No abstract

In order to establish the suggestion arising from the assignment of the cluster 11B and 1H NMR shielding behavior, namely, that the title compound (I) is not a closo species, a single‐crystal X‐ray diffraction analysis is carried out (space group P21/c, Z=4).

Reactions between arachno-4-SB8Hl2 (1) and Lewis bases L in benzene or without solvent generate a series of the corresponding exo-6-L-arachno-4-SBgHlo (2) compounds [L = SMe2 (2a), PPh3 (2b), MeCN (2c), NMe3 (2d), pyridine (py) (2e), urotropine (uro) (201, and a bidentate-ligand adduct exo,exo'-6,6'-(uro)-(arachno-4-SBgH10)2 (2g) has also been isolated. Compound 2d has also been prepared by a ligand displacement reaction between 2a and trimethylamine, and similar adducts with L = MeNC and quinoline (quin) (2h, 2i) were isolated as side products from the reactions between nido-6-SB9H11 (3) and corresponding Lewis bases. All these compounds are characterized by mass spectrometry and llB and 'H NMR spectroscopy. Single-crystal X-ray diffraction studies have been canied out on three representatives of the series, viz. those with L = uro (20, l/2 uro (Zg), and MeNC (2h). Crystal data for 2f (at 200 K): mol wt 268.9; monoclinic; space group C2/c; Z = 8; a = 2064.16(9), b = 680.85(5), c = 2061.61(12) pm; j 3 = 104.467(5)"; R = 0.0647; R, = 0.0743. Crystal data for 2g (at 200 K): mol wt 397.6; monoclinic; space group P211c; Z = 4; a = 1228.24(8), b = 1296.79(8), c = 1452.62(10) pm; , 8 = 110.394(4)"; R = 0.046; R, = 0.0543. Crystal data for 2h (at 200 K): mol wt 169.8; monoclinic; space group P21/m; Z = 2; a = 557.93(8), b = 909.36(9), c = 987.16(11) pm; R = 0.0377; R, = 0.0436.

The closo-1 ,2-C2BloH12 dicarbaborane (1) undergoes regiospecific cluster degradation reactions via the [nido-7,9-C2BIOH13]-anion (2) in the presence of Lewis bases L. When L = NMe3, the reaction is found to proceed via carbon-vertex loss to isolate the ten-vertex intermediate endo-9-Me-8-(NMe3)-arachno-6-CBsHlz (3). Further boron-vertex loss occurs to yield a series of arachno nine-vertex compounds exo-6-L-4-CB8H12 (4) [where L = NMe3,4a; pyridine (py), 4b; urotropine (uro), 4c; l / 2 uro, 4; and SMe2,4e]. Ligand-exchange reactions between 4e and stronger Lewis bases, such as py, uro, quinoline (quin), MeCN, PPh3, and MeNC, afforded compounds 4b-d and further species of type 4 (where L = quin, 4fi MeCN, 4g; PPh3, 4b; and MeNC 4i). These all have clusters that are isostructural with the unsubstituted parent dicarbaborane arachno-4,6-CzB7Hl3, as documented by X-ray diffraction analysis on 4c. Crystal data for 4c: mol wt 251; triclinic; space group Pi; 2 = 4; a = 581.78 (4), b = 1079.87(6), c = 1181.40(7) pm; a = 105.331(4), j. 3 = 94.854(4), y = 92.797(4)'; U = 0.71 127(8) nm3; R = 0.0423 and R, = 0.0503 for 2056 reflections with Fo > 3a(F0). Compound 3 can be oxidized to 9-Me-8-(NMe,)-nido-6-CBgHlo (5b) by acetone, and a similar anionicspecies, [9-Me-8-(HO)-nido-6-CB9Hl0]-[PPh4]+ (Sb), was obtained directly from anion 2 by treatment with acetone. All compounds have been characterized by 1lB and 1H N M R spectroscopy, and the unambiguous assignment of the IlB and 'H resonances permits comparisons with the shielding patterns of the structurally related parent analogs such as neutral arachno-4,6-C2B7H13, the anion [arachno-6-CB9H14]-, and the anion [nido-6-CB9H12]-.

Das Heteroboran (I) und Benzylbromid (II) reagieren in Diäthyläther in Gegenwart von Karliumhydroxid zur gesuchten Verbindung (III).