Controlled Synthesis of Oligomers Containing Main‐Chain B(sp(2))‐B(sp(2)) Bonds

A number of novel alkynyl‐functionalized diarylbis(dimethylamino)diboranes(4) are prepared by salt metathesis, and the appended alkynyl groups are subjected to hydroboration. Their reactions with monohydroboranes lead to discrete boryl‐appended diborane(4) species, while dihydroboranes induce their catenation to oligomeric species, the first known examples of well‐characterized macromolecular species with B−B bonds. The oligomeric species were found to comprise up to ten repeat units and are soluble in common organic solvents. Some of the oligomeric species have good air stability and all were characterized by NMR and vibrational spectroscopy and size‐exclusion chromatography techniques.