Structural and nuclear magnetic resonance studies of short selenium–nitrogen bonds

SeCl4 reacts with Ph3PNSiMe3(2) by elimination of SiMe3Cl to form Ph3PNSeCl3(3), which is converted to (Ph3PN)2SeCl2(4) by a further mole of (2). Compound (4) may also be prepared from (2) and SeOCl2, or Se2Cl2; (4) reacts with SbCl5 to form [(Ph3PN)2SeCl]+[SbCl6]–(5). 2,4,6-Tri-t-butylaniline and SeOCl2 give chloro-N-(4,6-di-t-butyl-2-oxocyclohexa-3,5-dien-1-ylidene)selenamide, (7). Compounds (3),(4),(5), and (7), the previously reported diphenyl-N-(p-toluenesulphonyl)selenimide, (1), and 5,6-dimethyl-2,1,3-benzoselenadiazole, (8), have been studied by 77Se n.m.r.; the crystal structures of (1), (3), (4), and (7) have been determined by X-ray diffraction. The Se–N bond lengths of 1.787(6), 1.680(4), 1.735(4), and 1.766(4)Å all indicate significant Se–N multiple bonding when compared with Se–N bonds from the literature, but curiously the longest of the four is in (1), the only structure containing a formal double bond. Although bond length alternation indicates that the quinone type resonance extreme predominates for (7), the Se–N and Se–O distances are shorter than in an analogous compound, N-(3,5-dimethyl-2-oxocyclohexa-3,5-dien-1-ylidene)phenylselenamide, the Se–O distance being reduced by 0.5 Å to 2.079(3)Å.