinating anion, R1, R2, R3, R4 are independently linear, cyclic or branched C.sub.1-C.sub.20 alkyl or alkylene groups, wherein one or more of the methylene groups contained in the alkyl or alkylene group can be substituted by --CO--, --CONH--, --CON(CH.sub.3)--, --S-- and/or --O--, and wherein R1, R2, R3 and/or R4 can act as a bridging element connecting two or more structural elements. The invention is also related to a process of producing the initiator and to a curable composition comprising the initiator, a process for producing the curable composition a kit comprising a cationically curable composition and the inventive initiator and the use of the initiator or the curable composition comprising the initiator for various applications, especially in the dental field.