The present invention includes a composition of matter comprising a sulfide of a metal selected from Groups VIB, VIIB and VIII of the Periodic Tables, or mixtures thereof, and an aromatic, nitrogen-containing heterocyclic compound selected from the group consisting of tetrahydroquinoline, and the mono and diorgano substituted derivatives of tetrahydroquinoline. These compositions are useful as catalyst precursors. Indeed, upon heating at temperatures above 200.degree. C., the compounds are converted to active catalysts useful in polymerizing nitrogen-containing heterocyclic compounds.