Where R44 and R45, R45 and R46, R44 and R46, R44 and R45 and R46, or R49 and R50 form a ring, the ring preferably has 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, most preferably 1 to 6 carbon atoms and may have branched therefrom an alkyl group of 1 to 6 carbon atoms, especially 1 to 4 carbon atoms.