Boronic disproportionation, stability

In the halide group the most active lone pair is found in the phosphortrihalides. The stability of the boron complexes AXZ.BXZ decreases in the sequence PXj -> AsXz SbX3, no antimony compounds being observed. The halides of the sulphur group do not form compounds at all it seems improbable that the only reason for this behaviour is the disproportionation of these halides. 

Because of its stability with regard to disproportionation, t-C4H9PF2 can be employed as a useful P(III) ligand, and a variety of complexes with transition metals, both zerovalent and in positive oxidation states, as well as those with boron acceptors, have been prepared. The preparation of a representative complex is described below. 

The cyclic dialkoxyborane 4,4,6-trimethyl-l,3,2-dioxaborinane (HBhg), the vinylboronic ester 2-ethenyl-4,4,6-trimethyl-l,3,2-dioxaborinane (vinylBhg) and the alkynylboronic ester 2-ethynyl-4,4,6-trimethyl-l,3,2-dioxaborinane were first reported in 1966-67 by Woods and coworkers. The authors stressed the high stability of HBhg towards disproportionation, as compared to the parents 1,3,2-dioxaborinane and 1,3,2-dioxaborolane, and its potential for the hydroboration of alkynes. In addition, the first reported o-metal-boron bond (rhodium) was prepared from HBhg. ... 

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