Diastereomeric pentacoordinate hypervalent stiboranes with an Sb−Fe bond {4a and 4b:  RfRfm*Sb*FeCp(CO)2 {Rf = o-C6H4C(CF3)2O-, Rfm* = o-C6H4C*(CF3)(Me)O-} were synthesized by the reaction of stiboranide anion, RfRfm*Sb*-Li+ (3-Li), with CpFeI(CO)2 in the presence of AgBF4. The carbonyl group of 4 was replaced with triphenylphosphine by irradiation with a tungten lamp to give a mixture of four diastereomers {5a−5d:  RfRfm*Sb*Fe*Cp(CO)(PPh3)}. Each of the diastereomers was separated by TLC, and the relative stereochemistry was determined by X-ray crystallographic analysis. The thermal equilibration from the pure diastereomer of 5 indicated that the isomerization took place through inversion (pseudorotation) at the central antimony atom. The pseudorotational barriers of 5 were much higher than those of Rf2Sb*Cl and RfRfm*Sb*(p-CH3C6H4). These results are consistent with the electron-donating properties of the group 8 transition metal fragment. Hypervalent stiboranes {6, Rf2Sb*Fe*Cp(CO)(PMe3); 7, Rf2Sb*Fe*Cp(CO)(PEt3)} were also prepared by similar procedures. The order of pseudorotational barriers [2 {Rf2Sb*Fe*Cp(CO)(PPh3)} (32.8, 33.2 kcal/mol) > 7 (32.5, 32.9 kcal/mol) > 6 (32.2, 32.7 kcal/mol)] suggests that the steric effect of the iron ligand also played a role. The pseudorotational barriers of the corresponding ruthenium compounds, RfRfm*Sb*RuCp(CO)2 (12a and 12b), were slightly higher than those of the corresponding iron compounds (4a and 4b).

Hypervalent pentacoordinate stiboranes with an Sb−group 6 element bond [Rf2Sb*MCp(CO)3 {Rf = o-C6H4C(CF3)2O-, M = Cr (2), Mo (3), W (4)}] were synthesized by the reaction of Rf2Sb*-Li+ (1-Li) with [CpM(CO)3]+BF4 -. X-ray crystallographic analysis of 2−4 showed that the geometry about the antimony atom is a distorted TBP structure with the CpM(CO)3 fragment at the equatorial site of the TBP. Diastereomeric antimony compounds RfRfm*Sb*MCp(CO)3 {Rfm* = o-C6H4C*(CF3)(Me)O-, M = Cr (10a,b), Mo (11a,b), W (12a,b)} were synthesized by similar procedures. Each of the diastereomers could be separated by flash column chromatography, and the relative stereochemistry was determined by X-ray analysis. The pseudorotational barrier of 11a at the central antimony atom was found to be very high (31.3 kcal/mol at 110 °C), showing the strong equatophilicity of the Mo fragment.