Abstract: Novel chemical compounds which comprise tetramethyldiphosphinomethane of the formula:(CH.sub.3).sub.2 P--CH.sub.2 --P(CH.sub.3).sub.2and methyllithium-dimethylphosphine of the formula:LiCH.sub.2 --P(CH.sub.3).sub.2,the latter being an intermediate product. Methyllithium-dimethylphosphine is made by reacting a solution of trimethylphosphine with a solution of alkyllithium in an inert solvent with the exclusion of air and moisture, filtering the resulting white precipitate, washing it with the inert solvent, and drying the washed material. Tetramethyldiphosphinomethane is made by reacting, with agitation, a suspension of methyllithium-dimethylphosphine, or dilithiomethane of the formula Li(CH).sub.2 or magnesiomethane of the formula MgCH.sub.2 in an organic solvent with dimethylchlorophosphine and distilling the resulting reaction mixture.