The organolanthanoid derivatives R2M (R C6F5, M Yb or Eu; R o-HC6F4 or PhCC, M Yb) have been prepared by reaction of the corresponding diorganomercury compounds with ytterbium or europium metal in tetrahydrofuran at room temperature, and (o-HC6F4)2Yb has been obtained by an analogous reaction at 0°C. The compounds were identified by determination of the amounts of polyfluoroarene or phenylacetylene and lanthanoid ions formed on acidolysis of the filtered reaction mixtures. Reaction of samarium with bis(pentafluorophenyl)mercury and of ytterbium with bis(2,3,4,5-tetrafluorophenyl) mercury at room temperature gives more complex products including RMF2, MF2 and RMF derivatives (R C6F5, M Sm; R o-HC6F4, M Yb), polyfluoropolyphenyls, and more complex organometallic species. These are considered to be derived from decomposition of initially formed (C6F5)2Sm, (C6F5)3Sm, and (o-HC6f4)2Yb derivatives. The decomposition paths include fluoride elimination to give polyfluorobenzynes, reduction of polyfluoroaryl groups by lanthanoid(II) species, and hydrogen abstraction from tetrahydrofuran.