Acyl- und Alkylidenphosphane. XIX. Molekül- und Kristallstruktur des 2,4-Bis(dimethylamino)-1,3-diphenyl-1,3-diphosphetans

Acyl and Alkylidenephosphines. XlX. Molecular and Crystal Structure of 2,4-Bis (dimethyl-amino) ?1,3-diphenyl-l, 3-diphosphetane 2,4-Bis(dimethylamino)-1,3-diphenyl-1,3-diphosphetane 2a which is isolated as a byproduct in the synthesis of (E)-(dimethylamino)methylidene-phenylphosphine 1a crystallizes in the monoclinic space group P2₁/c. The dimensions of the unit cell determined at ?65 ± 5°C are: a = 1 004(1); b = 1 018(3); c = 1 873(2) pm; β = 105.15(8)°; Z = 4. As it is shown by a low temperature X-ray structure determination (R_g = 3.5%) the phenyl groups are placed above and the dimethylamino groups below the folded 1,3-diphosphetane ring; the molecule with its differently twisted substituents, however, deviates considerably from point symmetry mm2. The dihedral angle between the P1? C1n? P2 planes (n = 1 or 2) is found to be 153°. The relatively long Pn? C1n bond distances (187 to 191 pm) indicate a strained ring system; in solution 2a decomposes to some extent and forms monomeric 1a again. Further characteristic average bond distances and angles are: Pn? C4n (phenyl) 184; C? N 146 pm; P1? C1n? P2 93°; C11? Pn? C12 84° and Pn? C1n? Nn 116°.