REACTION OF METHANOL WITH DIPHENYLANTIMONY(V) TRIHALIDES - CRYSTAL-STRUCTURE OF [SBPH2BR2(OME)CENTER-DOT-MEOH]2

A re-examination of the reaction between diphenylantimony trichloride and methanol showed that the initial product is a methanol adduct of t he monomethoxide, SbPh2Cl2(OMe), rather than the oxide (SbPh2Cl2)2O, w hich is a hydrolysis product formed during recrystallisation. The corr esponding tribromide, and the mixed halides, SbPh2Br3-nCln where n = 1 or 2, react similarly with methanol, losing a bromine atom to give so lvated monomethoxy products. X-Ray diffraction analysis revealed that SbPh2Br2(OMe) crystallises as a centrosymmetric dimer, incorporating t wo molecules of methanol, which are attached via strong hydrogen bonds to the oxygen atoms of the methoxy groups. Co-ordination of the metha nol oxygen to a symmetry-related antimony atom completes the distorted -octahedral co-ordination about antimony and forms a central eight-ato m ring system in the chair conformation. Two unusual features are the similarity of the two Sb-O distances [2.101 (4) and 2.121 (4) angstrom , even though the former is formally a normal sigma bond and the latte r a donor linkage, and the presence of a weak pi-arene ... H-C hydroge n bond, which probably accounts for the orthogonality of the phenyl gr oups at antimony.