2-tert-Butyl-2,2'-spirobi(1,3,2-benzodioxaphosphole)

Abstract

C6H402)2PC(CH3)3, orthorhombic, P212121, a= 13.223 (3), b = 6.783 (1), c = 16.832 (5) A, Mr= 304.3, Z = 4, D m = 1.33, D x -- 1.34 g cm -3, g(Mo Ka) = 2.0 cm-~; final R = 0.07. The stereochemistry of the pentacoordinate P atom can be described as an 87% rectangular pyramid with the tert-butyl group at the apical site. The two trans basal angles O-P-O are 154.9 and 147.0 ° . Preliminary results have been given (Wunderlich, Third European Crystallographic Meet- ing, Zurich, Switzerland (1976), Abstract 0 54 D). Introduction. The preparation of the title compound is described by Wieber, Foroughi & Klingl (1974). The crystals, received from these authors, were very air sensitive and had to be sealed in capillaries for X-ray investigations. Systematic absences were unique for the space group P2~2~2~. The intensities of all 1564 symmetry-independent reflections up to 20 = 50 ° were measured on a computer-controlled diffractometer (Syntex P21) with Mo Ka radiation, a crystal mono- chromator and a 0/20 scan mode. From this set five reflections had intensities too high with respect to dead- time losses of the counter and, in addition, a series of 12l reflections had to be removed later because the operation of the shutter had failed. From the resulting 1543 reflections, 1210 were classified as observed (F o > 2.5aF) and were used for the structure deter- mination. The phase problem was solved from the Patterson function, and the solution completed by Fourier syntheses. The eight H atoms connected to the benzene rings could be located in a difference synthesis, but the nine H atoms of the tert-butyl group could be found from a subsequent difference synthesis only with difficulty. Due to high thermal motion in this group their positions remain questionable. During the final refinement with anisotropic thermal parameters for all non-hydrogen atoms, fixed temperature factors for the H atoms of the benzene rings and fixed positional and thermal parameters for the H atoms of the tert-butyl group 214 parameters were refined to R -- 0.071 (0.094) and R w = 0.068 (0.070) for the ob-