The present invention relates to a process for the preparation of a compound of formula (I), wherein X is —CH2—, —CH2—CH2—, —CH2—CH2—CH2— or —CH2—CH2—CH2—CH2—; Y1 is —CH2—; —CH2—CH2— or —NH—; Y2 is NHR7 or SH; wherein R7 is hydrogen, C1-C4alkyl or phenyl; R-1 and R2, independently from each other, represent aliphatic or aromatic groups; R3 and R4, independently from each other, represent aliphatic or aromatic groups; R5 and R6 are each hydrogen or represent together with the carbon atoms to which they are bonded, a phenyl ring; which process comprises reacting a compound of formula II [RuCI2(R8)n]m (II), wherein n is 1 and m is >1 which represents a polymeric structure if R8 is a molecule containing two alkene or alkyne moieties coordinating in an hapto-2 coordination mode to the metal; or n is 4 and m is 1 if R8 is a nitrogen, oxygen or sulfur containing molecule in which said nitrogen, oxygen or sulfur coordinate to the metal; in the presence of an inert solvent which boiling point is from 1 12° C. to 165° C. with a compound of formula (III), wherein R5, R6, Y1 and Y2 are as defined under formula I, and a phosphane of formula IV R3R4P—X—PR1R2 (iv), wherein R1, R2, R3, R4 and X are as defined under formula I.