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

Abstract

Several transamination reactions of B2(NMe2)4 (1a) with secondary amines have led to mixed tetraaminodiborane(4) compounds B2(NMe2)4 ‐ n(NR2)n (2–4), and B2(NC5H10)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 R2N(Me2N)B‐B(NMe2)NR2 are more readily accessible from LiNR2 and B2(NMe2)2Cl2. Similarly, amination of B2(NMe2)2Cl2 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–CH2–CH2–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 B2(NMe2)2Br2 with 9 which gives exclusively the corresponding 1,4,2,3‐diazadiborinane 11. Diborane(4) dihalides B2(NMe2)2X2 (X = Cl, Br) react only in a 1:1 ratio with tmp‐B=N‐CMe3 (13) leading to 14a, b. However, both a 1:1 and a 1:2 methoxyboration of 13 has been observed with B2(OMe)4 with formation of 15 and 16.

Synthesis and structures of monocyclic 1,4-diaza-2,3-diborine species

“…NICS(0) zz and NICS(1) zz values are negative sign of out-of-plane zz-component of the magnetic shielding tensor, suggesting that there may be an aromaticity index [21,22]. B NMR spectra of 3ad, 3ae, 3bc and 8a exhibit a characteristic broad singlet at 47, 48, 32 and 56 ppm, respectively, which is consistent with a symmetrically substituted aminodiborane [26]. For 3bc, the 11 B NMR signal of the equivalent boron atoms is shifted upfield, as expected for symmetrically substituted tetraaminodiborane compounds, because the boron atoms are more shielded by the dimethylamino groups (δ=32 ppm).…”

Recent developments in the chemistry of 1,3,2-diazaborolines-(2,3-dihydro-1H-1,3,2-diazaboroles)

“…The preparation of diboranes (4) by alkali-metal reduction of halogenoboranes XBR 2 (X = Cl, Br; R = Me 2 N, Aryl) is meanwhile state of the art [51]. Their further reduction to dinuclear mono-and dianions was recently reported [52,53] (Scheme 51).…”

Synthesis and Structure of the First [1]Boratitanocenophanes

“…After stirring for 1 h, all volatiles were removed in lecular sieves. (Me 3 Si) 2 NBCl 2 , [15] NaC 5 H 5 , [16] Ti(NMe 2 ) 4 , [17] high vacuum, and the remaining solid was suspended in 20 mL of [TiCl 3 (thf) 3 ], [18] and (C 4 H 8 N) 2 BCl [19] …”