The invention is concerned with triazolopyridine compounds of formula (I), wherein R1, R2 , R3 and R4 are as defined in the description and in the claims, as well as physiologically acceptable salts thereof. These compounds inhibit PDEIOA and can be used as medicaments. The invention is concerned with triazolopyridine compounds of formula (I), wherein R1, R2 , R3 and R4 are as defined in the description and in the claims, as well as physiologically acceptable salts thereof. These compounds inhibit PDEIOA and can be used as medicaments. Disclosed is a neodymium based homogeneous phase rare earth catalyst and the neodymium based homogeneous phase rare earth catalyst is prepared by a process comprising the steps of: 1）in an inert solvent, preparing a mixture solution containing a neodymium carboxylate compound component a, a halogen-containing compound component c and a conjugated diene component d 2）adding an organo-aluminium compound component b to the mixture solution obtained from step 1） to obtain said neodymium based homogeneous phase rare earth catalyst wherein the organo-aluminium compound is selected from an alkylaluminium of a general formula AlR3 and an alkylaluminium hydride of a general formula AlHR2, in which R is a C1-C6 linear or branched alkane the molar ratio of each component in the catalyst is 1 : 5-30 : 2-10 : 35-65 of a : b : c : d. Disclosed also is another neodymium based homogeneous phase rare earth catalyst prepared by a process comprising the steps of: 1）in an inert solvent, preparing a mixture solution containing a neodymium carboxylate compound component a, a halogen-containing compound component c, a carboxylic acid component e and a conjugated diene component d 2）adding an organo-aluminium compound component b to the mixture solution obtained from step 1） so as to obtain the neodymium based homogeneous phase rare earth catalyst wherein the organo-aluminium compound is selected from an alkylaluminium of a general formula AlR3 a
