Chloroboration and allied reactions of unsaturated compounds. Part IV. Boration of di-p-tolylcarbodi-imide

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Abstract
Di-p-tolylcarbodi-imide reacted with a number of boranes [BCl3,BBr3, MeOBCl2, (MeO)2BCl, o-C6H4O2B·SBun, o-C6H4O2B·NEt2, (Et2N)2BCl, PhBCl2, PhB(OMe)2, PhB(NEt2)SBun, Ph2BCl, Ph2B·OMe, Ph2B·SBun, Ph2B·NEt2, and Ph3B] under mild conditions to give high yields of novel borylenebisamidines, boryl-amidines and -guanidines and related compounds, (I), (II), (III), and (IV). These reactions are insertions into the B–X (X = Cl, Br, Ph, OMe, NEt2, or SBun) bond. The synthesis of (III) and (IV) shows that under more forcing conditions it is possible to effect the insertion of more than 1 mol. of a 1 : 2 dipole into the B–X bond. Aminoboration with amine elimination provides a route to the 1,3,5,2-triazaborine (V). By examining the structures of reaction products obtained from the carbodi-imide and mixed boranes, the relative migratory aptitudes (r.m.a.) of the various groups attached originally to boron and ultimately to carbon were established. For example from the reaction Ph2BNEt2+ TolNCNTol → Ph2B·NTol·C(:NTol)·NEt2 the r.m.a. order is NEt2 > Ph. Similar experiments led to the r.m.a. orders (a) NHR > NR2 > SR > Ph > Cl, (b) OR > Ph, and (c) Cl > OR, and it is suggested that these borations are thermodynamically- rather than kinetically-controlled processes. The results are discussed in the context of metallations generally.

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