Protolysis of Tri‐ tert ‐butylazadiboriridine: Formation of a B‐H‐B Bridge in Unusual Coordination

The BB bond of tri‐ tert ‐butylazadiboriridine [NRBRBR] (R = t Bu; 1 ) is oxidized by MeOH to give the (hydroboryl)(methoxyboryl)amine HBRNR‐BR(OMe) ( 2a ). μ‐2,3‐Hydroazoniadiborata‐1‐cyclopropenes [NRBR(X)μHBR] ( 3a, 3c‐e ) are formed by the action of the acids HX upon 1 . A similar hydrogen bridge as in 3a‐e is formed during the hydroboration of 1 by catecholborane, yielding 3f . A B atom is identified in the products 3a‐f to be planarly coordinated by four atoms, two of which are forming a BHB three‐center bond with that B atom. This is a novel bonding situation in boron chemistry. The structures of the products are deduced from 1 H‐, 11 B‐, and 13 C‐NMR spectra and are confirmed by X‐ray structural analyses of 2a, 3a , and 3c.