Synthesis, Structure, and Reactions of (Acylimino)triaryl-λ5-bismuthanes:  First Comparative Study of the (Acylimino)pnictorane Series

• Published in: Journal of the American Chemical Society 2001-11, Vol.123 (44), p.10954-10965
• Main Authors: Matano, Yoshihiro, Nomura, Hazumi, Suzuki, Hitomi, Shiro, Motoo, Nakano, Haruyuki
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja003623l

The synthesis, structure, and reactions of (acylimino)triaryl-λ5-bismuthanes and a comparative study of the structure and reactivity of a series of (acylimino)pnictoranes are reported. Treatment of ortho-substituted triarylbismuth dichlorides 1 (Ar3BiCl2; Ar = 2-MeC6H4, 2-MeOC6H4, 2,4,6-Me3C6H2) with amides 2 (H2NCOR; R = CF3, CCl3, 3,5-(CF3)2C6H3) in the presence of 2.2 equiv of KO-t-Bu in dichloromethane afforded (acylimino)triaryl-λ5-bismuthanes 3 (Ar3BiNCOR) in yields of 77−96%. The ortho-substituted aryl ligands and the electron-withdrawing N-substituents afford kinetic and thermodynamic stabilization, respectively, to the reactive BiN bond. The structures and properties of a series of (acylimino)pnictoranes (Ar3MNCOR and H3MNCOCF3; M = P, As, Sb, Bi) are compared by IR and 13C and 15N NMR, X-ray crystallography, and ab initio molecular orbital calculations. It was found that the contribution of the M+−NC−O- canonical form becomes more prominent and the single-bond character of the MN bond increases progressively as the pnictogen atom becomes heavier. The BiN bond of (acylimino)-λ5-bismuthanes 3 possesses a highly polarized single-bond character, probably due to the differences in orbital size and electronegativity between the bismuth and nitrogen atoms. Thermal decomposition of (aroylimino)triaryl-λ5-bismuthane 3f (o-Tol3BiNCOAr; Ar = 3,5-(CF3)2C6H3) produces a gel in dry conditions or aniline 12 (ArNH2) in slightly wet conditions with a good recovery of tris(2-methylphenyl)bismuthane (4a). It is likely that the aryl isocyanate 13 (ArNCO) is produced during the thermolysis via a concerted C → N migration of the Ar group with an elimination of the triarylbismuthonio group as bismuthane 4a. (Acylimino)triaryl-λ5-bismuthanes 3 oxidize 1,1,2,2-tetraphenylethanediol, benzenethiol, methanol, and ethanol to benzophenone, diphenyl disulfide, methyl formate, and acetaldehyde, respectively, in two different reaction pathways depending on the structure of the substrates. Compound 3d (o-Tol3BiNCOCCl3) transfers the nitrenoid moiety to triphenylphosphane, triphenylarsane, and tris(2-methylphenyl)stibane to give the corresponding (acylimino)pnictoranes (Ar3MNCOCl3; M = P, As, Sb) and 4a, suggesting that 3d is thermodynamically much less stable than their lighter pnictogen counterparts. The copper-catalyzed decomposition of 3 (o-Tol3BiNCOR) afforded N-acyl-o-toluidines 18 (o-TolNHCOR) via a Bi → N migration of the tolyl group. The observed reactivities o