Synthesis, Characterization, and Bromine Substitution of Diamine Complexes of Carboxyborane and Methoxycarbonylborane. Diazabora Rings Containing B-Carboxyl and B-Carboxylato Groups

Abstract

DA·2BH2CN (1) [DA = N,N,N‘,N‘-tetramethylethanediamine (TMEDA, a), N,N,N‘,N‘-tetramethylpropanediamine (TMPDA, b), and N,N,N‘,N‘-tetramethylbutanediamine (TMBDA, c)], (DA·2BH2CNEt)(BF4)2 (2), and DA·2BH2COOH (3) complexes were prepared from Me2S solution of (BH2CN) n (→ 1 → 2 → 3) in fast procedures, differently from those usually applied, in good yields. Dimethyl esters (4) were prepared from 3 with methanol in very fast reactions catalyzed by HBr. 3 and 4 were transformed into DA·BH2COOH (5a,b) and DA·BH2COOMe (6) with DA in THF. Bromination of 3 in aqueous HBr yielded diamine-bis(monobromocarboxyboranes) (7), in vigorous conditions diamine-bis(dibromocarboxyboranes) (9) were produced. N-Bromosuccinimide in methanol transformed 3a,b directly into diamine-bis(bromomethoxycarbonylboranes) (8a,b). BrH·DA·BH(Br)COOH (10a,b) could be prepared from 5a,b with bromine in strongly acidic medium. N-Deprotonated 10a quickly transformed into a five-membered cyclic cation [TMEDA·BHCOOH]+ (cation in 12a) in both water and methanol. Thus, this ion was formed by dissolution of 10a in water, bromination of 5a or destroying one of the borane moieties in 7a by a base. N-Deprotonated 10b in water decomposed with a pH-dependent rate, but in methanol, in the presence of base, it transformed into a six-membered cyclic cation [TMPDA·BHCOOH]+ (cation in 12b). 8a,b could also be transformed into cyclic cations by destroying one of their borane moieties in methanol, (8b in absence of acids only). All cations were prepared as bromide, hexafluorophosphate and tetraphenylborate salts. pK a values of 12a,b (pK a = 5.5−5.6) are 3 units lower than those of amine-carboxyboranes. Zwitterions (18a,b) formed by their deprotonation were prepared. Cyclic cation [TMEDA·B(Br)COOH]+ (cation in 19a) formed on destroying one dibromocarboxyborane of 9a. This cation, quite a strong acid (pK a ≈ 4.2), was prepared as hexafluorophosphate and tetraphenylborate salt. The latter was transformed with aqueous KOH into the corresponding zwitterion (21a).

[B(CO2H)4]− and [B(CNCH3)4]3+: Homoleptic Boron Complexes Containing Carboxy and Methylisocyanide Ligands

“…[26] The pK S3 value for the deprotonation of [B(CO 2 )(CO 2 H) 3 ] 2À is comparable to the value of the [(CF 3 ) 3 …”

“…[26] Its acidity is higher than that of the neutral carboxyboranes that have been described so far, and it is similar in acidity to the [(CH 2 NMe 2 ) 2 BrB(CO 2 H)]…”

Synthesis and examination of amine-cyanocarboxyboranes, the boron analogues of α-cyanocarboxylic acids: X-ray structural study of the first lactam containing a boron atom in the lactam ring

“…One group of reactions was based on earlier examples for the formation of B-CN bond. These experiments included a variety of reactions between A AE BH 2 COOR or A AE BH(Br)COOR (R = H, Me) and either Hg(CN) 2 [23], Me 3 SiCN [24], or AgCN [25]. Considering the ability of trityl cation to abstract hydride from boron [26], the reaction between A AE BH 2-COOMe and Ph 3 CCN [27] was also tested.…”

“…Amine-carboxyboranes (A AE BH 2 COOH), on the basis of the C + -B and CC-BN isoelectronic relationship, are considered as the boron analogues of protonated a-aminoacids [1] and carboxylic acids [2], respectively. Initiated by the similarities to a-aminoacids, aminecarboxyboranes and their precursor amine-cyanoboranes were tested in biological systems and significant antitumor [3] and antiinflammantory [4] activities were found.…”

“…Lately several new derivatives of amine-cyanoboranes and amine-carboxyboranes containing substituents on the boron atom have been prepared in our laboratory, such as amine-bromocyanoboranes (A AE BH(Br)-CN), amine-dibromocyanoboranes (A AE BBr 2 CN), salts of boronium ions having the composition of [AA 0 B(H)-CN] + [18,19], amine-bromocarboxyboranes (A AE BH(Br)-COOH) and their ester derivatives (A AE BH(Br)COOX, X = Me, Et, i-Pr) [2,6,20], amine-dibromocarboxyborane methyesters (A AE BBr 2 COOMe) [20], salts of diaminhydrocarboxyboronium cations [AA 0 B(H)COX] + (X = OH, OMe) [19], cyclic diazaborolidinium and diazaborinanium ions [[C n N 2 B](Y)COX] (n = 2-4; Y = H, Br; X = OH, OMe) [2], as well as amine-dicarboxyboranes and their ester and amide derivatives A AE BH(COX) 2 (X = OH, OMe, NHEt) [21]. Our efforts were driven by the desire to find new or improved biological activities and to understand structure-activity relationships.…”