From the NMR spectroscopic data 6 cannot with certainty he dediced to he the dimer (eightmembered ring) or the monomer (four-membered ring). The mass spectrum (CI. + 30-C) exhibits a peak at m / z = 299 ([Me,P-C(SiMe,)-PMe,-P-PMe,]+), which isassigned to a fragment ion of the dimer. 'lP{ 'HI NMR of 6 (C,D,. + 20°C): 6PA = -109.53 (1, 250.7 Hz). 6P, = +7.86 (d, 250.7 Hz).
[lo] a) 7: Single CryStdk by recrystallirdtion from pentane; C,,H,,P,Si,;
Enraf-Nonius-CAD4 diffractometer; Mo,, radiation; programs SHELXTL Plus Rel. 4.1. SHELXL-93, and DIFABS; structure solution by direct methods; triclinic; Pi; u = 8.556(1), b =13.633(1). c =14.137(1) A, 1 = 88.11(1r. , B = 89.60(1)'. ; =72.20(1)'. V =1569.2(2)A3. Z = 2, pca,cd =1.106gcm-'. p = 0.376mm-', 0-0 scan, scan range 6"<20<54". 6682 independent reflections, 5602 observed reflections with F0>4u(F0); 276 parameters; R = 0.031 and wRZ = 0.0784 for Fo > 4a(F0), R = 0.042 and wR2 = 0.085 for all data; maximum residual electron density 0.247 e k 3 . (b) Further details of the crvstal structure investieations 1993. 459, 95.