Core excitation spectroscopy of stable cyclic diaminocarbenes, -silylenes,and -germylenes

A number of tert-butyl-substituted, cyclic, saturated and unsaturated diami nocarbene, diaminosilylene, and diaminogermylene compounds were investigate d using inner shell electron energy loss spectroscopy (ISEELS) and ab initi o calculations. These compounds, each of which contains a divalent group 14 element (C, Si, Ge), are of particular interest since they are stable inde finitely, and thus, they are readily accessible for detailed spectroscopic analysis. The C 1s and N 1s spectra of the hydrogenated tetravalent analogu es of the saturated carbene, of di-tert-butyldiazabutadiene, and of di-tert -butyldiazabutane were also obtained to assist with spectral interpretation . Our analysis shows that there is significant pi-allyl delocalization over the N-E-II-N fragment in all three species. Further, in the unsaturated sp ecies there is additional aromatic delocalization. Both theory and experime nt indicate that the divalent center of the carbene is qualitatively differ ent from that in the germylenes or silylenes.