Borazol

Diboran reduziert Nitrile schneller als Epoxide und Carbonsaure-ester, aber langsa-mer als Ketone, Olefine und Carbonsauren, so dab selektive Reduktionen moglich sind (s. S. 48). Da aus Nitrilen mit Diboran die stabilen N,N,N-Trialky 1-borazole gebildet... 

Analogon des entsprechenden Borazols (ClBNMe)3, jedoch nicht wie dieses niedermolekular, sondern hochmolekular, da das Al-Atom in allge-meinen Koordinationszahlen von KZ 4 anstrebt. Fur das Produkt wurde die Struktur XVII vorgeschlagen (116). 

Die Produkte der Thermolyse von (CH3)2BN3 Py bei 210—220 °C wur-den gaschromatographisch untersucht (11) Neben dreiBig anderen Pro-dukten entsteht als Hauptprodukt in 21proz. Ausbeute Hexamethyl-borazol. 

When the same microcalorimetric methods are applied to hexaalkylborazole complexes, [(R3B3N3R3)Cr(CO)3] (R = Me, Et), it is possible to show84) that, for both complexes, the b.e.c of the (Cr-borazole) bond should lie in the range 70—140 kJ mol-1, with the true value probably in the range (105 12) kJ mol-1. 

A qualitatively similar dependence of ADh on boron orbital hybridization is noted in boron hydrides (104). -1bh = 81 cps for BHr where boron is tetrahedral while ABH = 136 cps for borazole where boron presumably is sp2. A ijh for BH3 adducts with ethers, amines, and phosphines range between 90 and 103 cps and for these compounds boron quadrupole coupling constants have been interpreted (22) in terms of a boron hybridization intermediate between sp2 and sp2. However, the simple dependence of... 

Figure 7 The structure of endohedral fullerene clusters with benzene and borazole molecules encapsulated into Cs4 ( >6a).

Calculations of the borazole endocluster B3N3H6 Cs4 (Ihi,) [34] give a similar qualitative pattern with some quantitative differences. Upon encapsulation, the B-N bond is 0.01 A more shortened than the C-C bond. 

The contraction of borazole leads to an enhancement of the polarity of all bonds (endocyclic B-N and exocyclic B-H and N-H) (Table 13), in contrast to the benzene molecule, whose contraction is accompanied by an increase in the covalent component of the C-H bonds. The charge transfer between the C84 cage and the B3N3H6 and C6H6 guests is small. 

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