Chemistry of Diborane(4) Derivatives: Mixed Tetraaminodiboranes(4) and Additions of Diborane(4) Derivatives to an Amino‐imino‐borane

Several transamination reactions of B 2 (NMe 2 ) 4 ( 1a ) with secondary amines have led to mixed tetraaminodiborane(4) compounds B 2 (NMe 2 ) 4 ‐ n (NR 2 ) n ( 2 – 4 ), and B 2 (NC 5 H 10 ) 4 ( 1d ) has been characterized by an X‐ray structure analysis which reveals the presence of a rather long B–B bond (1.75 Å). However, tetraaminodiboranes(4) of type R 2 N(Me 2 N)B‐B(NMe 2 )NR 2 are more readily accessible from LiNR 2 and B 2 (NMe 2 ) 2 Cl 2 . Similarly, amination of B 2 (NMe 2 ) 2 Cl 2 with N,N '‐dimethylethylenediamine ( 7 ) yields B ‐[bis(dimethyl‐amino)boryl]‐ N,N' ‐dimethyl‐1,3,2‐diazaborolidine ( 8 ), while reactions with Li(Me)N–CH 2 –CH 2 –N(Me)Li ( 9 ) lead also to 2,3‐bis(dimethylamino)‐1,4‐dimethyl‐1,4,2,3‐diazadiborinane ( 10 ) as the kinetically controlled product. This is further substantiated by the reaction of the B 2 (NMe 2 ) 2 Br 2 with 9 which gives exclusively the corresponding 1,4,2,3‐diazadiborinane 11 . Diborane(4) dihalides B 2 (NMe 2 ) 2 X 2 (X = Cl, Br) react only in a 1:1 ratio with tmp‐B=N‐CMe 3 ( 13 ) leading to 14a , b . However, both a 1:1 and a 1:2 methoxyboration of 13 has been observed with B 2 (OMe) 4 with formation of 15 and 16 .