Catalyst and process for preparing color-reduced polyisocyanates containing isocyanurate groups

A process for preparing color-reduced polyisocyanates containing isocyanurate groups, comprising:

• trimerizing at least one diisocyanate in the presence of 0.04-2% by weight, based on weight of said diisocyanate, at least one trimerization catalyst of the formula (I):
• wherein
• and wherein:
• A, B, C, D and E independently of one another or simultaneously are hydrogen, chloro, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkoxycarbonyl, hydroxyl, or phenyl;
• F is hydrogen or methyl;
• R2 and R3 independently of one another or simultaneously are C1-C4 alkyl, C2-C6 hydroxyalkyl with the hydroxyl group in position 2 relative to the quaternary nitrogen or R1;
• R4 is hydrogen, methyl, C2-C10 alkyl, C3-C8 cycloalkyl or C2-C12 alkoxy;
• R5 is C1-C4 alkyl;
• Y− is R6COO− or OH−;
• and
• R6 is hydrogen or a branched or unbranched, aliphatic or araliphatic, C1-C10 alkyl radical.