Borylated Tetrazoles from Cycloaddition of Azide Anions to Nitrilium

Article pubs.acs.org/Organometallics

Borylated Tetrazoles from Cycloaddition of Azide Anions to Nitrilium Derivatives of closo-Decaborate Clusters Aleksey L. Mindich,† Nadezhda A. Bokach,*,† Maxim L. Kuznetsov,‡ Galina L. Starova,† Andrey P. Zhdanov,§ Konstantin Yu. Zhizhin,§ Serguei A. Miltsov,† Nikolay T. Kuznetsov,§ and Vadim Yu. Kukushkin*,†,⊥ †

Department of Chemistry, Saint Petersburg State University, Universitetsky Pr. 26, 198504 Stary Petergof, Russian Federation Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade Técnica de Lisboa, Avenida Rovisco Pais, 1049-001 Lisbon, Portugal § N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Pr. 31, 119991 Moscow, Russian Federation ⊥ Institute of Macromolecular Compounds, Russian Academy of Sciences, V.O. Bolshoi Pr. 31, 199004 Saint Petersburg, Russian Federation

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‡

S Supporting Information *

ABSTRACT: Interaction of the closo-decaborate clusters [Bun4N][B10H9(NCR)] (R = Me 1a, Et 1b, But 1c, Ph 1d) with the azide [Ph3PNPPh3]N3 proceeds immediately upon mixing the reagents in an MeCN solution at RT, giving the borylated 1,5-disubstituted tetrazoles [B10H9(N4CR)]2− in essentially quantitative yield. On a synthetic scale, sodium azide, NaN3, reacts similarly with the nitrile functionality of 1a−d in an acetonitrile suspension under mild conditions (RT, 15 h) to afford selectively the borylated tetrazoles [Bun4N]2[B10H9(N4CR)] (2a−d; 88−96% isolated yields) and the water-soluble Na2[B10H9(N4CR)] species (3a−d; ca. 95% isolated yield) after the metathetical reaction with NaBPh4 in MeOH/H2O. The reaction with N3− represents the first example of the propargyl-allenyl anion type dipole cycloaddition (CA) to the nitrilium derivatives of any boron clusters. Reactions of 1a−d with alkyl or aryl azides (p-Me-C6H4-COCH2N3, p-NO2-C6H4-CH2N3, PhN3) do not proceed even under harsh conditions (2 d, dry EtCN, 100 °C, under Ar). However, corresponding 1,4,5-trisubstituted tetrazoles 4a−d, 5, and 6 and 1,3,5-isomers 4′a−d, 5′, and 6′ were obtained by alkylation of 2a−d. The isomers were separated by column chromatography and identified by 2D NOESY NMR and X-ray crystallography (for 5 and 6′). Compounds 2a−d, 3a−d, 4a,b, 4′a−d, 5, 6, 5′, and 6′ were characterized by ICP-MS-based B analysis, high-resolution ESI-MS, molar conductivity, IR, and 1H, 13C{1H}, and 11B{1H} NMR spectroscopies. The structures of 2c, 5, and 6′ were elucidated by single-crystal X-ray diffraction. Theoretical calculations at the DFT level (B3LYP and M06-2X functionals) allowed the establishment of the reaction mechanism, which is stepwise in the case of the azide-ion CA and concerted asynchronous (by 30−43%) for the hypothetical CA of RN3. The higher reactivity of N3− toward the borylated nitriles in comparison with organic azides RN3 (by 10.8−18.7 kcal/mol in terms of ΔGs⧧ values calculated at M06-2X) is mostly accounted for by the solvent effects, and these reactions are controlled by kinetic rather than thermodynamic factors.

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INTRODUCTION Although one of the most interesting substrates with high boron atom content applicable for modifications are nitrilium derivatives of boron clusters, their reactivity still remains scarcely investigated. However, the data for various borylated nitrilium species gradually emerging in the literature uncover a high reactivity of the CN group that is subject to facile additions of H2O,1−3 ROH,4−6 amines,4,5,7 and azomethine ylides,8 thus providing an easy route for the functionalization. Recently, performing studies (for a review see ref 9; for recent works see refs 10−14) on the activation of the CN moiety toward cycloaddition (CA) we suggested a novel approach for functionalization of boron clusters, viz., CA of © 2013 American Chemical Society

nitrones (as allyl anion type 1,3-dipoles) to the nitrile function linked to boron clusters.15 This reaction provides borylated 2,3dihydro-1,2,4-oxadiazoles under mild conditions and in good yields. However, no single example of CA of propargyl-allenyl anion type dipoles to borylated nitriles is known to date. In this work, we report on the reaction between nitrilium derivatives of the closo-decaborate anion with a propargyl-allenyl dipole such as the azide anion, which yields borylated C-substituted tetrazoles. Evident advances in the chemistry of tetrazoles are determined by their wide applications in medicine16 and as Received: September 6, 2013 Published: October 10, 2013 6576

dx.doi.org/10.1021/om400892x | Organometallics 2013, 32, 6576−6586

Organometallics

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Scheme 1. Studied Reactions

high-energy materials,17,18 components of ionic liquids,19 analytical reagents,20 corrosion inhibitors,21 catalysts,22 and many others. Thus, borylated tetrazoles could combine useful properties of both boron clusters and tetrazoles.

organic azides were previously reported for the Re6Se8 clusters bearing nitrile ligands.45,46 The reason for the different behavior of N3− and RN3 toward borylated nitriles is disclosed in the section devoted to theoretical study of the azide cycloaddition in this article. Alkylation of the Tetrazole Ring. We found that the corresponding 4-alkyl tetrazoles could be prepared from nitrilium derivatives of closo-decaborate anion by two distinct steps, namely, CA of the azide anion followed by alkylation of the obtained tetrazole. Borylated tetrazoles 2′a−d were obtained similarly to 2a−d, but without the addition of [Bun4N]Br. These species were alkylated by R′X (X = Br, I; Table 1) at RT for 72−170 h, yielding isomeric products 4a−d, 5, 6 and 4′a−d, 5′, 6′ (Scheme 2).

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RESULTS AND DISCUSSION 1,3-Dipolar Cycloaddition. The most common method for synthesis of tetrazoles is based upon cycloaddition of azides to nitriles. Reactions of azide ions with organic nitriles are usually conducted in polar aprotic solvents (DMF, DMSO) and at elevated temperatures (70−160 °C) and prolonged reaction times.23−25 This CA could be enhanced by Lewis acids (Zn or Al salts23,26,27) in catalytic amounts and/or by microwave irradiation.23 This activation allows the performance of CA in water or water/alcohol mixtures, but usually prolonged heating is still necessary. Metal-mediated CA is also known, and it is typically conducted by two routes, viz., CA of free azides to coordinated nitriles (for recent works see refs 28−31) or metalbound azides to uncomplexed nitriles (for recent works see refs 32−35). Some metal-mediated syntheses allow the generation of coordinated tetrazoles rapidly already at room temperature (RT).28,31 Furthermore, CAs of azide ions to highly reactive alkylnitrilium salts were reported, and these reactions form 1,5disubstituted tetrazoles at RT.36,37 Several cases of BF3catalyzed CA of azides to nitriles, except one example of intramolecular CA,38 require prolonged heating, and they are not recommended for synthetic purposes.39−41 For this work we addressed four closo-decaborates [Bun4N][B10H9(NCR)] (R = Me 1a, Et 1b, But 1c, Ph 1d) and also NaN3 as the most common source of azide ions. The reaction between the clusters [Bun4N][B10H9(NCR)] in MeCN solution and the solid NaN3 proceeds under mild conditions (RT, 15 h) to afford CA products 2a−d (88−96% isolated yields) (Scheme 1, A). The reaction of 1a−d with bis(triphenylphosphine)iminium azide [Ph3PNPPh3]N3 ([PPN]N3) proceeds immediately upon mixing acetonitrile solutions of the starting materials at RT, giving quantitativelyas verified by 1H NMR spectroscopythe corresponding borylated tetrazoles. In 1H NMR and high-resolution ESI-MS, no signals corresponding to the starting materials were observed 2 min after mixing the reactants. Comparison of the experiments with NaN3 and [PPN]N3 indicates that most likely the reaction rate of 1a−d with NaN3 is limited by the rate of dissolution of NaN3 in MeCN. All our attempts to carry out CA of alkyl or aryl azides (pMe-C6H4-COCH2N3, p-NO2-C6H4-CH2N3, PhN3) to borylated nitriles 1a−d were unsuccessful. Under the conventional conditions for CA of organic azide to activated nitriles42−44 (2 d, dry EtCN, 100 °C, under Ar) no traces of CA products were observed by high-resolution ESI-MS, while slow degradations of the starting nitrilium derivatives were detected. Similar differences in reactions of activated nitriles with azide ions and

Table 1. Compound Numbering for the Borylated Tetrazolium Salts and Ratio of Isomers (n/n′) in the Reaction Mixture nos.

R

R′

n/n′

4a (4′a) 4b (4′b) 4c (4′c) 4d (4′d) 5 (5′) 6 (6′)

Me Et But Ph Me Me

CH2C6H4NO2-p CH2C6H4NO2-p CH2C6H4NO2-p CH2C6H4NO2-p Me CH2COC6H4Me-p

3.7 2.7 0.1 3.6 4.0 3.7

The ratio of 1,4,5-substituted and 1,3,5-substituted isomers in the reaction mixture was determined by 1H NMR, and it depends mainly on steric hindrance of R (Table 1). The reaction rate also depends on substituents R. Thus, the alkylation of the tetrazole featuring the bulky But group (2′c) takes 170 h, while other reactions proceed for 72 h. Separation of the isomers was carried out by column chromatography on SiO2 to obtain pure isomers 4a,b, 5, 6 (54−62%) and 4′a−c, 5′, 6′ (16−69%), respectively. Isomers 4d and 4′d have almost equal retention values and were not separated even after the duly repeated column chromatography. Cation Metathesis. Compounds 3a−d were obtained in the metathetical reaction between each of 2a−d and NaBPh4 in methanol/water solution (Scheme 1, B). Sodium salts 3a−d were isolated as colorless solids after separation of the solid [Bun4N]BPh4 followed by evaporation of the solvent and crystallization of the resulting oily residues in a desiccator (ca. 95% yields). Characterization of the Borylated Tetrazoles. Borylated tetrazoles 2a−d, 3a−d, 4a,b, 5, 6, 4′a−c, 5′, and 6′ were characterized by ICP-MS based B analysis, high-resolution ESI± mass spectrometry, molar conductivity, IR, 1H, 13C{1H}, and 11 1 B{ H} NMR spectroscopy, and also X-ray diffraction (for 2c, 5, and 6′). All physicochemical data are in agreement with the 6577


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Scheme 2. Alkylation Reaction

weak broad singlet of the substituted boron atom B(2) was found between −11.6 and −13.8 ppm, and the other equatorial atoms emerged as multiple signals in the intervals between −24.0 and −26.6 ppm (B(3), B(5), B(6), B(9)) and −27.0 and −29.4 ppm (B(4), B(7), B(8)). All signals of the unsubstituted boron atoms split into doublets without the broadband 1H decoupling, while the substituted B(2) atom still gives a singlet. The presence of cross-peaks between C−CH3 and N−CH3 or N−CH2 groups in the 2D NOESY NMR spectrum of 4a and 5 confirms the suggested structure of the 1,4,5-substituted isomer.

proposed formulas. We also measured mp (decomposition) values of all obtained species. Microanalytical data for all synthesized compounds were found to depend on the equipment and catalysts used for the determinations, and the obtained results show poor convergence (ca. ±0.7%); this feature of organoboron compounds was repeatedly noticed in the past. The borylated tetrazoles give satisfactory ICP-MS-based B elemental analysis. In the ESI− mass spectra of 2a−d, the most intensive signals are due to 1/2[A]2− and [A + Bun4]− (where A− is the anion), while the ESI+ mass spectra of 2a−d exhibit intensive signals from [Bun4N]+. No signals from [Bun4N]+ were observed in the ESI+-MS of 3a−d, while weak signals of [A + 3Na]+ in the ESI+-MS and intensive signals of 1/2[A]2−, [A + H]−, and [A + Na]− in the ESI−-MS were detected. In the ESI mass spectra of 4a,b, 5, 6, 4′a−c, 5′, and 6′, only strong signals due to [A]− and [Bun4N]+ were detected in the negative and positive modes, respectively. For all spectra, the isotopic patterns agree well with the calculated ones. Molar conductivity ΛM values of 2a−d measured in ca. (4− 8) × 10−4 mol L−1 MeNO2 solutions are characteristic for ionic species of the [A2−][Q+]2 or [A−][Q+] type in this solvent (measured values for 2a−d: 158−167 Ω−1 cm2 mol−1, typical range:47 150−180 Ω−1 cm2 mol−1; measured values for 4a,b, 5, 6, 4′a−c, 5′, and 6′: 75−81 Ω−1 cm2 mol−1, typical range:47 75−95 Ω−1 cm2 mol−1). In the IR spectra, the most intensive bands observed in the range 3057−2465 cm−1 are due to ν(C−H) and ν(B−H) vibrations between 2563 and 2463 cm−1. In the spectra of 4a,b and 4′a−c, also two strong bands due to the stretching vibrations of the NO2 group at 1522−1524 cm−1 (asymm.) and at 1348 cm−1 (symm.) were observed. No ν(CN) stretches at ca. 2300 cm−1 specific for the starting nitrilium salts1 were observed in the IR spectra of 2a−d. The only peaks in the 1H NMR spectra of 2a−d and 3a−d, besides those from the tetrabutylammonium cation and very broad signals of BH protons, are the signals of the hydrocarbon substituent of the tetrazole ring. These resonances are downfield shifted compared to the starting nitrilium salts. The most characteristic peaks in the 1H NMR spectra of alkylated tetrazoles 4a,b, 5, 6, 4′a−c, 5′, and 6′ are from the NCH2 or NCH3 groups. Signals of the 1,4,5-isomers (4a,b, 5, and 6) are deshielded by ca. 0.3 ppm compared to the 1,3,5isomers (4′a−c, 5′, and 6′). This allows the determination of a ratio of isomers in the reaction mixture based on integration of signals of the corresponding groups. The most characteristic signal in the 13C{1H} NMR spectra of the borylated tetrazoles is the C(1)N resonance, which falls in the interval 153.5− 171.6 ppm. The 11B{1H} NMR confirmed the closo-decaborane structure of 2a−d and 3a−d. Two singlets from the apical boron atoms B(10) and B(1) were observed in the range from 1.4 to −0.2 ppm and from −1.5 to −3.9 ppm, respectively. The

Table 2. Selected Bond Lengths [Å] and Angles [deg] for Borylated Tetrazoles 2c, 5, and 6′ parameter

2c

N(1)−B(2) N(1)−C(5) N(1)−N(2) N(2)−N(3) N(3)−N(4) N(4)−C(5) C(5)−C(6) N(4)−C(7) N(3)−C(12)

1.5517(13) 1.3548(13) 1.3592(12) 1.2979(13) 1.3537(14) 1.3295(14) 1.5164(15)

C(5)−N(1)−B(2) C(5)−N(1)−N(2) N(2)−N(1)−B(2) N(3)−N(2)−N(1) N(2)−N(3)−N(4) C(5)−N(4)−N(3) N(4)−C(5)−N(1) N(4)−C(5)−C(6) N(1)−C(5)−C(6) N(3)−N(4)−C(7) N(5)−N(4)−C(7) N(2)−N(3)−C(12) N(4)−N(3)−C(12)

137.29(9) 106.70(8) 115.39(8) 107.86(8) 110.24(8) 106.33(9) 108.85(9) 121.55(9) 129.59(9)

5 1.555(2) 1.327(2) 1.367(2) 1.287(2) 1.349(2) 1.335(2) 1.474(3) 1.462(2)

6′ 1.5437(15) 1.3536(15) 1.3307(13) 1.3062(14) 1.3324(14) 1.3266(16) 1.4844(17) 1.4546(14)

129.62(15) 108.70(14) 121.68(14) 108.44(14) 107.25(14) 110.07(14) 105.53(16) 126.52(16) 127.95(15) 120.49(15) 129.43(16)

130.64(10) 108.74(9) 120.21(9) 103.65(9) 115.35(10) 102.50(9) 109.77(10) 125.32(11) 124.91(11)

120.35(10) 124.21(10)

The single-crystal X-ray diffraction studies conducted for 2c, 5, and 6′ (Figures 1, 2) indicate the presence of three (2c) or two (5 and 6′) independent ionic parts. All bond lengths and angles of the cationic parts are the same, within 3σ, as those previously described in the literature.15,48 The anionic parts of 2c, 5, and 6′ consist of the closo-decaborate cluster linked to the substituted tetrazole ring via the N(1) atom. In the cluster part, the B−B bond distances and angles are typical for 2substituted-nonahydro-closo-decaboron clusters.1,48 The bond lengths N(1)−B(2) are equal, within 3σ, to those in the starting borylated nitrile.49 Bond distances and angles of the heterocyclic ring of 2c are typical for 1,5-disubstituted 6578


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In contrast, the mechanism of CA of the azide ion N3− to 1aT is stepwise involving the formation of zwitterionic acyclic intermediate INT via TS31 followed by a ring closure via TS32 (Scheme 3). The rate-determining step of the reaction is the first one (Figure 4). It is interesting that in accord with the previous DFT computational data60−64 the mechanism of the reactions R′N3 + RCN and N3− + RCN (R = Me, Ph, tBu, MeS, MeO, CH2F, CHF2, CF3, Me3SiN3; R′ = Me, H) is concerted. The switch of the mechanism to the stepwise one in the case of the reaction N3− + 1aT may be interpreted in terms of electrostatic arguments. The effective NBO atomic charges on the C(2) and N(1) atoms of 1aT and RCN are positive and negative, respectively (Figure 5), indicating that the C(2) atom is an electrophilic center, while the N(1) atom is a nucleophilic center. The NBO charges on the terminal and the R′-bound N atoms in R′N3 (R′ = Me, Ph) are negative [(−0.04)−(−0.07) and (−0.32)−(−0.34) e, respectively], and the charge on the terminal N atoms in N3− is even more negative (−0.56 e). Upon the CAs of R′N3 or N3− to nitriles, the C(2) and N(3) atoms exhibit an electrostatic attraction, whereas the N(1) and N(5) atoms exhibit an electrostatic repulsion (Figure 5). Such interactions explain the asynchronicity of these CAs with prior formation of the C(2)N(3) bond. Since the linkage of the RCN group with the boron cluster [B10H9]− enhances significantly the positive charge on the C(2) nitrile atom (from 0.28 to 0.43 e, R = Me), the C(2)N(3) attraction is the highest in the case of the reaction N3− + 1aT, while the N(1)N(5) repulsion is also very efficient for this process, accounting for the switch of the reaction mechanism from the concerted to the stepwise. In fact, the first step of the reaction N3− + 1aT represents the nucleophilic addition of N3− at the electrophilic C atom of the borylated nitrile, and the azide ion serves as a nucleophile in this process rather than a 1,3-dipole. A similar stepwise mechanism was previously proposed for the reaction between N3− and RCN−BH3 (R = Me, CH2F, CHF2, CF3) on the basis of ab initio HF and MP2 calculations.65 ii. Activation and Reaction Energies. An inspection of the calculated activation and reaction energies (in terms of ΔG⧧ and ΔG in the gas phase and MeCN solution) indicates the following. First, the gas-phase activation barrier of the reaction N3− + 1aT is clearly higher than that of the R′N3 + 1aT cycloadditions (Table 4). This result is not surprising taking into account the fact that the reaction occurs between two anions in the former case and between an anion and a neutral molecule in the latter case. However, after consideration of the solvent effects, the activation barrier of the reaction N3− + 1aT becomes significantly lower than that of the reactions R′N3 + 1aT (Figure 4). The great stabilization of dianionic transition states TS31 and TS32 upon solvation is responsible for such a

Figure 1. ORTEP view of borylated tetrazole 2c with the atomic numbering scheme (thermal ellipsoids are drawn at the 50% probability level; cations are omitted for clarity).

tetrazoles.50,51 In the tetrazole ring of 5, the bond lengths C(5)−N(4) (1.335(2) Å) and C(5)−N(1) (1.327(2) Å) are equal, while the N(2)−N(3) bond (1.287(2) Å) is shorter than N(1)−N(2) (1.367(2) Å) or N(3)−N(4) (1.349(2) Å). In 6′, the C(5)−N(4) bond is shorter (1.3266(16) Å) than C(5)− N(1) (1.3536(15) Å), but, in contrast to 5, the shortest nitrogen−nitrogen bond is N(2)−N(3) (1.3062(14) Å). This determines the single/double-bond arrangement in tetrazole rings of 5 and 6′, drawn in Scheme 2. Such bond allocation is typical for 1,4,5-52,53 and 1,3,5-trisubstituted54,55 tetrazoles. All other bonds and angles are of normal values. Theoretical Study of the Azide Cycloaddition. With the aim to interpret the different chemical behavior of the azide ion and organic azides toward the borylated nitriles, quantum chemical calculations of hypothetical CAs of MeN3, PhN3, and CA of N3− to the [B10H9(NCMe)]− (1aT) cluster have been carried out at the DFT level. i. Reaction Mechanisms. In accord with computational results, the concerted mechanism was found for both ortho- and meta-regioisomeric pathways of CAs between R′N3 (R′ = Me, Ph) and 1aT, leading to 1,4,5- and 1,2,5-substituted tetrazoles 5T, 9T and 5T″, 9T″, respectively (Scheme 3). This mechanism includes the formation of one transition state for each regioisomeric pathway (TS1O, TS2O and TS1M, TS2M; Figure 3). The topological analysis of the electron density distribution (AIM) indicates that these transition states have a cyclic nature. Indeed, the bond critical points for both N(1)··· N(5) and C(2)···N(3) contacts as well as the ring critical point were located (Table 3). The mechanism is clearly asynchronous with the C(2)N(3) bond formation preceding the N(1)N(5) bond formation. The calculated parameter Sy proposed as a quantitative measure of the synchronicity of concerted CAs56−59 is 0.65−0.70 and 0.57−0.66 for the ortho- and meta-CAs, respectively (Sy is 0 for the stepwise CAs and Sy is 1 for the fully concerted CAs).

Figure 2. ORTEP view of trisubstituted tetrazoles 5 and 6′ with the atomic numbering scheme (thermal ellipsoids are drawn at the 50% probability level; cations are omitted for clarity). 6579


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Scheme 3. Mechanisms of the Azide CAs to Borylated Acetonitrile 1aT

Figure 3. Equilibrium structures of the transition states and the intermediate.

Figure 4. Energy profiles of the azide CAs to the borylated nitrile 1aT calculated at the M06-2X level.

Table 3. Most Important Characteristics of Transition States Calculated at the B3LYP Levela NPA νi ΔWI Sy ρC(2)N(3) ρN(1)N(5) HbC(2)N(3) HbN(1)N(5)

TS1O

TS1M

TS2O

TS2M

0.08 430i 0.29 0.65 0.714 0.163 −0.254 0.023

−0.22 404i 0.40 0.57 0.741 0.092 −0.256 0.014

0.04 416i 0.25 0.70 0.683 0.221 −0.231 0.020

−0.28 375i 0.42 0.66 0.741 0.075 −0.255 0.011

TS31

TS32

0.34 118i

0.59 255i

0.493

1.606 0.233 −1.470 0.022

−0.101

are −69.7 kcal/mol (N3−) and −47.4 kcal/mol (1aT). Thus, the experimentally observed higher reactivity of the azide ion toward the borylated nitriles in comparison with organic azides is mostly accounted for by the solvent effects. Second, the activation barriers ΔGs⧧ of the reactions R′N3 + 1aT calculated at the B3LYP level (34.2−45.8 kcal/mol) are higher than the activation energy of the reaction between nitrone PhCHN+(Me)O− and MeCN estimated using the same functional and similar basis set (34.1 kcal/mol).66 Taking into account that CA between nitrones and free acetonitrile does not occur even under harsh conditions,67−69 the reaction between R′N3 and 1aT also should not be realized, and this is in accord with the experimental observations. Third, the low activation energy of the reaction N3− + 1aT correlates with the fact that this CA occurs very fast at room temperature. Fourth, all CAs discussed here are significantly exoergonic except meta-CA of PhN3. In the latter case, the ΔGs value is less negative conceivably due to a steric repulsion between the Ph group and the boron cluster. Thus, CAs of azides to 1aT are controlled by kinetic rather than by

a

NPA charge transfer from azide to nitrile (NPA, e), imaginary frequencies (νi), synchronicity (Sy), difference of the Wiberg bond indices (ΔWI) for the C(2)···N(3) and N(1)···N(5) contacts, electron densities (ρ, e/Å3), and energy densities (Hb, hartree/Å3) for the bond critical points of these contacts.

switch of the reactivity of N3− and R′N3 from gas phase to solution. Indeed, the solvent effect of TS31 in MeCN solution (M06-2X) is −139.8 kcal/mol, whereas those of the reactants 6580


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Figure 5. Effective NBO atomic charges on the reacting atoms of azides and nitriles.

(e.g., azides60,61,63) to RCN species, the reaction is strongly facilitated and could be conducted rapidly and under mild conditions upon a linkage of the nitrile N atom either to boron centers or to some metals.28,31 The calculations performed in this work indicated that the experimentally observed higher reactivity of the azide ion toward the borylated nitriles compared to the organic azides (where this reaction was not observed) is mostly accounted for by the solvent effects, and, eventually, CAs of azides to [B10H9(NCMe)]− are controlled by kinetic rather than by thermodynamic factors. We also demonstrated that the borylated tetrazoles could be functionalized by alkylation, yielding 1,4,5- and 1,3,5-trisubstituted isomers, which were separated by column chromatography. The ratio of 3- and 4-substituted tetrazole and the reaction rate depend mostly on steric hindrance of the substituent at the carbon atom of the tetrazole ring: increasing the R bulkiness decreases the reaction rate and the content of the 4-isomers. In addition, tetrazoles bound to closo-decaborate anions were converted by the cation metathesis reaction to a water-soluble form suitable for biological investigations, and works in this direction are under way in our group.

Table 4. Calculated Gibbs Free Energies of Activation and Reaction (in kcal/mol) in the Gas Phase and MeCN Solution (in parentheses) ΔG⧧

ΔG

reaction

B3LYP

M062X

MeN3 + 1aT → 5T via TS1O

39.6 (34.2) 31.8 (43.3) 42.1 (39.8) 30.0 (45.8) 46.0 (18.3) 7.8 (6.8)

34.4 (25.9) 35.7 (39.2) 37.4 (33.8) 34.9 (50.8) 41.2 (15.1) 10.5 (9.7)

MeN3 + 1aT → 5T″ via TS1M PhN3 + 1aT → 9T via TS2O PhN3 + 1aT → 9T″ via TS2M N3− + 1aT → INT via TS31 INT → 2aT via TS32

B3LYP

M06-2X

−7.2 (−15.9) −13.2 (−11.4) −1.8 (−11.7) −1.1 (−1.0) 42.1 (5.9) −27.1 (−21.3)

−24.9 (−32.1) −31.5 (−28.3) −18.4 (−26.7) −19.7 (−18.4) 32.0 (−4.1) −35.1 (−27.7)

thermodynamic factors. Fifth, the 1,4,5-substituted regioisomer of the tetrazole products 5T and 9T are more thermodynamically stable than the corresponding 1,2,5-substituted isomers 5T″ and 9T″. This is coherent with the experimentally observed formation of 5 and 5′ but not 5″ upon the alkylation of 2′a. Final Remarks. We observed the first example of cycloaddition of a propargyl-allenyl anion type dipole, viz., N3−, to the CN functionality linked to any boron clusters. In solution, CA proceeds rapidly, giving borylated tetrazoles under mild conditions in excellent yields. Our experiments suggest that the CN group of the boron cluster is strongly activated toward CA of N3− as compared to the CN group in the conventional alkyl- and arylnitriles. Moreover, the reactivity of the borylated nitrile functionality in CA is comparable to the most reactive compounds featuring the CN group, viz., Nalkyl nitrilium salts, which also react with azide ions at room temperature.36,37 In contrast to N3−, alkyl or aryl azides RN3 do not undergo CA to nitrilium borates even under harsh conditions. Theoretical studies at the DFT level of theory revealed that the mechanism of hypothetical CA of the organic azides R′N3 (R′ = Me, Ph) to the borylated acetonitrile [B10H9(NCMe)]− is concerted asynchronous, whereas that for the reaction of N3− is stepwise; such a switch of the reaction mechanism may be explained in terms of the electrostatic arguments. In general, as can be inferred from inspection of the theoretical and relevant synthetic works on CA of propargyl-allenyl anion type dipoles

■

EXPERIMENTAL SECTION

Instrumentation and Materials. NaN3, organic reagents, and the employed solvents were obtained from commercial sources and used as received. closo-Decaborate clusters 1a,70 1b, 1c,15 and 1d3 were prepared in accord with the published methods. [PPN]N3 was obtained by the literature method from [PPN]Cl71 and NaN3.72 Elemental analysis for boron was performed by the FSUE IREA 291 Center (Moscow) on a iCAP 6300 Duo ICP spectrometer using In 292 as an internal standard. Electrospray ionization mass spectra were obtained on a Bruker micrOTOF spectrometer equipped with electrospray ionization (ESI) source, and MeOH and MeCN were used as the solvents. The instrument was operated at both positive and negative ion modes using an m/z range of 50−3000. In the isotopic pattern, the most abundant peak is reported. Infrared spectra were recorded on a Shimadzu FTIR 8400S instrument in KBr pellets. 1H, 13 C{1H}, and 11B{1H} NMR spectra were measured on a Bruker-DPX 300 spectrometer at ambient temperature; BF3·Et2O was used as the external standard for 11B{1H} NMR. Molar conductivities of 10−3− 10−4 M solutions in MeNO2 were measured on a Mettler Toledo FE30 conductometer using an Inlab710 sensor. Melting points were determined in a capillary on a Stuart SMP30 melting point apparatus. X-ray Diffraction Studies. The crystals of the studied compounds were obtained by a slow evaporation of PriOH/H2O (2c), acetone/ Pri2O (5), or MeCN/butyl propionate (6′) solutions at RT. Transparent colorless crystals were fixed on a micromount and placed on an Agilent Technologies Excalibur Eos (5) and Agilent Technologies SuperNova (2c and 6′) (Oxford Diffraction) diffrac6581


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tometer and measured at 100 K using monochromated Mo Kα (5) and Cu Kα (2c and 6′) radiation. The structures were solved by the direct methods and refined with |Fo| ≥ 4σF by means of the SHELXL97 program73 incorporated in the OLEX2 program package74 (Table S1). Carbon- and nitrogen-bonded H atoms were placed in calculated positions and were included in the refinement in the “riding” model approximation, with Uiso(H) set to 1.5Ueq(C) and C−H = 0.96 Å for the methyl groups, 1.2Ueq(C) and C−H = 0.98 Å for the tertiary CH groups, 1.2Ueq(C) and C−H = 0.93 Å for the carbon atoms of the benzene rings, and 1.2Ueq(B) and B−H = 1.10 Å for the boron atoms of the boron cluster fragments. Absorption correction was applied in the CrysAlisPro75 program complex using a multifaceted crystal model based on expressions derived by R. C. Clark and J. S. Reid.76 Supplementary crystallographic data for these compounds have been deposited at the Cambridge Crystallographic Data Centre (CCDC 950326 for 2c, 950324 for 5, and 950325 for 6′) and can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif. Computational Details. The full geometry optimization of all structures and transition states has been carried out at the DFT level of theory using the B3LYP77,78 and M06-2X79 functionals with the help of the Gaussian 0980 program package. The B3LYP functional was applied in a number of previous theoretical studies of CAs to nitriles,13,62−64,81−83 and we selected this functional for this work to make possible the comparison of the current results with those obtained previously. The M06-2X functional was chosen as one of the most reliable functionals adequately accounting for the dispersion forces,84,85 which may be rather important in the systems under study. The geometry optimization was carried out using the 6-311+G(d) basis set. No symmetry operations have been applied. Stability tests were carried out using the keyword STABLE in Gaussian 09. The basis set superposition error was not estimated because it weakly affects the activation and reaction energies of cycloadditions to nitriles.81,82 The Hessian matrix was calculated analytically for the optimized structures in order to prove the location of correct minima (no imaginary frequencies) or saddle points (only one imaginary frequency) and to estimate the thermodynamic parameters, the latter being calculated at 25 °C. The nature of all transition states was investigated by the analysis of vectors associated with the imaginary frequency and by the calculations of the intrinsic reaction coordinates (IRC)86−89 followed by the geometry optimization from the last IRC points. Total energies corrected for solvent effects (Es) were estimated at the single-point calculations on the basis of gas-phase geometries using the polarizable continuum model in the CPCM version90,91 with MeCN as solvent and with consideration of dispersion, repulsion, and cavitation nonelectrostatic terms. The UAKS model was applied for the molecular cavity. The entropic term in solution (Ss) was calculated according to the procedure described by Wertz92 and Cooper and Ziegler93 (see Supporting Information for details). The enthalpies and Gibbs free energies in solution (Hs and Gs) were estimated as Hs = Es − Eg + Hg and Gs = Hs − TSs, where Es, Eg, and Hg are the total energies in solution and in gas phase and the gas-phase enthalpy. The Wiberg bond indices (Bi)94 and atomic charges were computed by using the natural bond orbital (NBO) partitioning scheme.95 The topological analysis of the electron density distribution with the help of the AIM method of Bader96 was performed using the program AIMAll.97 The synchronicity of CAs (Sy) was calculated using the formula reported previously56−59 (see Supporting Information). Boron-Mediated Cycloaddition. The reaction between NaN3 (23 mg, 0.35 mmol) and the borylated nitriles (1a−d; 0.30 mmol) was performed in acetonitrile (2 mL). The reaction mixture was vigorously stirred at RT, and completeness of the reaction was monitored by TLC. After 15 h [Bun4N]Br (97 mg, 0.30 mmol) was added to the reaction mixture followed by evaporation of the solvent to dryness under vacuum at 30 °C. CH2Cl2 (1 mL) was added to the residue, the formed suspension was filtered off, and the filtrate was evaporated to give an oily residue. The cycloaddition products were crystallized under a layer of diethyl ether at RT to furnish solid 2a−d. Yield: 197 mg (96%). Mp: 109−111 °C, dec. Anal. Found: B, 15.78. Calcd for C34H84N6B10: B, 15.6. High-resolution ESI+-MS, m/z:

242.2837 [Bun4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 101.1000 [A] 2− /2 (101.0997 calcd), 444.4930 [A + Bu n 4N]− (444.4840 calcd). ΛM (MeNO2, 4.6 × 10−4 mol L−1): 158 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2961 s, 2937 s, 2874 s ν(C−H), 2467 s ν(B−H), 1483 s, 1474 s, 1383 s ν(CN), ν(N N). 1H NMR (300.13 MHz, CDCl3): δ 3.18 (t, 16H, NCH2), 2.64 (s, 3H, CCH3), 1.67−1.52 (m, 16H, NCH2CH2Et), 1.50−1.35 (m, 16H, N(CH2)2CH2Me), 0.97 (t, 24H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (75.49 MHz, CD3CN): δ 156.3 (CN), 59.3 (NCH2Pr), 24.4 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3), 11.3 (CCH3). 11B{1H} NMR (96.32 MHz, CD3CN): δ −0.2 (B(10)), −2.8 (B(1)), −13.6 (B(2)), −24.8, −25.3 (B(3), B(5), B(6), B(9)), −28.4 (B(4), B(7), B(8)).

Yield: 185 mg (89%). Mp: 120−121 °C, dec. Anal. Found: B, 15.46. Calcd for C35H86N6B10: B, 15.5. High-resolution ESI+-MS, m/z: 242.2825 [Bun4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 108.1103 [A] 2− /2 (108.1074 calcd), 444.5051 [A + Bu n 4N]− (458.4997 calcd). ΛM (MeNO2, 5.4 × 10−4 mol L−1): 163 Ω−1 cm2 mol−1 IR spectrum in KBr, selected bands, cm−1: 2961 s, 2936 s, 2874 s ν(C−H), 2471 s ν(B−H), 1482 s, 1474 s, 1381 s ν(CN), ν(N N). 1H NMR (300.13 MHz, CDCl3): δ 3.26−3.08 (m, 18H, NCH2CH3 and NCH2Pr), 1.67−1.51 (m, 16H, NCH2CH2Et), 1.50−1.35 (m, 16H, N(CH2)2CH2Me), 1.31 (t, 3H, J = 8 Hz CCH2CH3), 0.97 (t, 24H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (75.49 MHz, CD3CN): δ 161.1 (CN), 59.4 (NCH2Pr), 24.4 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 18.7 (CCH2), 13.8 (N(CH2)3CH3), 13.1 (CCH2CH3). 11B{1H} NMR (96.32 MHz, CD3CN): δ −0.2 (B(10)), −2.8 (B(1)), −13.6 (B(2)), −24.8, −25.3 (B(3), B(5), B(6), B(9)), −28.3 (B(4), B(7), B(8)).

Yield: 198 mg (91%). Mp: 124−125 °C, dec. Anal. Found: B, 14.87. Calcd for C37H90N6B10: B, 14.4. High-resolution ESI+-MS, m/z: 242.2832 [Bun4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 122.1276 [A] 2− /2 (122.1231 calcd), 486.5304 [A + Bu n 4N]− (486.5310 calcd). ΛM (MeNO2, 4.7 × 10−4 mol L−1): 167 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2961 s, 2934 s, 2874 s ν(C−H), 2503 s, 2463 s ν(B−H), 1485 s, 1475 s, 1383 s ν(CN), ν(NN). 1H NMR (300.13 MHz CDCl3): δ 3.26 (t, 16H, NCH2), 1.69−1.54 (m, 25H, C(CH3)3 and NCH2CH2Et), 1.51−1.36 (m, 16H, N(CH2)2CH2Me), 0.97 (t, 24H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (75.49 MHz, CD3CN): δ 165.5 (CN), 59.4 (NCH2Pr), 32.5 (CCH 3 ) 3 ), 30.4 (CCH 3 ) 3 ), 24.4 (NCH 2 CH 2 Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3). 11B{1H} NMR (96.32 MHz, 6582


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CD3CN): δ 0.3 (B(10)), −1.5 (B(1)), −11.6 (B(2)), −24.0, −24.6 (B(3), B(5), B(6), B(9)), −27.1, −28.2 (B(4), B(7), B(8)).

(NCH2Pr), 52.2 (NCH2C6H4), 24.3 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3), 10.2 (CCH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 0.4 (B(10)), −3.8 (B(1)), −13.7 (B(2)), −25.3, −26.6 (B(3), B(5), B(6), B(9)), −29.3 (B(4), B(7), B(8)).

Yield: 197 mg (88%). Mp: 143−144 °C, dec. Anal. Found: B, 14.47. Calcd for C39H86N6B10: B, 14.3. High-resolution ESI+-MS, m/z: 242.2864 [Bun4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 132.1093 [A] 2−/2 (132.1074 calcd), 506.5041 [A + Bun 4 N] − (506.4997 calcd). ΛM (MeNO2, 4.5 × 10−4 mol L−1): 165 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2961 s, 2874 s ν(C− H), 2519 s, 2477 s ν(B−H), 1487 s, 1466 s, 1379 s ν(CN), ν(N N). 1H NMR (300.13 MHz, CD2Cl2): δ 7.86−7.79 (m, 2H, Ph), 7.46−7.39 (m, 3H, Ph), 3.16 (t, 16H, NCH2), 1.68−1.53 (m, 16H, NCH2CH2Et), 1.50−1.34 (m, 16H, N(CH2)2CH2Me), 1.00 (t, 24H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (75.49 MHz, CD3CN): δ 159.5 (CN), 131.5, 129.8, 129.7, 128.0 (Ph), 59.4 (NCH2Pr), 24.4 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3). 11 1 B{ H} NMR (96.32 MHz, CD3CN): δ 0.0 (B(10)), −2.5 (B(1)), −12.5 (B(2)), −24.4, (B(3), B(5), B(6), B(9)), −27.9, −28.7 (B(4), B(7), B(8)). Cation Metathesis. A solution of NaBPh4 in MeOH (0.5 mL) was added to a solution of 2a−d (0.15 mmol) in MeOH (0.5 mL) at RT. A precipitate formed immediately was filtered off, and water (5 mL) was added to the mother liquor. The mixture was cooled at 5 °C for 2 h and filtered off. The water solution was evaporated under vacuum at 35 °C to obtain an oily residue, which was crystallized as the colorless solid for 2 d in a desiccator over KOH. See Supporting Information for physicochemical data of 3a−d. Synthesis of 4a−b, 4′a−c, 5, 6, 5′, and 6′. Alkylating agent (0.25 mmol of BrCH2C6H4-NO2-p, BrCH2COC6H4-Me-p, or MeI) was added to a solution any of 2′a−d (0.16 mmol) in acetonitrile (0.5 mL). After 72 h (for 4a,b, 4′a,b, 5, 6, 5′, and 6′) or 170 h (for 4′c) at RT, solvent was evaporated under vacuum at 40 °C. The residue was dissolved in CH2Cl2, and a colorless precipitate was filtered off. Solvent was evaporated under vacuum at RT. Two isomers were separated on a SiO2 column using a CHCl3/acetone, 15:1, v/v, mixture as eluent. Oily residues were crystallized under Et2O (two 2 mL portions) and hexane (three 2 mL portions) layers to give the products as colorless (1,4,5-isomers) or light yellow (1,3,5-isomers) solids.

Yield: 17 mg (18%). Mp: 76−78 °C, dec. Anal. Found: B, 18.9. Calcd for C25H54N6B10O2: B, 18.68. High-resolution ESI+-MS, m/z: 242.2852 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 338.2412 [A]− (338.2391 calcd). ΛM (MeNO2, 5.7 × 10−4 mol L−1): 81 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2935 s, 2874 s ν(C−H), 2482 s ν(B−H), 1522 s, 1348 s ν(NO2). 1H NMR (300.13 MHz, CD3CN): δ 8.25 (d, 2H, J = 9 Hz, ortho to NO2 in Ph), 7.61 (d, 2H, J = 9 Hz, meta to NO2 in Ph), 5.87 (s, 2H, CH2C6H4), 3.10 (t, 8H, NCH2Pr), 2.70 (s, 3H, CCH3), 1.69−1.55 (m, 8H, NCH2CH2Et), 1.45−1.29 (m, 8H, N(CH2)2CH2Me), 0.98 (t, 12H, J = 7 Hz, N(CH2)3CH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 1.1 (B(10)), −3.7 (B(1)), −13.4 (B(2)), −25.1, −26.5 (B(3), B(5), B(6), B(9)), −28.2, −29.1 (B(4), B(7), B(8)).

Yield: 51 mg (54%). Mp: 186−188 °C, dec. Anal. Found: B, 18.5. Calcd for C26H56N6B10O2: B, 18.23. High-resolution ESI+-MS, m/z: 242.2838 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 352.2578 [A]− (352.2547 calcd). ΛM (MeNO2, 6.0 × 10−4 mol L−1): 80 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2937 s, 2876 s ν(C−H), 2480 s ν(B−H), 1524 s, 1348 s ν(NO2). 1H NMR (400.13 MHz, CD3CN): δ 8.22 (d, 2H, J = 9 Hz, ortho to NO2 in Ph), 7.55 (d, 2H, J = 9 Hz, meta to NO2 in Ph), 5.61 (s, 2H, CH2C6H4), 3.37 (q, 2H, J = 8 Hz, CCH2CH3), 3.08 (t, 8H, NCH2Pr), 1.60 (qv, 8H, NCH2CH2Et), 1.35 (sx, 8H, N(CH2)2CH2Me), 1.20 (t, 3H, J = 8 Hz, CCH2CH3), 0.96 (t, 12H, J = 7 Hz, N(CH2)3CH3). 13 C{1H} NMR (100.61 MHz, CD3CN): δ 156.8 (CN), 149.3 (ipso to NO2 in Ph), 140.1 (para to NO2 in Ph), 130.8 (meta to NO2 in Ph), 125.0 (ortho to NO2 in Ph), 59.3 (NCH2Pr), 52.0 (NCH2C6H4), 24.3 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 16.8 (CCH2CH3), 13.8 (N(CH2)3CH3), 11.5 (CCH2CH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 0.7 (B(10)), −3.6 (B(1)), −13.5 (B(2)), −25.2, −26.6 (B(3), B(5), B(6), B(9)), −29.0 (B(4), B(7), B(8)).

Yield: 54 mg (58%). Mp: 175−177 °C, dec. Anal. Found: B, 18.7. Calcd for C25H54N6B10O2: B, 18.68. High-resolution ESI+-MS, m/z: 242.2847 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 338.2415 [A]− (338.2391 calcd). ΛM (MeNO2, 7.9 × 10−4 mol L−1): 78 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2934 s, 2874 s ν(C−H), 2480 s ν(B−H), 1522 s, 1348 s ν(NO2). 1H NMR (300.13 MHz, CD3CN): δ 8.24 (d, 2H, J = 9 Hz, ortho to NO2 in Ph), 7.57 (d, 2H, J = 9 Hz, meta to NO2 in Ph), 5.60 (s, 2H, CH2C6H4), 3.11 (t, 8H, NCH2Pr), 2.80 (s, 3H, CCH3), 1.71−1.56 (m, 8H, NCH2CH2Et), 1.45−1.29 (m, 8H, N(CH2)2CH2Me), 0.98 (t, 12H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (75.49 MHz, CD3CN): δ 153.5 (CN), 149.3 (ipso to NO2 in Ph), 139.8 (para to NO2 in Ph), 131.0 (meta to NO2 in Ph), 125.0 (ortho to NO2 in Ph), 59.3

Yield: 20 mg (21%). Mp: 74−76 °C, dec. Anal. Found: B, 18.6. Calcd for C26H56N6B10O2: B, 18.23. High-resolution ESI+-MS, m/z: 242.2843 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 352.2559 [A]− (352.2547 calcd). ΛM (MeNO2, 4.9 × 10−4 mol L−1): 79 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2935 s, 2874 s ν(C−H), 2482 s ν(B−H), 1523 s, 1348 s ν(NO2). 1H NMR (400.13 MHz, CD3CN): δ 8.23 (d, 2H, J = 9 Hz, ortho to NO2 in Ph), 7.59 (d, 2H, J = 9 Hz, meta to NO2 in Ph), 5.85 (s, 2H, CH2C6H4), 3.19 (q, 2H, J = 8 Hz, CCH2CH3), 3.08 (t, 8H, NCH2Pr), 1.60 (qv, 8H, NCH2CH2Et), 1.35 (sx, 8H, N(CH2)2CH2Me), 1.28 (t, 6583


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CD3CN): δ 153.4 (CN), 59.3 (NCH2Pr), 35.8 (NCH3), 24.3 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3), 9.8 (CCH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 0.3 (B(10)), −3.9 (B(1)), −13.8 (B(2)), −25.4, −26.7 (B(3), B(5), B(6), B(9)), −29.5 (B(4), B(7), B(8)).

3H, J = 8 Hz, CCH2CH3), 0.96 (t, 12H, J = 7 Hz, N(CH2)3CH3). 13 C{1H} NMR (100.61 MHz, CD3CN): δ 166.6 (CN), 149.5 (ipso to NO2 in Ph), 139.4 (para to NO2 in Ph), 131.2 (meta to NO2 in Ph), 125.0 (ortho to NO2 in Ph), 59.3 (NCH2Pr), 58.3 (NCH2C6H4), 24.3 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 19.2 (CCH2CH3), 13.8 (N(CH2)3CH3), 11.6 (CCH2CH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 1.1 (B(10)), −3.6 (B(1)), −13.5 (B(2)), −25.1, −26.5 (B(3), B(5), B(6), B(9)),−28.9 (B(4), B(7), B(8)).

Yield: 12 mg (16%). Mp: 80−83 °C, dec. Anal. Found: B, 23.0. Calcd for C19H51N5B10: B, 23.63. High-resolution ESI+-MS, m/z: 242.2850 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 217.2237 [A]− (217.2227 calcd). ΛM (MeNO2, 5.1 × 10−4 mol L−1): 75 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2957 s, 2932 s, 2874 s ν(C−H), 2480 s ν(B−H), 1472 s ν(CN), ν(NN). 1 H NMR (300.13 MHz, CD3CN): 4.25 (s, 3H, NCH3), 3.11 (t, 8H, NCH2CH2), 2.70 (s, 3H, CCH3), 1.70−1.55 (m, 8H, NCH2CH2Et), 1.45−1.30 (m, 8H, NCH2CH2CH2Me), 0.99 (t, 16H, J = 7 Hz, N(CH2)3CH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 0.8 (B(10)), −3.8 (B(1)), −13.6 (B(2)), −25.2, −26.5 (B(3), B(5), B(6), B(9)), −28.4, −29.1 (B(4), B(7), B(8)).

Yield: 69 mg (69%). Mp: 72−74 °C, dec. Anal. Found: B, 17.7. Calcd for C28H60N6B10O2: B, 17.41. High-resolution ESI+-MS, m/z: 242.2847 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 380.2882 [A]− (380.2860 calcd). ΛM (MeNO2, 7.4 × 10−4 mol L−1): 76 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2934 s, 2874 s ν(C−H), 2486 s ν(B−H), 1524 s, 1348 s ν(NO2). 1H NMR (300.13 MHz, CD3CN): δ 8.25 (d, 2H, J = 8 Hz, ortho to NO2 in Ph), 7.55 (d, 2H, J = 8 Hz, meta to NO2 in Ph), 5.82 (s, 2H, CH2C6H4), 3.10 (t, 8H, NCH2Pr), 1.69−1.54 (m, 17H, NCH2CH2Et and C(CH3)3), 1.35 (sx, 8H, N(CH2)2CH2Me), 0.98 (t, 12H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (100.61 MHz, CD3CN): δ 171.6 (CN), 149.5 (ipso to NO2 in Ph), 139.4 (para to NO2 in Ph), 131.2 (meta to NO2 in Ph), 124.9 (ortho to NO2 in Ph), 59.3 (NCH2Pr), 58.1 (NCH2 C6 H4), 34.0 (C(CH3) 3), 29.0 ((C(CH3 )3 ), 24.3 (NCH2CH2Et), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3). 11 1 B{ H} NMR (128.38 MHz, CD3CN): δ 1.4 (B(10)), −2.4 (B(1)), −11.3 (B(2)), −24.4, −25.6 (B(3), B(5), B(6), B(9)), −27.7 (B(4), B(7), B(8)).

Yield: 57 mg (62%). Mp: 165−168 °C, dec. Anal. Found: B, 18.7. Calcd for C27H57N5B10O: B, 18.77. High-resolution ESI+-MS, m/z: 242.2843 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 335.2663 [A]− (335.2646 calcd). ΛM (MeNO2, 8.0 × 10−4 mol L−1): 77 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2935 s, 2874 s ν(C−H), 2478 s ν(B−H), 1695 s ν(CO), 1605 s, 1474 s ν(CN), ν(NN). 1H NMR (400.13 MHz, CD3CN): δ 7.93 (d, 2H, J = 8 Hz, ortho to CO in Ph), 7.41 (d, 2H, J = 8 Hz, meta to CO in Ph), 5.98 (s, 2H, CH2CO), 3.09 (t, 16H, NCH2CH2), 2.70 (s, 3H, CCH3), 2.44 (s, 3H, C6H4CH3), 1.61 (qu, 16H, NCH2CH2Et), 1.36 (sx, 16H, N(CH2)2CH2Me), 0.97 (t, 24H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (100.61 MHz, CD3CN): δ 189.5 (CO), 154.7 (CN), 147.4 (ipso to Me in Ph), 131.8 (para to Me in Ph) 130.6, 129.6 (ortho and meta to Me in Ph), 59.3 (NCH2Pr), 55.6 (CH2CO), 24.3 (NCH2CH2Et), 21.8 (C6H4CH3), 20.3 (N(CH2)2CH2Me), 13.8 (N(CH2)3CH3), 10.0 (CCH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 0.5 (B(10)), −3.9 (B(1)), −13.6 (B(2)), −25.2, −26.5 (B(3), B(5), B(6), B(9)), −29.4 (B(4), B(7), B(8)).

High-resolution ESI+-MS, m/z: 242.2854 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 400.2536 [A]− (400.2547 calcd). 1H NMR (400.13 MHz, CD3CN): δ 8.22−7.29 (signals of aromatic protons) 5.93 (s, 2H, CH2C6H4 of 1,3,5-isomer) 5.44 (s, 2H, CH2C6H4 of 1,4,5-isomer), 3.08 (t, 8H, NCH2Pr), 1.60 (qv, 8H, NCH2CH2Et), 1.35 (sx, 8H, N(CH2)2CH2Me), 0.99 (t, 12H, J = 7 Hz, N(CH2)3CH3).

Yield: 42 mg (58%). Mp: 135−137 °C, dec. Anal. Found: B, 23.1. Calcd for C19H51N5B10: B, 23.63. High-resolution ESI+-MS, m/z: 242.2849 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 217.2234 [A]− (217.2227 calcd). ΛM (MeNO2, 4.8 × 10−4 mol L−1): 76 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2961 s, 2943 s, 2872 s ν(C−H), 2513 s, 2474 s, 2459 s ν(B−H), 1472 s ν(CN), ν(NN). 1H NMR (300.13 MHz, CD3CN): 3.92 (s, 3H, NCH3), 3.11 (t, 8H, NCH2CH2), 2.75 (s, 3H, CCH3), 1.71−1.54 (m, 8H, NCH2CH2Et), 1.47−1.29 (m, 8H, N(CH2)2CH2Me), 0.99 (t, 16H, J = 7 Hz, N(CH2)3CH3). 13C{1H} NMR (100.61 MHz,

Yield: 18 mg (20%). Mp: 156−159 °C, dec. Anal. Found: B, 19.3. Calcd for C27H57N5B10O: B, 18.77. High-resolution ESI+-MS, m/z: 242.2850 [Bu4N]+ (242.2848 calcd). High-resolution ESI−-MS, m/z: 335.2671 [A]− (335.2646 calcd). ΛM (MeNO2, 6.4 × 10−4 mol L−1): 80 Ω−1 cm2 mol−1. IR spectrum in KBr, selected bands, cm−1: 2962 s, 2936 s, 2874 s ν(C−H), 2482 s ν(B−H), 1697 s ν(CO), 1605 s, 1474 s, 1458 s ν(CN), ν(NN). 1H NMR (400.13 MHz, CD3CN): δ 7.88 (d, 2H, J = 8 Hz, ortho to CO in Ph), 7.39 (d, 2H, J 6584


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= 8 Hz, meta to CO in Ph), 6.20 (s, 2H, CH2CO), 3.08 (t, 16H, NCH2Pr), 2.76 (s, 3H, CCH3), 2.43 (s, 3H, C6H4CH3), 1.60 (qu, 16H, NCH2CH2Et), 1.35 (sx, 16H, N(CH2)2CH2Me), 0.96 (t, 24H, J = 7 Hz, N(CH2)3CH3). 11B{1H} NMR (128.38 MHz, CD3CN): δ 1.1 (B(10)), −3.7 (B(1)), −13.4 (B(2)), −25.1, −26.5 (B(3), B(5), B(6), B(9)), −28.2, −29.1 (B(4), B(7), B(8)).

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(11) Kritchenkov, A. S.; Bokach, N. A.; Kuznetsov, M. L.; Dolgushin, F. M.; Tung, T. Q.; Molchanov, A. P.; Kukushkin, V. Y. Organometallics 2012, 31, 687−699. (12) Bokach, N. A.; Balova, I. A.; Haukka, M.; Kukushkin, V. Y. Organometallics 2011, 30, 595−602. (13) Kuznetsov, M. L.; Kukushkin, V. Y.; Pombeiro, A. J. L. J. Org. Chem. 2010, 75, 1474−1490. (14) Luzyanin, K. V; Tskhovrebov, A. G.; Guedes da Silva, M. F. C.; Haukka, M.; Pombeiro, A. J. L.; Kukushkin, V. Y. Chem.Eur. J. 2009, 15, 5969−5978. (15) Mindich, A. L.; Bokach, N. A.; Dolgushin, F. M.; Haukka, M.; Lisitsyn, L. A.; Zhdanov, A. P.; Zhizhin, K. Y.; Miltsov, S. A.; Kuznetsov, N. T.; Kukushkin, V. Y. Organometallics 2012, 31, 1716− 1724. (16) Ostrovskii, V. A.; Trifonov, R. E.; Popova, E. A. Russ. Chem. Bull. 2012, 61, 768−780. (17) Gálvez-Ruiz, J. C.; Holl, G.; Karaghiosoff, K.; Klapötke, T. M.; Löhnwitz, K.; Mayer, P.; Nöth, H.; Polborn, K.; Rohbogner, C. J.; Suter, M.; Weigand, J. J. Inorg. Chem. 2005, 44, 4237−4253. (18) Xue, H.; Twamley, B.; Shreeve, J. M. J. Mater. Chem. 2005, 15, 3459−3465. (19) Aridoss, G.; Laali, K. K. Eur. J. Org. Chem. 2011, 6343−6355. (20) Gavazov, K. B.; Dimitrov, A. N.; Lekova, V. D. Russ. Chem. Rev. 2007, 76, 169−179. (21) Dhayabaran, V. V.; Lydia, I. S.; Merlin, J. P.; Srirenganayaki, P. Ionics 2004, 10, 123−125. (22) Gaponik, P. N.; Voitekhovich, S. V.; Ivashkevich, O. A. Russ. Chem. Rev. 2006, 75, 507−539. (23) Roh, J.; Vávrová, K.; Hrabálek, A. Eur. J. Org. Chem. 2012, 6101−6118. (24) Bräse, S.; Gil, C.; Knepper, K.; Zimmermann, V. Angew. Chem. 2005, 44, 5188−5240. (25) Wittenberger, S. J. Org. Prep. Proced. Int. 1994, 26, 499−531. (26) Demko, Z. P.; Sharpless, K. B. J. Org. Chem. 2001, 66, 7945− 7950. (27) Popova, E. A.; Trifonov, R. E.; Ostrovskii, V. A. ARKIVOC 2012, 45−65. (28) Popova, E. A.; Bokach, N. A.; Haukka, M.; Trifonov, R. E.; Ostrovskii, V. A. Inorg. Chim. Acta 2011, 375, 242−247. (29) Durham, J. L.; Tirado, J. N.; Knott, S. A.; Oh, M. K.; McDonald, R.; Szczepura, L. F. Inorg. Chem. 2012, 51, 7825−7836. (30) Mahmoudi, A.; Dehghanpour, S.; Gholamrezazadeh, C.; Jahanbakhshyan, M.; Mahmoudkhani, A. H.; Attari, N. Polyhedron 2012, 42, 265−270. (31) Szczepura, L. F.; Oh, M. K.; Knott, S. A. Chem. Commun. 2007, 8, 4617−4619. (32) Mukhopadhyay, S.; Mukhopadhyay, B. G.; Guedes da Silva, M. F. C.; Lasri, J.; Charmier, M. A. J.; Pombeiro, A. J. L. Inorg. Chem. 2008, 47, 11334−13341. (33) Lasri, J.; Guedes da Silva, M. F. C.; Kopylovich, M. N.; Ghosh Mukhopadhyay, B.; Pombeiro, A. J. L. Eur. J. Inorg. Chem. 2009, 2009, 5541−5549. (34) Liu, F.-C.; Lin, Y.-L.; Yang, P.-S.; Lee, G.-H.; Peng, S.-M. Organometallics 2010, 29, 4282−4290. (35) Klapötke, T. M.; Krumm, B.; Moll, R. Eur. J. Inorg. Chem. 2011, 2011, 422−428. (36) Quast, H.; Bieber, L.; Meichsner, G. Liebigs Ann. Chem. 1987, 469−475. (37) Amer, M. I. K.; Booth, B. L. J. Chem. Res., Synop. 1993, 4−5. (38) Hanessian, S.; Simard, D.; Deschênes-Simard, B.; Chenel, C.; Haak, E. Org. Lett. 2008, 10, 1381−1384. (39) Kumar, A.; Narayanan, R.; Shechter, H. Inorg. Chem. 1996, 61, 4462−4465. (40) Finnegan, W. G.; Henry, R. A.; Lofqui, R. J. Am. Chem. Soc. 1958, 80, 3908−3911. (41) Yaouanc, J. J.; Sturtz, G.; Kraus, J. L.; Chastel, C.; Colin, J. Tetrahedron Lett. 1980, 21, 2689−2692. (42) Demko, Z. P.; Sharpless, K. B. Angew. Chem. 2002, 41, 2110− 2113.

ASSOCIATED CONTENT

S Supporting Information *

Computational details, physicochemical data of sodium salts 3a−d, 1H, 13C{1H}, and 11B{1H} NMR spectra, tables with the crystal data and structure refinements, calculated total energies, enthalpies, Gibbs free energies, entropies, and Cartesian atomic coordinates of the equilibrium structures. This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*Fax: +7 812 4286939. Tel: +7 812 4286890. E-mail: bokach@ nb17701.spb.edu. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Russian Fund for Basic Research (grants 12-0333071 and 11-03-00262) and Saint Petersburg State University for research grants (12.39.1050.2012 and 12.38.781.2013). A.L.M. expresses his gratitude to the Government of Saint Petersburg for a grant for graduate and undergraduate students (2012). M.L.K. thanks Fundaçaõ para a Ciência e a Tecnologia (FCT), Portugal, for the financial support (projects PEst-OE/ QUI/UI0100/2013, PTDC/QUI-QUI/119561/2010, grant SFRH/BPD/88473/2012) and FCT and IST for the contract within the “FCT Investigator” program. We acknowledge the Center for Magnetic Resonance and the X-ray Diffraction Centre of Saint Petersburg State University for performing the NMR and XRD studies and the Computer Center (at Petrodvorets) of Saint Petersburg State University for providing their computer facilities for the theoretical calculations.

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REFERENCES

(1) Sivaev, I. B.; Votinova, N. A.; Bragin, V. I.; Starikova, Z. A.; Goeva, L. V.; Bregadze, V. I.; Sjoberg, S. J. Organomet. Chem. 2002, 657, 163−170. (2) Ringstrand, B.; Kaszynski, P.; Young, V. G.; Janou, Z. Inorg. Chem. 2010, 1166−1179. (3) Polyakova, I. N.; Zhizhin, K. Y.; Kuznetsov, N. T. Crystallogr. Rep. 2007, 52, 271−274. (4) Froehner, G.; Challis, K.; Gagnon, K.; Getman, T.; Luck, R. Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 2006, 36, 777−785. (5) Sícha, V.; Plesek, J.; Kvícalová, M.; Císarová, I.; Grüner, B. Dalton Trans. 2009, 851−860. (6) Zhdanov, A. P.; Lisovsky, M. V.; Goeva, L. V.; Razgonyaeva, G. A.; Polyakova, I. N.; Zhizhin, K. Y.; Kuznetsov, N. T. Russ. Chem. Bull. 2009, 58, 1694−1700. (7) Zhdanov, A. P.; Polyakova, I. N.; Razgonyaeva, G. A.; Zhizhin, K. Y.; Kuznetsov, N. T. Russ. J. Inorg. Chem. 2011, 56, 847−855. (8) Mindich, A. L.; Bokach, N. A.; Kuznetsov, M. L.; Haukka, M.; Zhdanov, A. P.; Zhizhin, K. Y.; Miltsov, S. A.; Kuznetsov, N. T.; Kukushkin, V. Y. ChemPlusChem 2012, 77, 1075−1086. (9) Bokach, N. A.; Kuznetsov, M. L.; Kukushkin, V. Y. Coord. Chem. Rev. 2011, 255, 2946−2967. (10) Kritchenkov, A. S.; Bokach, N. A.; Starova, G. L.; Kukushkin, V. Y. Inorg. Chem. 2012, 51, 11971−11979. 6585


Organometallics

Article

(78) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (79) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241. (80) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Buran, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision C.01; Gaussian, Inc.: Wallingford, CT, 2009. (81) Kuznetsov, M. L.; Kukushkin, V. Y.; Dement’ev, A. I.; Pombeiro, A. J. L. J. Phys. Chem. A 2003, 107, 6108−6120. (82) Kuznetsov, M. L.; Kukushkin, V. Y. J. Org. Chem. 2006, 71, 582−592. (83) Kuznetsov, M. L.; Nazarov, A. A.; Kozlova, L. V; Kukushkin, V. Y. J. Org. Chem. 2007, 72, 4475−4485. (84) Burns, L. A.; Vázquez-Mayagoitia, Á .; Sumpter, B. G.; Sherrill, C. D. J. Chem. Phys. 2011, 134, 084107. (85) Sumimoto, M.; Kawashima, Y.; Yokogawa, D.; Hori, K. Int. J. Quantum Chem. 2013, 113, 272−276. (86) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1991, 95, 5853− 5860. (87) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154− 2161. (88) Gonzalez, C.; Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523− 5527. (89) Hratchian, H. P.; Schlegel, H. B. J. Chem. Theory Comput. 2005, 1, 61−69. (90) Tomasi, J.; Persico, M. Chem. Rev. 1994, 94, 2027−2094. (91) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995−2001. (92) Wertz, D. H. J. Am. Chem. Soc. 1980, 102, 5316−5322. (93) Cooper, J.; Ziegler, T. Inorg. Chem. 2002, 41, 5019−5026. (94) Wiberg, B. Tetrahedron 1967, 24, 1083−1096. (95) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899−926. (96) Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Oxford Univ. Press: Oxford, 1990. (97) Keith, T. A. AIMAll (Version 13.01.27); TK Gristmill Software: Overland Park, KS, USA, 2013 (aim.tkgristmill.com).

(43) Demko, Z. P.; Sharpless, K. B. Angew. Chem. 2002, 41, 2113− 2116. (44) Aldhoun, M.; Massi, A.; Dondoni, A. J. Org. Chem. 2008, 73, 9565−9575. (45) Tu, X.; Boroson, E.; Truong, H.; Muñoz-Castro, A.; ArratiaPérez, R.; Nichol, G. S.; Zheng, Z. Inorg. Chem. 2010, 49, 380−382. (46) Tu, X.; Truong, H.; Alster, E.; Muñoz-Castro, A.; Arratia-Pérez, R.; Nichol, G. S.; Zheng, Z. Chem.Eur. J. 2011, 17, 580−587. (47) Geary, W. J. Coord. Chem. Rev. 1971, 7, 81−122. (48) Mindich, A. L.; Pavlishchuk, A. V.; Bokach, N. A.; Starova, G. L.; Zhizhin, K. Y. Acta Crystallogr. Sect. E 2012, 68, o3284−o3285. (49) Dou, D.; Mavunkal, I. J.; Bauer, J. A. K.; Knobler, C. B.; Hawthorne, M. F.; Shore, S. G. Inorg. Chem. 1994, 33, 6432−6434. (50) Yanai, H.; Sakiyama, T.; Oguchi, T.; Taguchi, T. Tetrahedron Lett. 2012, 53, 3161−3164. (51) Paul, A.; Einsiedel, J.; Waibel, R.; Heinemann, F. W.; Meyer, K.; Gmeiner, P. Tetrahedron 2009, 65, 6156−6168. (52) Gleiter, R.; Baumegger, A.; Freeman, R.; Schuck, R.; Schrank, F.; Centre, D.; Road, L. Angew. Chem. 1990, 102, 724−726. (53) Berionni, G.; Branca, M.; Pégot, B.; Marrot, J.; Kizilian, E.; Goumont, R. Eur. J. Org. Chem. 2011, 2011, 5104−5113. (54) Gaponik, P. N.; Voitekhovich, S. V.; Ivashkevich, O. A.; Lyakhov, A. S.; Govorova, A. A. Chem. Heterocycl. Compd. 1998, 34, 579−586. (55) Araki, S.; Yokoi, K.; Sato, R. J. Heterocycl. Chem. 2009, 46, 164− 171. (56) Moyano, A.; Pericàs, M. A.; Valentí, E. J. Org. Chem. 1989, 54, 573−582. (57) Lecea, B.; Adeta, A.; Rea, G.; Ugalde, J. M.; Cossfo, F. P.; Toma, D. J. Am. Chem. Soc. 1994, 116, 9613−9619. (58) Morao, I.; Lecea, B.; Cossío, F. P. J. Org. Chem. 1997, 62, 7033− 7036. (59) Cossio, F. P.; Morao, I.; Jiao, H.; von Rague Schleyer, P. J. Am. Chem. Soc. 1999, 121, 6737−6746. (60) Cantillo, D.; Gutmann, B.; Kappe, C. O. J. Org. Chem. 2012, 77, 10882−10890. (61) Cantillo, D.; Gutmann, B.; Kappe, C. O. J. Am. Chem. Soc. 2011, 133, 4465−4475. (62) Himo, F.; Demko, Z. P.; Noodleman, L. J. Org. Chem. 2003, 68, 9076−9080. (63) Himo, F.; Demko, Z. P.; Noodleman, L.; Sharpless, K. B. J. Am. Chem. Soc. 2003, 125, 9983−9987. (64) Himo, F.; Demko, Z. P.; Noodleman, L.; Sharpless, K. B. J. Am. Chem. Soc. 2002, 124, 12210−12216. (65) Jursic, B. S.; Zdravkovski, Z. J. Mol. Struct. (THEOCHEM) 1997, 389, 69−74. (66) Kritchenkov, A. S.; Bokach, N. A.; Kuznetsov, M. L.; Dolgushin, F. M.; Tung, T. Q.; Molchanov, A. P.; Kukushkin, V. Y. Organometallics 2012, 31, 687−699. (67) Yu, Y.; Fujita, H.; Ohno, M.; Eguchi, S. Synthesis 1995, 498− 500. (68) Yu, Y.; Watanabe, N.; Ohno, M.; Eguchi, S. J. Chem. Soc., Perkin Trans. 1 1995, 1417−1421. (69) Yu, Y.; Ohno, M.; Eguchi, S. J. Chem. Soc., Chem. Commun. 1994, 331−332. (70) Zhizhin, K. Y.; Mustyatsa, V. N.; Matveev, E. Y.; Drozdova, V. V.; Votinova, N. A.; Polyakova, I. N.; Kuznetsov, N. T. Russ. J. Inorg. Chem. 2003, 48, 671−675. (71) Kukushkin, V. Y.; Moiseev, A. I. Inorg. Chim. Acta 1990, 176, 79−81. (72) Martinsen, A.; Songstad, J. Acta Chem. Scand. A 1977, 31, 645− 650. (73) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (74) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341. (75) CrysAlisPro, Version 1.171.36.20 (release 27-06-2012); Agilent Technologies, 2012. (76) Clark, R. C.; Reid, J. S. Acta Crystallogr. 1995, A51, 887−897. (77) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. 6586


Borylated Tetrazoles from Cycloaddition of Azide Anions to Nitrilium

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