Contributions to the chemistry of boron. Part 242. Rearrangement of bis(dimethylamino)bis(1-indenyl)diborane(4) into bis(dimethylamino)bis(3-indenyl)diborane(4)

Indenyllithium reacts with dichlorobis(dimethylamino)diborane(4) with formation of bis(dimethylamino)bis(1-indenyl)-diborane(4) which rearranges on heating to the isomer bis(dimethylamino)bis(3-indenyl)diborane(4). The mixed isomer bis(dimethylamino)(1-indenyl)(3-indenyl)diborane(4) was obtained from indenyllithium and chlorobis(dimethylamino)(3-indenyl)diborane(4). Crystal data of 1,2-bis(dimethylamino)-1,2-bis(1-indenyl)diborane(4) (I): monoclinic, space group P21/c, a 15.8977(3), b 7.5756(1), c 16.8297(3) .ANG., b 93.323(1) Deg, Z = 4, rc = 1.116 g/cm3, m(MoKa) = 0.064 mm-1, F(000) = 728, 2781 obsd. reflections with I > 4s(I), R = 0.0789, wR2 = 0.1812; 1,2-bis(dimethylamino)-1-(1-indenyl)-2-(3-indenyl)diborane(4) (II): triclinic, space group P.hivin.1, a 8.8466(1), b 10.3594(2), c 11.1737(3) .ANG., a 77.403(1), b 85.428(1), g 83.222(1) Deg, Z = 4, rc = 1.140 g/cm3, m(MoKa) = 0.065 mm-1, F(000) = 364, 2640 obsd. reflections with I > 4s(I), R = 0.0474, wR2 = 0.1141. The main structural differences between the 2 isomers I and II are a slightly shorter B-B bond in II, as well as a stronger twist about the B-B bond (89,9 Deg vs. 67.4 Deg) and, as expected, a shorter B-C bond. There is, however, no significant B-C p bonding. [on SciFinder (R)]