Experimental evidence for comparable strength of phosphorus-sulfur and phosphorus-nitrogen p.pi.-bonding within the heteronaphthalenic framework: spectroscopic and structural studies of the 1,3,2-benzazathiaphospholium system as a cation and as neutral halides

Abstract

The new heteronaphthalenic framework 1,3,2-benzazathiaphospholium has been prepared as a free cation 1[NSP] and as the neutral chloride 2[NSPCl] and bromide 2[NSPBr] derivatives. The spectroscopic and structural (crystal data for C 6 H 5 AlCl 4 NPS: monoclinic, P2 1 /c, a=6.4773 (6) A, b=23.5434 (21) A, c=8.5101 (6) A, β=98.048 (7) o , Z=4) features of the cation are consistent with a hybrid of the corresponding dithia 1[S 2 P] and diamino 1[N 2 P] derivatives. In particular, the P-N and P-S bond lengths are very similar to those of the parent cations and represent experimental evidence for P-N and P-S pπ-bonding of comparable strength, in agreement with the theoretical π-bond energies. The neutral halides, 2-chloro-1,2,3-benzazathiaphosphole (crystal data for C 6 H 5 ClNPS: monoclinic, P2 1 /c, a=8.5607 (10) A, b=10.6948 (10) A, c=8.5994 (13) A, β=95.516 (11) o , Z=4) and 2-bromo-1,2,3-benzazathiaphosphole (crystal data for C 6 H 5 BrNPS: monoclinic, P2 1 /c, a=8.5345 (12) A, b=10.6990 (14) A, c=8.8213 (7) A, β=94.705 (8) o , Z=4) are isostructural and adopt dimeric structures, with long P-Z bonds