Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B-B Bond

Deprotonation of the doubly arylene-bridged diborane(6) derivative 1H₂ with (Me₃ Si)₃ CLi or (Me₃ Si)₂ NK gives the B-B σ-bonded species M[1H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4'-di-tert-butyl-2,2'-biphenylylene). With nBuLi as the base, the yield of Li[1H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[2H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[2H] are linked by a μ-H bridge. In the closely related molecule Li[3H], the corresponding μ-H atom can be abstracted with (Me₃ Si)₃ CLi to afford the B-B-bonded conjugated base Li₂ [3] (THF, 150 °C; 15 %). Li[1H] and Li[2H] were characterized by NMR spectroscopy and X-ray crystallography.