The dimeric organoantimony(III) oxide (ArSbO) 2 (Ar ) NCN chelating ligand, C 6 H 3 -2,6-(CH 2 NMe 2 ) 2 ) was obtained by the reaction of the parent ArSbCl 2 compound with KOH. This oxide is able to bind carbon dioxide with formation of the monomeric, air-stable carbonate ArSbCO 3 . In turn, carbon dioxide can be easily eliminated from this carbonate by prolonged heating to 130 °C to recoVer (ArSbO) 2 .

The reaction of N,C,N‐chelated stibinidene ArSb (1) (Ar=C6H3‐2,6‐(CH=NtBu)2) with selected N‐alkyl/aryl‐maleimides RN(C(O)CH)2 (R=Me, tBu, Ph) gave the addition products with bridged bicyclic [2.2.1] structure containing an antimony atom at the bridgehead position, fused with a 6‐membered benzene and a 5‐membered N‐alkyl/aryl‐pyrrolidine ring. These compounds were completely characterized. More importantly, additional studies showed that these reactions are reversible in solution, thereby representing an unprecedented reversible activation of a C=C bond by an antimony(I) compound.

The reactions of the dimeric organoantimony(III) oxide [LSbO]2 (3), containing the NCN chelating ligand L (L = C6H3-2,6-(CH2NMe2)2) with trifluoroacetic acid and trifluoromethanesulfonic acid gave the unprecedented organoantimony hydroxides LSb(OH)(X) (X = CF3CO2 (6), CF3SO3 (7)). On the other hand, analogous reactions with acetic acid and tetrafluoroboric acid led to a polar group exchange, providing the compounds LSbX2 (X = F(4), CH3CO2 (5)). Analogously, the organobismuth oxide [LBiO]2 (8) gave the acetate LBi(O2CCH3)2 (9) in its reaction with acetic acid but the hydroxide LBi(OH)(CF3SO3) (10) was obtained when trifluoromethanesulfonic acid was used. All compounds were characterized with the help of elemental analysis, ESI mass spectrometry, and 1H and 13C NMR spectroscopy, and their molecular structures were determined by X-ray diffraction techniques. The molecular structures of hydroxides 6 and 7 may be described as being built up from the organoantimony cation [LSb(OH)]+ effectively stabilized by the NCN ligand L and the counteranion X−, which is connected to the terminal Sb−OH moiety through the hydrogen bond Sb−OH···X. The organobismuth analogue 10 forms the weakly bonded dimeric units LBi(μ-OH)2BiL, and the triflate anions are connected to the bridging OH moieties via the hydrogen bonds as well as to the bismuth centers through Bi−O interactions, leading to an infinite chain supramolecular structure of 10.

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