Synthesis and structures of hypervalent antimony compounds bearing an antimony-group 6 transition metal bond

Hypervalent pentacoordinate stiboranes with an Sb-group 6 element bond [Rf( 2)Sb*MCp(CO)(3) {Rf = o-C6H4C(CF3)(2)O-, M = Cr (2), Mo (3), W (4)}] were s ynthesized by the reaction of Rf(2)Sb(*-)Li(+) (1-Li) with [CpM(CO)(3)]+BF4 -. X-ray crystallographic analysis of 2-4 showed that the geometry about th e antimony atom is a distorted TBP structure with the CpM(CO)a 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 stereochemis try was determined by X-ray analysis. The pseudorotational barrier of 11a a t the central antimony atom was found to be very high (31.3 kcal/mol at 110 degreesC), showing the strong equatophilicity of the Mo fragment.