Tetra‐ tert ‐butyltetraborane(6) B 4 H 2 t Bu 4 : A Derivative in the Series B n H n +2

The reaction of RBBr 2 and Na/K alloy or the two‐step reaction of B 4 R 4 and Na/K alloy with subsequent action of HCl results in the tetraborane B 4 H 2 R 4 (R = t Bu). A tetrahedral B 4 structure 1 with two hydrogen‐bridged opposite edges ( D 2d symmetry) is deduced from NMR data for B 4 H 2 R 4 as well as from ab initio calculations for the parent molecule B 4 H 6 and for B 4 H 2 Me 4 . Upon reaction with lithium in tetrahydropyran (L), a bridging H atom on B 4 H 2 R 4 can be replaced by the group LiL 2 . (L 2 Li)B 4 HR 4 was characterized by a crystal structure analysis.