PROTOLYSIS OF TRI-TERT-BUTYLAZADIBORIRIDINE - FORMATION OF A B-H-B BRIDGE IN UNUSUAL COORDINATION

The B-B bond of tri-tert-butylazadiboriridine [-NR-BR-BR-] (R = tBu; 1 ) is oxidized by MeOH to give the (hydroboryl) (methoxyboryl)amine H-B R=NR-BR(OMe) (2a). mu-2,3-Hydroazoniadiborata-1-cyclopropenes [=NR-BR( X)-mu H-BR=] (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 hydrobora tion of 1 by catecholborane, yielding 3f. A B atom is identified in th e 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 H-1-, B-11-, and C-13-NMR spectra and are confirmed b y X-ray structural analyses of 2a, 3a, and 3c.