Abstract: A process for preparing heterocyclic carbenes of the ##STR1## in which R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are individually saturated or unsaturated, straight chain, branched or cyclic, unsubstituted or substituted C.sub.1 -C.sub.10 alkyl, C.sub.2 -C.sub.5 alkylidene, C.sub.2 -C.sub.5 alkylidine, C.sub.7 -C.sub.19 aralkyl or C.sub.6 -C.sub.14 alkyl groups, R.sup.3 and R.sup.4 can also stand for hydrogen or form jointly anellated, substituted or unsubstituted groups with between 3 and 7 carbon atoms and X stands for carbon or nitrogen, R.sup.3 being dropped if X is nitrogen comprising reacting azolium salts with a deprotonizing reagent in pure liquid ammonia or in pure organic amine or a mixture of liquid ammonia or an organic amine and an organic polar-aprotic solvent which are a plurality of temperature-sensitive carbenes are produced under mild reaction conditions at temperatures of between -75 and 0.degree. C.

Abstract: A complex of the formula?L.sub.a M.sub.b X.sub.c !.sup.n (A).sub.n Ias described in the application useful as homogenous catalysts.

Abstract: The preparation of aromatic olefins from haloaromatics and olefins (Heck reaction) is carried out in the presence of palladium complexes as catalysts, which complexes contain heterocyclic carbenes as ligands.

Abstract: A process for the hydroformylation of olefins and olefinically unsaturated compounds in the presence of cobalt or rhodium complexes which contain, as complexing ligands, heterocyclic carbenes and, if desired, further ligands.