Synthesis and reactivity of monoborylacetylene derivatives

The catechol-substituted monoborylacetylenes 1a-d are obtained from the rea ction of bis(diisopropylamino)borylacetylene with catechol derivatives and 2,2'-biphenol. The catalytic trimerization of 1a-d with [(eta (5)-C5H5)Co(C o)(2)] yields isomeric mixtures of the triborylbenzene derivatives 2a,2a', 2b,2b', and 2c,2c'. The reaction of 2a,2a' with mesityllithium provides the hexamesityl-substituted 1,3,5-triborylbenzene 2e. Hydroboration of la with catecholborane affords a mixture of 1,1-bis(1,3,2-benzodioxaborol-2-yl)eth ene (3a) and trans-1,2-bis(1,3,2-benzodioxaboral-2-yl)ethene (4a). Hydrobor ation of la and 3a with one or two mol of HBCl2 and subsequent substitution of the chlorine atoms of the product with catechol leads in each case to t he 1,1,1-trisborylmethane derivative 5a in 83 and 78% yield, respectively w hich forms the tris(THF) adduct 5a(thf)(3). Treatment of 5a with tBuLi yiel ds 1,1, 1-tris[di(tert-butyl)boryl]ethane 6a. [Co-2(CO)(8)] reacts with 1a to give 3-(1,3,2-benzodioxaborol-2-yl)-1,2-bis(tricar-bonylcobalta)tetrahed rane (9a). The new compounds have been characterized by NMR spectroscopy an d mass spectrometry as well as by X-ray structure analyses for 1a, 3a, 5a, 5a(thf)(3), and 9a.