Unsymmetrical 9-chloro-9-phosphafluorenes (dibenzophospholes) and 9-chloro-9-arsafluorenes (dibenzoarsoles) have been obtained by simple thermolysis of m-terphenyldichlorophosphines and -arsines in close to quantitative yields. The reaction temperatures are about 200 degrees C for the phosphines and 140 degrees C for the arsine, and the reactions are complete within 5 min. Alternatively, these compounds can be synthesized through an AlCl3-catalyzed Friedel Crafts type ring-closure reaction at low temperatures, but this method suffers from difficult workup procedures. The P(As)-Cl functionality is readily alkylated. Methylation of m-xylyl derivative 4 afforded 1-(3,5-dimethylphenyl)-6,8,9 trimethyl-9-phosphafluorene, 11. The latter compound formed the complexes 11, Fe(CO)(4), 12, and 11 center dot RuCl2(eta(6)-p-cymene), 13, indicating its good donor properties. The new compounds have been characterized by H-1, C-13 {1H}, and P-31 {H-1} NMR spectroscopy; mass spectrometry; and single-crystal X-ray crystallography in the case of 11, 12, and 13.