Abstract: Selected novel phosphorus complexes of zerovalent iron containing phosphite ester ligands and, optionally diphosphine ligands, e.g., pentakis(trimethyl phosphite iron) and bis[ethylenebis(diphenylphosphine)] (trimethyl phosphite) iron, are disclosed. The compounds are prepared by various methods, by cocondensation of the vapors of iron and the ligand compound on a cold surface, e.g.,Fe + 5L .fwdarw. FeL.sub.5,by displacement reaction of the ligand with bis(cyclooctadiene)iron, by "wet-reduction" methods (preferred), e.g.,FeBr.sub.2 + 5L Na.sub.x Hg.sub.y .fwdarw. FeL.sub.5 + 2NaBr,and, where two diphosphines are desired, by displacement of ethylenes, e.g.,Fe(ethylene)(diphosphine).sub.2 + L .fwdarw. FeL(diphosphine).sub.2 + ethylene.The new compounds are useful as catalysts for the hydrocyanation of ethylene.