The title compound E 2 (2,4,6 tri tert butylphenylphosphinyl) 2 〔 N (ter t butyldimethylsilyl) N (p chrolophenyl)〕amino 1 (2,4,6 tri tert butyl phenyl)phosphacthylene(C 49 H 78 NClP 2Si, M r =806.65) was synthesized and characterized by X ray diffraction analysis. The crystal is monoclinic, space group P2 1/n with a=10.319(3), b=23.309(5), c=21.41(1) , β=99.64(5)°, V=5078(3) 3, Z=4, D c =1.05g/cm 3, F(000)=1760, μ =1.92cm -1 . Due to the steric hindrance from substituents around phosphaethylene, the P=C bond length is significantly longer than those observed in its analogues. The values of the three bond angles involved in the sp 2 hybridized carbon atom (C(1)) of the phosphaethylene are 133.4, 115.1 and 111.4° respectively, deviating significantly from the ideal value of 120°. In addition, although 5 sp 2 hybridized atoms (C(2), P(1), C(1), N and C(44)) are sequentially bonded in this molecule, no interaction is observed among the remaining pz orbits of these atoms on the string. The title compound E 2 (2,4,6 tri-tert-butylphenylphosphinyl) 2 [N (ter t butyldimethylsilyl) N (p chrolophenyl) amino 1 (2,4,6 tri-tert- butylphenyl) phosphacthylene (C 49 H 78 NClP 2Si , M r = 806.65) was synthesized and characterized by X-ray diffraction analysis. The crystal is monoclinic, space group P2 1 / n with a = 10.319 (3), b = 23.309 (5), c = 21.41 β = 99.64 (5) °, V = 5078 (3)  3, Z = 4, D c = 1.05 g / cm 3, F (000) = 1760, μ = 1.92 cm -1. Due to the steric hindrance from P values ​​for the three bond angles involved in the sp 2 hybridized carbon atom (C (1)) of the phosphaethylene are 133.4, 115.1 and 111.4 In addition, although 5 sp 2 hybridized atoms (C (2), P (1), C (1), N and C (44) are sequentially bonded in this molecule, no interaction is observed among the remaining pz orbits of these atoms on the string.