The products (7)- (9) were characterized by elemental analysis and NMR, IR, and MS spectra. (9) slowly decomposes at 180Β°C. Traces of moisture lead to rapid reaction in accordance with Eq. (b). Compounds ( 7) and ( 8) are also sensitive to hydrolysis and oxidation.
The NMR data of the 3-methylborolan-I-ylamines (7), (8), and (9) [611B: -59.2, -64.0, and -67.8ppm, resp.; 614N : 286,228, and 206 ppm, re~p.][~] confirm the coordination number 3 for the B and N atoms. In spite of the electropositive character of the boron, the borolanyl group withdraws electron density from the N atom through BN n interactions, recognizable by the downfield shift of the 14N-NMR signal and by the 'H-NMR signal of the (CH&Sn group [6'H: -0.16
( 5 ) , -0.26 ( 7 ) , and -0.35ppm (a)].
Because of the low n-electron density on the three boron atoms and the lability of the B-N bonds, ( 9) is a powerful boronating reagentf7].
Tris(3-methylborolan-I -yl)amine (9)
A solution of 1-bromo-3-methylborolane ( 6 ) (5 ml: 6.0g, 37.2 mmol) in toluene (15 ml) is added dropwise at -20Β°C to a stirred solution of tris(trimethylstanny1)amine ( 5 ) (6.25 g, 12.4mmol) in toluene (20ml). The mixture is allowed to warm up slowly and then heated under reflux for 7h. Fractional distillation (10 cm silver-mantle Vigreux column) of the residue remaining after removal of volatiles affords 8.4 g Me3SnBr (93 %; b.p. 28-30Β°C/10-2 torr) and 2.6g (9) (81 %; b.p. 73-74"C/10-2 torr). ( 9) is a water-clear, viscous liquid which is very sensitive toward hydrolysis and oxidation.
Analogous reactions of ( 5 ) with ( 6) in toluene under modified conditions [molar ratios 1 : 2 and 1 : 1, resp.; reaction at 90Β°C (4 h) and room temperature (2 h), resp.] afford the trimethylstannyl(3-methylborolan-I-y1)amines (8) (78 %; b. p. 89-91 "C/10-2 torr) and (7) (75%; b.p. 117--119"C/10~1 torr).