A family of mixed (iminophosphoranyl)(selenophosphoranyl)methane ligands of general composition Ph(2)P(=Se)CH(2)P(=NR)Ph(2) have been synthesized by oxidation of Ph(2)PCH(2)P(=NR)Ph(2) with elemental selenium. In the presence of Et(3)N, these ligands react with [{RuCl(mu-Cl)(eta(6)-p-cymene)}(2)] to afford mononuclear Ru(II) species in which the resulting methanide anions adopt a tridentate coordination. Further deprotonation with KH generates carbenic ruthenium derivatives which participate, under remarkably mild conditions, in C-C coupling processes with isocyanides.