Diazaboroles

H-1,3,2- Diazaborole, 1,2-dihydro-reactions, 1, 641 synthesis, 1, 639, 640 transition metal complexes, 1, 641 Diazadiborine, tetrahydro-semi-empirical calculations, 1, 632 Diaza[2.2.2]cryptand synthesis, 7, 750 Diazacryptands bispyridine... 

A series of 1,3,2-diazaboroles in a thermal substitution reaction with [Cr(CO)3(AN)3] forms the j -coordinated complexes 59 (R = R = Me, Et, /-Pr R = Me, R = Et) (90IC4421). The corresponding dimeric ligand in this reaction yields complex 60 where only one heteroring is j -coordinated. 

Neutral 2,3-dihydro-lH-l,3)2-diazaboroles are isoelectronic with the cyclopenta-dienyl anion and, therefore, prefer to react with neutral transition-metal fragments having 12 electrons ... 

The reactivity of nucleophilic carbenes toward 2-bromo-2,3-dihydro-lff-l,3,2-diazaborole has also been described (37). The reaction of... 

Many X-ray data are given for these bicyclic 5-6 systems, as a method for structure confirmation or elucidation of unexpected reaction products. Analysis of compound 25 (Scheme 5) revealed a planar molecule, in which the B-N distances (1.420 and 1.429 A) indicate a multiple bond character, since in diazaboroles they range from 1.395 to 1.450 A... 

A somewhat different synthetic strategy was put into practice a saturated ring was prepared and the unsaturation was achieved by means of catalytic dehydrogenation. In this way some monocyclic l,2-dihydro-3H-l,3,2-diazaboroles (71) were prepared (Scheme 6) (74MI12100, 81MI12100). 

Figure 2 Effect of substituents on 11B NMR chemical shifts of oxaza- and diazaboroles.

The presence of different elements attached to boron atom does not significantly alter the chemical shifts. Diazaboroles 9a-e substituted with carbon (8 29.5), silicon (8 29.9), germanium (8 30.5), tin (8 32.8), and lead (8 39.6) <2003AOM525>, as well as dioxaborolanes lOa-g substituted with sulfur (8 34.3), selenium (8 35.3), silicon... 

The reaction of diphenylketene with 1,3,2-diazaboroles 234 in hexane at — 20 °C leads to the formation of 1,3,2-oxazaborolidines 238 in 64-70% yield. The reaction proceeds via the coordination of the ketene oxygen to boron 236 followed by a [2+3] cycloaddition yielding the bicyclic intermediate 237. Fission of B-N bond leads to the product formation as yellow to colorless crystals (Scheme 40) <20000M5791>. 

The reactivity of nucleophilic carbenes with 2-bromo-2,3-dihydro-l//-l,3,2-diazaborole has also been described. Reaction of a benzene solution of (1) (R = Me, i-Pr R = H) I-----------------------1... 

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