Synthesis and structural comparison of triaryl(sulfonylimino)pnictoranes

Triarylphosphanes 1 (Ar(3)P; Ar = Ph, 4-MeC(6)H(4)), triphenylarsane (2), and triarylstibanes 3 (Ar(3)Sb; Ar = 2-MeC(6)H(4), 2-MeOC(6)H(4)) reacted with trifluoromethanesulfonamide (7a) in the presence of equimolar diethyl azodicarboxylate to afford the corresponding triaryl(sulfonylimino)pnictoranes [Ar(3)M=NSO(2)CF(3); 8 (M = P), 9 (M = As), 10 (M = Sb)]. The Kirsanov-type reaction of triarylantimony dichlorides 5 (Ar(3)SbCl(2); Ar = 2-MeC(6)H(4), 2-MeOC(6)H(4)) and triarylbismuth dichlorides 6 (Ar(3)BiCl(2); Ar = 2-MeC(6)H(4), 2-MeOC(6)H(4), 2,4,6-Me(3)C(6)H(2)) with sulfonamides 7 (H(2)NSO(2)R; R = CF(3), 4-MeC(6)H(4), Me) in the presence of 2 equiv of potassium tert-butoxide yielded triaryl(sulfonylimino)-lambda(5)-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, SO(2) asymmetric stretching absorptions (nu(SO2)) were observed at lower wavenumbers as compared to those of phosphorus counterparts 8. The difference in frequency (Deltanu(SO2)) 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-lambda(5)-bismuthanes 11 oxidized alcohols to carbonyl compounds.