Organoantimony ring-chain equilibria:: Trapping of catena-tetrastibanes in cyclo-[Cr(CO)4(R′2Sb-SbR-SbR-SbR′2)] (R′ = Me, Ph; R = Me3SiCH2) and related complexes

Ring-chain equilibria between cyclo-(Me3SiCH2Sb)(n) (n = 4, 5) and R'Sb-4(2) (R' = Me, Ph) contain the catena-tristibanes R'Sb-2-SbR-SbR'(2) (1, R' = Me; 2, R' = Ph, R = Me3SiCH2) as the most abundant chain components. Addition of [nbdCr(CO)(4)] (nbd = norbornadiene) to the equilibrium mixture formed from cyclo-(Me3SiCH2Sb)(n) (n = 4, 5) and R'Sb-4(2) (R' = Me, Ph) gives cyclo-[Cr(CO)(4)(R'Sb-2-SbR-SbR-SbR'(2))] (3, R' = Me; 4, R' = Ph, R = Me3SiCH2), two complexes with catena-tetrastibane ligands. Reaction of 3 with [W(CO)(5)(thf)] (thf = tetrahydrofuran) leads to cyclo-[Cr(CO)(4)(Me2Sb-SbR-SbR-SbMe2)W(CO)(5)] = (R = Me3SiCH2) (5). The crystal structures of 3 and 5 have been determined by X-ray diffraction.