The first hypercoordinated disilene with the longest Si=Si distance (2.623(1) angstrom) reported to date, the 5,6-bis(amidinato silylenyl)acenaphtene (amidinato = PhC((NBu)-Bu-t)(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)Ni-0(eta(4)-cod) complex.