Geometrically Compelled Disilene with λ4‑Coordinate SiII Atoms

The first hypercoordinated disilene with the longest SiSi distance (2.623(1) Å) reported to date, the 5,6-bis­(amidinato silylenyl)­acenaphtene (amidinato = PhC­(NtBu)2) (1), is presented. It results from a spatially compelled double dative interaction between the two singlet silylene moieties, due to their close proximity. The dynamic behavior of the SiSi bond contraction and elongation in 1 predicted by quantum chemical calculations could be confirmed experimentally by variable temperature NMR spectroscopy. Compound 1 exhibits an ambivalent reactivity, reacting as disilene with ethylene, diphenylacetylene and benzophenone to give [2+2] cycloaddition products, but as bis­(silylene) toward Ni­(cod)2 (cod = cycloocta-1,4-diene) to form the corresponding bis­(silylene)­Ni0(η4-cod) complex.