Sign inversion of 1J(207Pb13C) coupling constants and correlations between 1J(207Pb13C) and 1J(119Sn13C) values for comparable lead and tin compounds

Relative signs of 1J(207Pb13C) and 2J(207Pb1H) were determined for numerous methyllead derivatives by observing the 207Pb satellites in two‐dimensional (2D) 13C/1H heteroscalar correlated NMR spectra. The compounds studied include the species [R3Pb]Li (R = Me, 1a, Et 1b), Me3PbSiMe3 (2), [Me3PbBH3]Li, several alkenyltri‐methyllead compounds and some heterocyclics. Together with the linear correlation between 1J(207Pb13CMe) and 1J(119Sn13CMe) for the corresponding tin compounds, this enables the prediction of the absolute sign of 1J(207Pb13CMe). An analogous linear correlation 1J(207Pb13CC=)/1J(119Sn13CC=) exists which explains some apparently anomalous values reported in the literature, e.g. for [Ph3Pb]Li and for an intramolecular‐base‐stabilized plumbylene. The two coupling constants, 1J(207Pb13CMe), for the Me2Pb group in a 2,5‐dihydro‐1,2,5‐azoniaplumbaboratole are of opposite sign, giving the first example of this type of behaviour for any dimethyl element fragment. In the case of 2 the negative sign of 1J(207Pb29Si) [reduced coupling constant 1K(207Pb29Si) > 0] has been deduced from the tilt of the 207Pb satellites in the 2D 29Si/1H heteroscalar correlated NMR spectrum. A positive sign of 1J(207Pb11B) follows from the consistent trend observed for the reduced coupling constants 1K(M11B) and 1K(M13C) (M = 13C, 29Si, 119Sn, 207Pb) in the series of compounds [Me3MBH3]Li and Me4M, respectively.