N-Triorganostannyl‐substituted pyrroles and indoles and N-trimethylstannylcarbazole: determination of signs of coupling constants and isotope‐induced chemical shifts 1Δ1415N(119Sn)

Abstract

N-Triorganostannyl (R3Sn)-substituted pyrroles (1) and indoles (2) [R=Me (a), Et (b), tBu (c)], N-trimethylstannyl-carbazole (3), N-trimethylstannyl-2,5-dimethylpyrrole (1d), the corresponding silicon and lead derivatives [1d(Si) and 1d(Pb)] and N-trimethylstannyl-2-methylindole (2d) were prepared and studied by multinuclear magnetic resonance (1H, 13C, 15N, 29Si, 119Sn and 207Pb NMR). The absolute signs of numerous coupling constants nJ(119Sn,13C) and 1J(119Sn,15N) (<0) were determined by appropriate 2D heteronuclear shift correlations of the type 13C/1H and 15N/1H. Precise measurement of the coupling constants 1J(119Sn,15N) from 119Sn NMR spectra by using Hahn-echo extended (HEED) polarization transfer pulse sequences enabled one to obtain isotope-induced chemical shifts 1Δ14/15N(119Sn) at natural abundance of 15N. The 1Δ14/15N(119Sn) data become more negative with increased branching of the substituent R at the tin atom and with stronger steric interactions. The latter effect is also evident from δ119Sn values and changes in the magnitude of the coupling constants 1J(119Sn,13C) or 1J(119Sn,15N). © 1998 John Wiley & Sons, Ltd.