New and unusual co-ordination of main group elements

Abstract

There is considerable current interest in the chemistry of low coordinate main group elements the extensive development of which was highlighted at last year's Euchem Conference Psiblocs in Paris-Palaiseau (August 1988). This area has been stimulated by the isolation of low coordination compounds stabilised by the use of bulky groups, for example, Supermes, mes (see Chapters 3 and 4). Following the synthesis of 1,3,5 tris-trifluoromethyl benzene (ArB) by R.D. Chambers et al. (Chapter 1), and the facilities available to synthesise this material it seemed very worthwhile to study the influence of this substituent on low coordinate main group species. As a result, this group has been incorporated into phosphines, diphosphenes, phosphaalkenes, antimony and boron derivatives. Its involvement in other systems, for example borinium and phosphoranide species, and its incorporation into the cation associated with halo and pseudohalo borate anions, have also been examined. In particular, the low coordination chemistry of phosphorus has involved the synthesis, isolation and full characterisation of the new diphosphene (19) fprepared independently by Edelmann et al.]t and the unsymmetrical diphosphene (20) (Figure C1). The 2,6-bis(trifluoromethylphenyl) substituenthas been employed by Escudie et al.+