The existence of monomeric phosphanylboranes of the type R2P-BR2 has been definitely established only recently. Nevertheless, Ph2P-BPh2 is known since 1961 [21, but it was not truly characterized until 1986 [31. Since then a number of other tetraarylphosphanylboranes have been rep~ rted [~-~]. Phosphanylboranes carrying alkyl substituents require sterically demanding groups such as the tert-butyl group on B or P atoms to be m~ nomerid~~~]. ...