New square-pyramidal organoantimony(V) compounds; crystal structures of (biphenyl-2,2′-diyl)phenylantimony(V) dibromide, dichloride and diisothiocyanate, Sb(2,2′-C12H8)PhX2 (X = Br, Cl or NCS), and of octahedral SbPh(o-O2C6Cl4)Cl2 ·OEt2

Abstract

Oxidative addition between (biphenyl-2,2′-diyl)phenylantimony(III), Sb(2,2′-C 12 H 8 )Ph 1 and Br 2 or SO 2 Cl 2 gave Sb(2,2′-C 12 H 8 )PhBr 2 2 and Sb(2,2′-C 12 H 8 )PhCl 2 3, respectively, while the corresponding fluoride Sb(2,2′-C 12 H 8 )PhF 2 4 and the thiocyanate Sb(2,2′-C 12 H 8 )Ph(NCS) 2 5 were obtained by metathesis reactions between 3 and KF and KSCN, respectively. Compounds 2 and 3 are isostructural but, in contrast to the closely related SbPh 3 X 2 species, individual molecules have square-pyramidal geometry. Again in contrast to SbPh 3 X 2 compounds, secondary antimony–halogen interactions trans to the apical carbon atom lead to solid-state dimers, implying Lewis acidity at antimony. Antimony in the thiocyanate 5 showed similar square-pyramidal geometry with N-bonded thiocyanate groups but bridging by one thiocyanate again gives dimers in the solid. Oxidative addition between SbPhCl 2 and tetrachloro-ortho-benzoquinone in ether solution gave the tetrachlorocatechol analogue of 3 as a six-co-ordinate ether solvate, SbPh(o-O 2 C 6 Cl 4 )·OEt 2 6. If the weak bond to ether is ignored, antimony again has square-pyramidal geometry but formation of the adduct again points to antimony Lewis acidity. A non-solvated substituted catecholate, SbPh(o-O 2 C 6 H 2 Bu t 2 -3,5)Cl 2 8, was also synthesized but crystals suitable for X-ray diffraction could not be obtained.