Pseudohalides. Part IV. Infrared spectra and thermochemistry of the complexes PhBX2,L (X = Cl, Br, NCO, or NCS; L = C5H5N or EtOAc), and relative acceptor strengths of halogeno- and pseudohalogenoboranes; with notes on the chemistry of four-co-ordinate isocyanato- and isothiocyanato-boranes

Publisher Website
Google Scholar
Abstract
Eight complexes PhBX2,L (X = Cl, Br, NCO, or NCS; L = C5H5N or EtOAc) have been prepared and characterised. Their i.r. spectra have been examined and assignments are proposed. The most significant feature is probably the progressive decrease in ν(CO) in the series PhBX2,EtOAc from 1639 (X = NCO), to 1597 (X = NCS), 1582 (X = Cl), and 1563 cm.–1(X = Br) compared with 1714 cm.–1 in free EtOAC. These changes reflect the inverse order of acceptor strengths (X = Br > Cl > NCS > NCO) in PhBX2. The same result is found calorimetrically, using pyridine as the ligand; but for the EtOAc–PhBX2 system there are complicating side reactions (the 1 : 1 complexes dissolve exothermically in excess ligand). The condensed-phase heats of the reaction (where l = liquid and c = crystal): PhBX2(l)+ py(l)= PhBX2,py(c) are –39·1, –33·2, –28·7, and –26·2 kcal. mole–1 for X = Br, Cl, NCS, and NCO, respectively. The compounds B(NCO)3,py, B(NCS)3,py, o-C6H4O2BNCO,py, Ph2BNCO,py, and PhB(Cl)NCO,py are reported. B(NCX)3,py (X = O or S), was obtained from BY3,py (Y = halogen) and AgNCX (probably by a predissociation mechanism); the other complexes were prepared directly from their components. Reactions with alcohols and amines are described. Four-co-ordinate pseudohalogenoboranes generally behave like their three-co-ordinate progenitors. An exception is found in the B(NCO)3,py–RR1NH system which leads to B(NH·CO·NRR1)3.

This publication has 0 references indexed in Scilit: