The prolonged photo-Arbuzov reaction (3 weeks, Hg lamp) of 1,3,5-trichloro-benzene with a large excess of trimethyl phosphite (as a solvent) at 508 gives moderate yields of dimethyl (3,5-dichlorophenyl)phosphonate (1; 14.5%), tetramethyl (5-chloro-1,3-phenylene)bis[phosphonate] (2; 35.4%), and hexamethyl (benzene-1,3,5triyl)tris[phosphonate] (3; 30.1%). The products can be separated by fractional distillation. Acid hydrolysis of the esters gives almost quantitative yields of the corresponding phosphonic acids 4 ± 6. Reduction of the esters 1 ± 3 by LiAlH 4 in tetrahydrofuran affords the primary phosphines (3,5-dichlorophenyl)phosphine (7; 46.5%), (5-chloro-1,3-phenylene)bis[phosphine] (8; 34.5%) and (benzene-1,3,5-triyl)tris[phosphine] (9; 25.2% yield). In the crude reduction products from 2 (preparation of 8) and from 3 (preparation of 9), (3chlorophenyl)phosphine and (1,3-phenylene)bis[phosphine], respectively, are observed as by-products. All compounds are characterized by standard analytical, spectroscopic, and (for 1, 7, and 8) structural techniques. The arrangement of the molecules in the crystal structures of 7 and 8 suggest that H-bonding between the primary arylphosphines is virtually insignificant for the packing of the components. This is in marked contrast to the importance of H-bonding for the supramolecular chemistry of arylamines. The new primary polyphosphines and polyphosphonic acids are to be employed in the construction of extended arrays.