The invention relates to hydrocarbon-soluble halogen or thiolate/magnesium exchange reagents of the general formula R1MgR11-n(OR3)n.LiOR2.(1−n)LiOR3.aDonor in which: R1 is a C1-C8 alkyl and OR2 as well as OR3 are same or different and represent primary, secondary, or tertiary alkoxide residues having 3 to 18 carbon atoms, wherein R2 and/or R3 can for their part contain an alkoxy substituent OR4; a assumes a value of 0 to 2, n assumes a value between 0 and 1, and the donor is an organic molecule containing at least 2 nitrogen atoms.