In a series of donor-acceptor adducts of amines to triorganylboroxines (Tables 1, 2) it has been shown by 'H and "B NMR spectroscopy that in solution the amine undergoes a temperature dependent fluctuation between the boron atoms of the boroxine ring. In the solid state, as determined by X-ray structural analysis of two selected 3 : 2 and 1 : 2 adducts (3 and 6) (boron-nitrogen ratios of 1 : 1 and 3 : 1, respectively), only one boron atom of each boroxine ring is involved in adduct formation.
Die Struktur von Amin-Addukten von TriorganylboroxinenIn einer Reihe von Donor-Acceptor-Addukten von Aminen mit Triorganylboroxinen (Tabb. 1, 2) wird gezeigt, da8 in Losung die Aminmolekule zwischen den drei Boratomen des Boroxin-Rings fluktuieren. Im festen Zustand, wie es aus den Rontgenstrukturanalysen von zwei ausgewahlten 3 : 2-und 1 : I-Addukten (3 und 6) (mit Bor-Stickstoff-Verhaltnissen von 1 : 1 bzw. 3 : 1) hervorgeht, ist nur ein Bor-Atom des Boroxin-Rings an der Adduktbildung beteiligt.Simple and cyclic esters of monoorganylboronic acids act as weak Lewis acids and usually do not form donor-acceptor complexes with amines. We have previously shown that the boron atoms in 1 act as strong acceptors for amines and that adducts with up to four amines per molecule of 1, i.e., a boron to nitrogen ratio of 1 : 1, can be formed').This complex forming ability is similar to that of the triorganylboroxines which also readily form adducts having the general formula (RBO), . NR; (2). In all but one of these the amine to boroxine ratio is 1 : 3 and may formally be regarded as being uniformly bonded to the three boron atoms of the boroxine ring. The only exception is 0 Verlag
The mechanism for the stereoselective formation of the product is discussed.We have previously reported the synthesis of 1,2,3selenadiazoles (I).2 Light-and heat-induced decom-
The hydroboration of H11C6N=C=NC6H11(A) with (9H-9-BBN)2 (C2) gives H11C6N= C(H)N(C6H11)BC8H14 (1), which reacts with 9H-9-BBN to form the six-membered heterocycle mixed dimer (2). Compound 2 crystallizes in the monoclinic space group C 2/c, a = 27.776(3). b = 17.140(2), c = 12.302(2) Å, β = 113.31° (at 120 K). - On heating. 2 is transformed by intramolecular hydroboration into H2C[N(C6H11)B(C8H14)]2 (3a). - 1 reacts with Et2O-BF3 to give 9F-9-BBN (4) and (5). - The total hydroboration of H5C6N=C=NC6H5 (B) with C2 affords H2C[N(C6H5)B(C8H14)]2 (3b).
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