TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Educts: The (hetero)aromatic halogen compounds have 2-40C atoms and are optionally substituted by 1-20C linear, branched or cyclic alkyl or alkoxy group(s) (in which non-adjacent CH2 group(s) may be replaced by O, C=O or carboxy), (un)substituted 2-20C (hetero)aryl, F, CN or NO2.Preferred compounds are optionally substituted derivatives of benzene, naphthalene, anthracene, pyrene, biphenyl, fluorene, spiro-9,9'-bifluorene, phenanthrene, perylene, chrysene, naphthacene, pentacene, triptycene, pyridine, furan, thiophene, benzothiadiazole, pyrrole, quinoline, quinoxaline, pyrimidine or pyrazine.Preferred Catalysts: The catalyst is produced in advance or in situ. The group 1 ligands contain main group 5 or 6 heteroatoms other than phosphorus (P), preferably nitrogen (N) and/or oxygen (O). The group 2 ligands have two eta1-co-ordinations to Ni, each through a heteroatom, and/or at least one, preferably two eta2-co-ordinations to Ni through a pi-system. These ligands preferably contain alkyne and/or alkene groups.Preferred Solvents: Solvents with low polarity are used, e.g. aliphatic and aromatic hydrocarbons, especially pentane, cyclohexene, toluene or xylene. These may be mixed with inert, dipolar solvents, e.g. DMF, N,N-dimethylacetamide, N-methylpyrrolidin-2-one, tetramethylurea, dimethyl sulfoxide or sulfolane. A mixture of DMF and toluene is preferred. EXAMPLE - Manganese (Mn, 0.11 g, 2 mmole) was mixed with a solution of nickel bromide (NiBr2, 200 mg, 0.9 mmole) in dimethylformamide (DMF, 5 ml) at room temperature. On slow addition of a ligand solution of bipyridine (150 mg, 0.96 mmole) and COD (1,5-cyclooctadiene, 0.12 ml, 1 mmole) in toluene (15 ml), the solution became deep violet after 5-10 minutes. This was stirred vigorously overnight at room temperature, giving a catalyst solution that was stable for several weeks under argon. Mn (1.6 g, 0 mmole) and the catalyst solution (11 ml) were stirred under argon at 50 degrees C for 10 minutes, when the mixture remained stable violet. Then, 2-bromotoluene (3.4 g, 20 mmole) in toluene (50 ml) was added. The mixture became red and was stirred at 50 degrees C for 48 hours (until the solution became violet again). After cooling to room temperature, the solution was filtered and evaporated to dryness and the residue was worked up and purified by chromatography, giving 99.9% pure dimer, 2,2'-dimethyl-biphenyl in a yield of 1.7 g (94%).