Hindered piperidine ligands

A compound of the formula H.sub.r L wherein r is 1 or 2, and L is a group of formula II ##STR44## in which R.sub.1 is hydrogen or C.sub.1 -C.sub.4 alkyl, Z.sub.1 is hydrogen or a group of formula III ##STR45## R.sub.6 is a group of formula V ##STR46## in which R.sub.9 is hydrogen or C.sub.1 -C.sub.4 alkyl, and R.sub.7 and R.sub.8 independently of each other are hydrogen, methyl, phenyl, C.sub.2 -C.sub.9 alkoxymethyl or a --CH.sub.2 --O--R.sub.6 radical, in which R.sub.6 is as defined above, and a is 0, 1 or 2 and b is 0 or 1 and c is 0 or, if a and/or b differ from 0, is also 1, and X and Y independently of each other are --O-- or ##STR47## in which R.sub.10 is hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.3 -C.sub.8 alkenyl, cyclohexyl, C.sub.3 -C.sub.21 alkoxyalkyl, C.sub.7 -C.sub.13 aralkyl, phenyl, or phenyl substituted by C.sub.1 -C.sub.8 alkyl and/or by C.sub.1 -C.sub.8 alkoxy, or a group --CH.sub.2 --CH.sub.2 --O--R.sub.6' in which R.sub.6 is as defined above, and R.sub.10 is also a group of the formula VI ##STR48## in which R.sub.1 is as defined above and R.sub.11 is hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.3 -C.sub.8 alkenyl, C.sub.2 -C.sub.21 alkoxyalkyl, C.sub.7 -C.sub.8 aralkyl, an alkanoyl or alkenoyl having 1-4 C atoms, or a group --CH.sub.2 COOR.sub.2'

• R.sub.2 is C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.6 alkenyl, phenyl, C.sub.7 -C.sub.8 aralkyl or cyclohexyl, and Z.sub.2 is hydrogen, C.sub.2 -C.sub.18 alkanoyloxy, benzoyloxy, or benzoyloxy substituted by C.sub.1 -C.sub.8 alkyl or by C.sub.1 -C.sub.8 alkoxy, or C.sub.2 -C.sub.18 alkanoylamido or said alkanoylamido substituted on the N-atom by C.sub.1 -C.sub.8 alkyl, or one of the groups --R.sub.12, --(CH.sub.2).sub.d --R.sub.12, ##STR49## in which is 2 to 10 and R.sub.12 is a group of the formula VII ##STR50## in which R.sub.1 and Z.sub.1 are as defined above, or Z.sub.2 is also a group of the formula VIII ##STR51## in which R.sub.12 is as defined above and X' is --O-- or ##STR52## in which R.sub.14 is hydrogen or C.sub.1 -C.sub.4 alkyl, and R.sub.13 is --(CH.sub.2).sub.e -- or a group ##STR53## in which e is 0, or 2 to 8 and R.sub.15 and R.sub.16 independently of one another are hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.3 -C.sub.8 alkenyl, C.sub.7 -C.sub.11 aralkyl, cyanomethyl, cyanoethyl or a group --CH.sub.2 COOR.sub.17, in which R.sub.17 is methyl or ethyl, or Z.sub.2 is one of the groups ##STR54## in which R.sub.6, R.sub.7 and R.sub.12 are as defined above and R.sub.18 is hydrogen, C.sub.1 -C.sub.8 alkyl, allyl, phenyl or benzyl and R.sub.19 is hydrogen, C.sub.1 -C.sub.8 alkyl, allyl or benzyl and R.sub.20 is C.sub.1 -C.sub.4 alkyl or a group of the formula V which is as defined above, and R.sub.21 is C.sub.2 -C.sub.6 alkylene, cyclohexylidene, phenylene, diphenylene, 4,4'-diphenylene oxide or 4,4'-diphenylenemethane, or Z.sub.2 is also a group of the formulae XII, XIII or XIV ##STR55## in which a, b, c, X, Y, R.sub.6, R.sub.7 and R.sub.8 are as defined above and f, a' and b' are 0 or 1 and g is 0 or, if a' and/or b' differ from 0, is also 1, and R.sub.22 and R.sub.23 independently of one another are hydrogen, C.sub.1 -C.sub.4 alkyl, cyclohexyl, phenyl, benzyl, alpha-methylbenzyl or alpha, alpha-dimethylbenzyl, and Z.sub.3 is hydrogen or cyano, or Z.sub.2 and Z.sub.3 together are one of the groups XV, XVI or XVII ##STR56## in which R.sub.6 is as defined above and R.sub.24 is hydrogen, methyl or ethyl and R.sub.25 is hydrogen, C.sub.1 -C.sub.18 alkyl, C.sub.3 -C.sub.8 alkenyl, cyclohexyl, C.sub.7 -C.sub.8 aralkyl or a group --CH.sub.2 --COOR.sub.26 or --CH.sub.2 --CH(R.sub.8)--O--R.sub.6, in which R.sub.26 is C.sub.1 -C.sub.18 alkyl and R.sub.6 and R.sub.8 are as defined above, and with the proviso that when R.sub.1, Z.sub.1 and Z.sub.3 are all hydrogen, Z.sub.2 cannot be --OR.sub.6 with the further proviso that each compound must have at least one R.sub.6 group.