Isotope-induced chemical shifts1?12/13C(29Si) and57Fe NMR of organosubstituted 2,5-dihydro-1,2,5-azasilaboroles, a silole and their tricarbonyliron complexes

2,5-Dihydro-1,2,5-azasilaboroles (1) (cyclic heterodienes) readily form tricarbonyliron complexes (3) and both are compared with a silole (2) and its tricarbonyliron complex (4). The compounds 1–4 were studied with respect to isotope-induced chemical shifts 1Δ12/13C(29Si). The data set indicates that the interpretation of 1Δ12/13C(29Si) is not straightforward. Although there may be a crude correlation between 1Δ12/13C(29Si) and the magnitude of |1J(29Si,13C| within each class of compounds [e.g., in the series Me4 −nSi(CCMe)n (n = 0, 1, 2, 3, 4)], a direct relationship between different classes is not apparent, even for different Me groups linked to the same silicon atom (3, 4). 57Fe NMR (16.2 MHz) measurements are reported for the first time, using standard NMR equipment and ca 0.5 M solutions in 5 mm tubes. The 57Fe nuclear shielding in the heterodiene complexes is reduced by 500–600 ppm with respect to that of the silole complex (δ57Fe = +241.2).