CRYSTALLOGRAPHICALLY DETERMINED SE=O AND P=O INTERACTIONS IN TRIS(2,4-DIMETHOXYPHENYL) PHOSPHINE SELENIDE AND THE 2,4,6-TRIMETHOXY ANALOG - CORRELATIONS OF P-SE BOND LENGTHS WITH SE-77 NMR DATA

(2,4-Dimethoxyphenyl)3PSe crystallizes in the monoclinic space group P21/n with four molecules in the unit cell having dimensions of a = 9.0660(1), b = 17.2102(3), c = 17.2475(3) Å, β = 98.3(2)° and refined to R = 5.2% for 1258 observed reflections. (2,4,6-Trimethoxyphenyl)3PSe is orthorhombic, space group P212121 with four molecules in the unit cell a = 18.2983(5), b = 12.3716(1), c = 12.4696(1) Å and refined to R = 6.4% for 1229 observed diffractometer data. In both cases the rings are orientated so that weak PO interactions take place between one of the o-methoxy groups and phosphorus. Similar interactions between selenium and oxygen are also found. These interactions may account for the significant deshielding of the selenium atom in these compounds compared with related triarylphosphine selenides as shown by 77Se NMR data. © 1990.