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 (original) (raw)
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Journal of Organometallic Chemistry, 2004
The first representatives of chiral boron atom-containing amine-cyanomethoxycarbonyl boranes (A AE BH(CN)COOMe) have been synthesized either from the corresponding amine-bromocyanomethoxycarbonylborane complexes with [Bu 4 N]CN or from Me 3 N AE BH(CN)COOMe and an amine in a base-exchange reaction. Acid hydrolyses of methyl esters generated the free acids (A AE BH(CN)COOH), which are isoelectronic to the a-cyano carboxylic acids. Their pK a values and hydrolysis half-lives in acidic medium (that is rate of proton reduction) have been determined. Similarly to the alpha cyano carboxylic acids, the cyano group attached to the boron (in alpha position to the COOH group) increased the acid strength of carboxy boranes with 2.0-2.5 orders of magnitude. Independently from the type of the amine, pK a values of the amine-cyanocarboxyboranes (6.34-5.82) decrease consistently with the increase of pK b values of the amines. Hydrolytic decomposition rate of the alkylamine complexes increases with increasing pK b values of the amines while the opposite was found for pyridine base complexes. When considering both types of the amines, hydrolysis half-lives of the complexes range over several orders of magnitude from 0.005 to 400 h. Based on these observations protonation of the amine nitrogen atom appears to be the rate determining step in the hydrolysis process. With loss of methanol, 2-NH 2 -py AE BH(CN)COOMe transformed into a five membered lactam derivative. X-ray diffraction revealed that the pyridine ring is coplanar with the five membered lactam ring. In the crystal two molecules are connected in a head to tail arrangement by strong intermolecular H-bonds between N(2)-H and the carbonyl oxygen (O1) with a donor and acceptor distance of 2.867(3) Å . Three new cyanomethoxycarbonylborates having the composition of K[BH n (CN) 3Àn COOMe] (n = 1, 2) and K[B(OH)(CN) 2 -COOMe] have also been synthesized and their properties examined.
Inorganic Chemistry, 2001
Amine-bis(N-ethylcarbamoyl)boranes [A‚BH(CONHEt) 2 , 3; A) trimethylamine (Me 3 N, a), quinuclidine (Q, b), pyridine (py, f), 4-picoline (pic, g)] have been prepared after deprotonation of [amine-bis(C-hydroxy-Nethylimidate)hydroboron(2+)] cations (2), which were formed by the hydrolysis of [amine-bis(ethylnitrilium)hydroboron(2+)]tetrafluoroborates (1). Numerous representatives of 3 [A) diethylamine (Et 2 NH, c), piperidine (pip, d), pyrrolidine (pyrr, e), 4-aminopyridine (4-NH 2-py, h), 4-(dimethylamino)pyridine (DMAP, i), imidazole (Him, j), 1-methylimidazole (Mim, k)] have been prepared by base exchange reactions from 3a. 3a-e are extremely stable in aqueous media, either acidic or alkaline, probably because of the considerable steric hindrance of possible reaction centers. However, they were transformed into amine-dicarboxyboranes [A‚BH(COOH) 2 , 4a-e] in acidic medium under vigorous conditions (100-130°C). This transformation was accompanied by significant decomposition, probably owing to the protonation on the N atom, resulting in the rupture of the B-N bond. As an exception, 4b, where N atom in a rigid bicycle is not prone to attacks, could be isolated in very good yield. On the other hand, amine-bis(N-ethylcarbamoyl)boranes containing amines with sp 2-hybridized N atoms (3f-k) undergo complete decomposition under similar conditions probably because of the increased hydridic character of the hydrogen adjacent to boron. Base exchange reactions starting from 4b resulted in the ammonium salts of 4c-e, h, i of composition [A‚BH(COOH)(COO-)][AH + ], which in turn could be transformed into the diacids 4, except 4h, by protonation. As salt formation indicates, the 4 compounds are stronger acids as univalent acids than the corresponding A‚BH 2 (COOH) complexes. 4a-e, i were readily esterified into amine-bis(methoxycarbonyl)boranes (5a-e, i) in methanol, employing a catalytic amount of HBr. 5a-e, i are stable in alkaline medium but are readily hydrolyzed in acidic medium. Hydrolysis of [amine-bis(C-methoxy-N-ethylimidate)hydroboron(2+)] cations did not give the corresponding bisesters 5 in alkaline, neutral, or acidic medium.
Inorganic Chemistry, 1999
Numerous amine-dicyanohydroboranes [A‚BH(CN) 2 , 1, A) quinuclidine (Q, c), trimethylamine (Me 3 N, d), 4-picoline (Pic, e), 4-(dimethylamino)pyridine (DMAP, f), N,N,N′,N′-tetramethylethylenediamine (TMEDA, j), 1,4-diazabicyclo[2.2.2]octane (DABCO, k)] have been prepared by base exchange reactions from 4-cyanopyridinedicyanohydroborane (4-CN-py‚BH(CN) 2 , 1a). In analogous experiments with secondary amines [piperidine (g), diethylamine (h), and morpholine (i)] 1a underwent aminodecyanation also, probably via S N Ar mechanism, which demonstrates the strong electron-withdrawing effect of the >N‚BHX 2 moiety toward the substituents on the nitrogen. Amine-dicyanohydroboranes have been transformed into [amine-bis(C-hydroxy-N-ethylimidate)hydroboron(2+)] (3), [amine-N-ethylcarbamoyl(C-hydroxy-N-ethylimido)hydroboron(1+)] (4), [amine-bis(C-methoxy-N-ethylimidate)hydroboron(2+)] (5), [amine-bis(amidinium)hydroboron(2+)] (6), and [amine-bis(triethylamidinium)hydroboron(2+)] (7) cations, precursors of amine-dicarboxyboranes and their derivatives. These transformations were carried out in two steps. First, the otherwise nonreactive cyano groups were activated by ethylation employing Et 3 OBF 4 , yielding [amine-bis(ethylnitrilium)hydroboron(2+)] tetrafluoroborates (2), then 3-7 were obtained by nucleophilic addition to 2. The pK a values corresponding to the protonation of the N-ethylamide group were found to be extremely high (3.1-3.3), which demonstrates the strong electron-donating effect of >N‚BHX 2 moiety toward the substituents on the boron.
Inorganica Chimica Acta, 1995
Symmetrical bis(amine)(methoxycarbonyl)hydroboron(+ 1) cations have been prepared by treatment of trimethylaminebromo(methoxycarbonyl)borane [Me,N-BH(Br)COOMe] with an excess of tertiary amines (tetramethylethylenediamine, TMEDA, quinuclidine, Q), as well as pyridine bases (pyridine, Py; 4-methylpyridine, 4-Pit; 4_dimethylaminopyridine, DMAP) at higher temperature. Asymmetrical bis(amine)(methoxycarbonyl)hydroboron(+ 1) cations, which contain a chiral boron atom, have been synthesized, in good yields, in the reaction of 4-Pic*BH,COOMe and DMAP*BH,COOMe with amine perbromides (L-Br2, L=Q, Py, 4-Pit, DMAP) performed in C&Cl2 at room temperature. Besides these novel cationic carboxyboron compounds several new cationic cyanoboron complexes with an [LL'BH(CN)]+ composition have been prepared by utilizing the efficient method employing amine-perbromides (L.Br,; L=Py, 4-Pit, DMAP) and amine-cyanoboranes (L' .BH2CN, L' = 4-Pit, DMAP). The bis(amine)boronium cations have been prepared and characterized by IR, 'H and "B NMR spectra as PF, salts. Investigations of the water-soluble bis(amine)(methoxycarbonyl)hydroboron(+ 1) bromides, some of which could be prepared, showed that the hydrolytic stability of the ester group highly depends on the character of the amine: the complexes formed with tertiary amines are much more stable. This phenomenon is similar to that observed for the amine-(methoxycarbonyl)boranes (L-BH,COOMe, L= tertiary amine, pyridine base).
Inorganica Chimica Acta, 2003
Substituted-borane adducts of amines and a -amino acids, pyridine-N -ethylcarbamoylborane (1), (carboxy or cyano)-dihydro[{1-(R)-2-amino-2-oxoethyl] amino}boron] (2a Á/g) (R0/CH 2 Ph, CH 2 PhOH, CH 3 , CH(C 2 H 6 ) and N -[(trimethylamineboryl)-carbonyl]-{(3, 4-dihydroxyphenyl)-L-alanine}-methylester (3) are synthesized in 63 Á/93% yields. All compounds were characterized by elemental analysis, 1 H, 11 B and 13 C NMR and IR spectroscopy. Additionally, the structure of compound 1 was determined by single crystal X-ray diffraction. #
Cations derived from BH2+. Unsymmetrical bis-amine substitution on boron
Journal of the American Chemical Society, 1969
Salts of boron cations, with two different tertiary amines coordinated to a BH2+ group, have been synthesized by displacement of iodide from adducts of monoiodoborane with trimethylamine, triethylamine, or pyridine. Pyridines substituted with a variety of functional groups, quinoline, N,N-dimethylanilhe, and triethylamine were used as the second amine. The success of the preparation of these cations was found to depend o n the basicity of the displacing amines and favorable steric factors. Carbonyl and nitrile substituents, which are normally reduced by B-H bonds, did not interfere with the synthesis. The cations could be converted to symmetrical derivatives by transamination. The compounds were stable a t room temperature to Ag+, Hgz+, Cue, Cr207*-, and HzOL, as well as t o acid or base. They decomposed slowly in hot HCl, water, or NaOH.