46055-80-5Relevant articles and documents
Contributions to the Chemistry of Boron, 229. A Deceiving X-ray Single-Crystal Structure Determination: Amino-Hydrogen Exchange in Amino-alkynylboranes and ab initio Investigations of Alkynylboranes, Borirenes, and Boraallenes
Metzler, Nils,Noeth, Heinrich
, p. 711 - 718 (2007/10/03)
Dimeric(dimethylamino)(phenylethynyl)borane (2)2 is formed by the reaction of bis(dimethylamino)(phenylethynyl)borane (1) with 9-BBN-H.An X-ray single-crystal diffraction study revealed a central B2N2 four-membered ring for (2)2 with both alkynyl groups pointing to the same side in a cisoid arrangement.However, solution and solid-state NMR as well as ab initio calculations on model compounds show that the cis arrangement in the crystal chosen for X-ray diffraction is not representative of the bulk material, which consists of both cis and trans isomers.Further investigations of the competition between hydrogen-amino group exchange and hydroboration in the reaction of amino-alkynylboranes with hydroborating agents (9-BBN-H and catB-H) show the exchange to be much faster even in the presence of Wilkinson's catalyst and with cyclic amino-alkynylboranes such as 1,3-dimethyl-2--1,3,2-diazaborolidine (3).Ab initio calculations on alkynylboranes I, borirenes II, and boraallenes III, which are all geometrical isomeres, show alkynylboranes to be the most stable isomers only if strongly ?-donating groups X (X = NH2, F) are attached to the boron atom.In any case, boraallenes are highest in energy. - Keywords: Alkynylboranes; Borirenes; Boraallenes; Calculations, ab initio; Hydroboration
