Isolation of an Annulated 1,4-Distibabenzene Diradicaloid.

The first 1,4-distibabenzene-1,4-diide compound [(ADC)Sb] 2 (5) based on an anionic dicarbene (ADC) (ADC=PhC{N(Dipp)C} 2 , Dipp=2,6-iPr 2 C 6 H 3 ) is reported as a bordeaux-red solid. Compound 5, featuring a central six-membered C 4 Sb 2 ring with formally Sb I atoms may be regarded as a base-stabilized cyclic bis-stibinidene in which each of the Sb atoms bears two lone-pairs of electrons. 5 undergoes 2 e-oxidation with Ph 3 C[B(C 6 F 5 ) 4 ] to afford [(ADC)Sb] 2 [B(C 6 F 5 ) 4 ] 2 (6) as a brick-red solid. Each of the Sb atoms of 6 has an unpaired electron and a lone-pair. The broken-symmetry open-shell singlet diradical solution for (6) 2+ is calculated to be 2.13 kcal mol -1 more stable than the closed-shell singlet. The diradical character of (6) 2+ according to SS-CASSCF (state-specific complete active space self-consistent field) and UHF (unrestricted Hartree-Fock) methods amounts to 36 % and 39 %, respectively. Treatments of 6 with (PhE) 2 yield [(ADC)Sb(EPh)] 2 [B(C 6 F 5 ) 4 ] 2 (7-E) (E=S or Se). Reaction of 5 with (cod)Mo(CO) 4 affords [(ADC)Sb] 2 Mo(CO) 4 (8).