Iminoborane complex

The finding of preparatively available iminoboranes RB = NR some years ago opened exciting new possibilities not only in B—N chemistry, but also in coordination chemistry. The first examples of iminoborane-transition-metal complexes have now been published. The structurally completely characterized t-BuB = NBu-t adds, like its alkyne analog, to the 03(00)5 fragment as a bridging ligand. When Co2(CO)g and t-BuB = NBu-t are dissolved in pentane at 0°C, warming to RT and evaporation of unreacted iminoborane yields (t-BuBNBu-t)Co2(CO)5 (86%) as a black solid, which can be recrystallized from ether-nitromethane (1 3) ... 

The complexes are formed with 68% (R = t-Bu) and 73% [R = Me2Si(t-Bu)N] yield in warm (85°C) toluene in the course of 90 min. Surprisingly, the B—N distance is extended only a little ( 0.03 A), compared with the free iminoborane. In contrast to this side-on coordinated iminoborane, the zirconium complex (rj -Cp)2ZrCl(H)... 

Some iminoboranes dimerize during reaction with a transition-metal complex to diazadiboretidines. These four-membered rings then act as four-electron donors in different complexes ... 

For reason of symmetry conservation, a thermal concerted [2-1-2]-cycloaddition is forbidden as far as D2h symmetry can be assumed for the activated complex. This is not necessarily the case for the concerted dimerization of iminoboranes, in which the symmetry requirements seem to be essentially lowered. Nevertheless, a two-step mechanism according to Eq. (21) must be taken into account. The assumed intermediate in Eq. (21) contains a sextet boron atom with a linear... 

Azidosilation, of iminoboranes, 31 158, 163 Aziridination, manganese complex applications, 46 402-403... 

Iminoboranes (continued) in transition metal complexes, 31 165-167 X-ray structural studies, 31 135 Iminofluorosulfinamide ions, 19 206-208 Iminofluorosulfonylamide ions, 19 200 Iminolithium complexes, solid-state structures, 37 67-75 dimers, 37 68-70 trimers, 37 68-70... 

Transformations to the cyclotrimeric boiazines and cyclotetrameric tetraza-2,4,6,8,l,3,5,7-tetraboracanes also occur. The rate of dimerization for amino iminoboranes has been shown to be stabilized by bulky substituents (76,79,83). This stabilization through dimerization is essentially a [2 + 2] cycloaddition. There are a number of examples of these compounds forming cycloadducts with other unsaturated polar molecules (78). Iminoboranes can add to electron-deficient carbene complexes of titanium such as (C5H5)2Ti(CH2) [84601-70-7] by [2 + 2] cyclo addition, yielding the metallacycle shown in equation 26 (84). 

The four-membered diazadiboretidine ring system has been formed by several routes including replacement of Sn with B in diazadistannetidines (144), thermolysis of diarylazidoboranes (145), reductive elimination of S from six-membered l,4-dithia-2,6-diaza-3,5-diborinane rings (146), and generally by dimerization of iminoboranes, which are intermediates formed by thermal elimination of chlorotrimethylsilane from aminoboranes as in equation 39 (147,148). Diazadiboretidines act as 4-electron donors forming chromium and tungsten tetracarbonyl complexes (149). 

Upon treatment of indoles with allylic borane, [l,3]hydrogen shift from the nitrogen atom to C-3 proceeds, producing the imine complex 8. Further allylboration of the C=N bond formed occurs with rearrangement through the chair-like six-membered transition state 9 allylic group being added mainly or quantitatively in /ram-fashion relative to the 3-R. Hydrolysis of iminoborane 10 formed leads to the 2-allylated indoline 11. 

Rapid hydrogen releases can be achieved under mild conditions by using transition metal complexes as catalysts. Some noble metal complexes, including Pt, Pd, Rh, Ir, and Ru, were proven to be very effective for promoting hydrogen release from AB. The Rh, Pd, and Ru complexes could catalyze AB to dehydrogenate at room temperature with suppressing the release of volatile cyclotriborazane, borazine, and poly(iminoborane) [107]. The iridium pincer... 

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