Synthesis and Structural Comparison of Triaryl(sulfonylimino)pnictoranes

Triarylphosphanes 1 (Ar3P; Ar = Ph, 4-MeC6H4), triphenylarsane (2), and triarylstibanes 3 (Ar3Sb; Ar = 2-MeC6H4,
2-MeOC6H4) reacted with trifluoromethanesulfonamide (7a) in the presence of equimolar diethyl azodicarboxylate
to afford the corresponding triaryl(sulfonylimino)pnictoranes [Ar3MNSO2CF3; 8 (M = P), 9 (M = As), 10 (M =
Sb)]. The Kirsanov-type reaction of triarylantimony dichlorides 5 (Ar3SbCl2; Ar = 2-MeC6H4, 2-MeOC6H4) and
triarylbismuth dichlorides 6 (Ar3BiCl2; Ar = 2-MeC6H4, 2-MeOC6H4, 2,4,6-Me3C6H2) with sulfonamides 7 (H2NSO2R;
R = CF3, 4-MeC6H4, Me) in the presence of 2 equiv of potassium tert-butoxide yielded triaryl(sulfonylimino)-λ5-stibanes 10 and -bismuthanes 11, respectively. The ortho-substitution in aryl ligands of 10 and 11 has been found
to bring about considerable kinetic stabilization of the reactive SbN and BiN bonds. A structural comparison
was made for a series of triaryl(sulfonylimino)pnictoranes 8−11 by IR spectroscopy and X-ray crystallography. In
the IR spectra of 9−11, SO2 asymmetric stretching absorptions (νSO2) were observed at lower wavenumbers as
compared to those of phosphorus counterparts 8. The difference in frequency (ΔνSO2) from 8 increased progressively
as the pnictogen element being utilized moved down the group 15 column on the periodic table. X-ray crystallographic
analyses of eight of the triaryl(sulfonylimino)pnictoranes prepared confirmed the increasing single-bond character
of the MN bond, with the contribution from the canonical structure M+NS(O)O- increasing in importance
in the order P < As < Sb < Bi. Among all triaryl(sulfonylimino)pnictoranes examined, only imino-λ5-bismuthanes 11
oxidized alcohols to carbonyl compounds.