8] Crystal structure analysis of 6 : monoclinic. P2,/a, a = 17.919(18). b = 16.238(16), c = 34.53(3) A, j3 = 90.83(6)", V = 10047 A3, Z = 8; 7501 reflections (I> 2 4 four-circle diffractometer, Mo,, radiation, w scan), R = 0.065, R, = 0.059 (As, Si, 0, C anisotropic, H in calculated positions, isotropic temperature factors, phenyl rings as rigid groups, 921 parameters).'"' [9] The arsaalkenes 8 and 9 were characterized by 'H NMR as well as " C NMR spectroscopy and also mass spectrometry. The 1,3,2,4-dioxadisilethane 7 [a(' %) = -6.38; MS (EI, 70 eV): m/z 900 ( M i , 84(%), 435(Is,SiH+, IOO)] is identical with the product from the oxidation of