The present invention relates to ligands and catalyst systems for the 
hydroformylation of short and 
long chain olefins, preferably for the 
hydroformylation of ally 
alcohol producing 4-hydroxybutyraldehyde. The ligands disclosed herein are all-trans phosphinomethyl-
cyclobutane ligands, such as, for example, all-trans-1,2,3,4-
tetra[bis-(3,5-xylyl)phosphinomethyl]-
cyclobutane. The catalyst systems comprise these all-trans phosphinomethyl-
cyclobutane ligands in combination with an organometallic 
rhodium complex such as, e.g., (acctylacetonato)-dicarbonyl-
rhodium (I). The ligands and catalyst systems of the present invention may be employed in the 
hydroformylation of olefins, in particular in the hydroformylation of allylalcohol, and provide improved selectivity and high reaction yields. wherein R1 is 
alkyl, preferably methyl, ethyl or propyl, R2 is H or an 
alkoxy group, R3 and R4, independently of one another, CH2OR1, CH2O-aralkyl, CH2OH,CH2—[P(3,5-R1,R1-4-R2-phenyl)2] or CH2O—(CH2—CH2—O)m—H (with m being an integer between 1 and 1.000).