亚洲免费av电影一区二区三区,日韩爱爱视频,51精品视频一区二区三区,91视频爱爱,日韩欧美在线播放视频,中文字幕少妇AV,亚洲电影中文字幕,久久久久亚洲av成人网址,久久综合视频网站,国产在线不卡免费播放

        ?

        How long a C-C bond can be? An example of extraordinary long C-C single bond in 1,2-diarylamino-o-carborane

        2019-09-28 05:36:48YileWuJieZhangZuoweiXie
        Chinese Chemical Letters 2019年8期

        Yile Wu,Jie Zhang,Zuowei Xie*

        Department of Chemistry and State Key Laboratory of Synthetic Chemistry,The Chinese University of Hong Kong,Hong Kong,China

        Keywords:

        o-Carborane

        C-C single bond

        Hyperconjugation

        Amine

        X-ray structure

        ABSTRACT

        How long a C—C bond can be?A question has long fascinated chemists.This work reports an example of extraordinary long C—C bond distance of 1.990(4) ? observed in single-crystal X-ray structure of 1,2-(NHMes)2-o-carborane(2;Mes=2,4,6-trimethylphenyl).DFTcalculations show that hyperconjugation of lone pairs of the nitrogen atoms into the empty s*orbital of the cage C—C bond is the origin of the bond elongation.Such hyperconjugation can be suppressed if the two nitrogen atoms in 2 are linked to a Lewis acidic germanium (II) center.

        The C—C bonds are the basic building blocks in organic compounds and the carbon-based living things.Generally,the normal Csp3—Csp3bond length in organic compounds is about 1.54 ?[1].However,C—C single bonds with deviant bond lengths have received much attention over the years [2-4].The linear relationship between C—C bond length and the bond dissociation energies (BDE) reveals that the deviation of C—C bond lengths from the standard will cause significant changes in BDE [5].Recently,substantial progress has been made in synthesizing compounds with elongated C—C bond lengths (Fig.1).For example,hexaphenylethane (HPE) derivative A,reported by Mislow et al.,features a long C—C bond length of 1.67(3) ? [6].Other HPE derivatives B[7,8]and C[9],prepared by the Toda and Herges groups,are proved to be stable compounds with long C—C bond lengths of 1.734(5)? and 1.713(2)?,respectively.Beyond HPE derivatives,Schreiner et al.demonstrated that the caged-alkane dimer D,with a C—C bond length elongated to 1.704(4) ?,is stabilized by attractive dispersion interactions[10].Very recently,Suzuki et al.reported a series of dihydropyracylene with two spiro(dibenzocycloheptatriene) E having ultra-long C—C single bonds up to 1.806(2) ? in length [11].

        For 1,2-disubstituted o-carboranes [12],previous reports suggest a possibility of elongating the cage C—C bonds by replacing the substituents on the cage carbon atoms[13,14].Both experimental[15,16]and theoretical [17]results revealed that the aminosubstituting groups significantly elongated the corresponding cage C—C bonds due to the p-electron back-donation from the nitrogen lone pairs to the CC cage antibonding orbital.Especially,1,2-(NH2)2-1,2-C2B10H10was predicted by DFTcalculations to have longer C—C bonds than its-SH,OH,CH3and PH2derivatives[17].However,the known method for synthesizing bisamino-o-carboranes was not known till very recently[18],and only mono-amino-substituted ocarboranes have been reported [19].As an on-going project,we strivetocontinuewithoureffectsindevelopingnewmethodologies for efficient functionalization of o-carborane [19-22].We report herein a novel one-pot synthesis of 1,2-bis(arylamino)-o-carborane that features the ultra long C—C single bond distance of 1.990(4)?.Whilethispaperwasunderpreparation,thesynthesisandstructure of 1,2-(NH2)2-o-carborane and its derivatives were reported[18].

        Inspired by the synthesis of arylamines from the reaction of aryl Grignard reagents with nitrosoarenes [23],we hypothesized the preparation of 1,2-bis(arylamino)-o-carboranes directly from ocarboranes via a one-pot addition-reduction process.Hence,we started our investigation by reaction of 1,2-(MgCl)2-o-C2B10H10[24]with PhNO in THF,followed by treatment with LiBH4and FeCl2,respectively.The desired product 1,2-(phenylamino)2-o-C2B10H101 was isolated,after workup,in 26%yield.Replacement of 1,2-(MgCl)2-o-C2B10H10with 1,2-dilitho-o-carborane resulted in the isolation of 1 in 68% yield (Scheme 1).

        Under the same manner,1,2-(NHMes)2-o-carborane (2,Mes=2,4,6-trimethylphenyl) was prepared in 58% yield (see the Supporting information for detail) (Scheme 1).

        Fig.1.Reported compounds with elongated C—C bonds.

        Scheme 1.One-pot preparation of 1,2-bis(arylamino)-o-carboranes.

        Fig.2.Molecular structures of 1 and 2 with the anisotropic displacement parameters depicted at the 30% and the 50% probability level,respectively.The H atoms are omitted for clarity.

        Both 1 and 2 were characterized by1H,13C and11B NMR spectroscopy as well as HRMS.Their molecular structures are confirmed by single-crystal X-ray analyses (Fig.2).Their key structure parameters together with other know analogues are compiled in Table 1.The most interesting structural feature is the especially long cage C—C bonds,1.922(5)? in 1 and 1.990(4)? in 2.The latter is even longer than that of 1.931(2) ? observed in 1,2-(MesCH2NH)2-o-C2B10H10(F in Fig.1)[18].The average cage C-N bond distances of 1.380(4)? in 1 and 1.388(3)? in 2 are very close to that of 1.383(2)? in F.The average B—B distances of 1.777 ? in 2,1.774 ? in 3 and 1.777 ? in F are very comparable to each other.

        Table 1 Key structural parameters for o-carborane,2,3 and F.

        Scheme 2.Illustration of the hyperconjugation.

        To gain more insight into the electronic structure of 2,DFT calculations were carried out for the structural optimization of ocarborane and 2 at the B3LYP/6-31G**level of theory[17].Natural bond orbital(NBO) analyses(B3LYP/6-311G++**) indicate that the Wiberg bond index (WBI) of the cage C—C bond in 2 (0.33) is significantly smaller than that in o-carborane(0.74),and is slightly smaller than that in F(0.34,Table 1).On the other hand,the WBI of 1.10 for Ccage-N bond in 2 suggests its multiple bonding characters.For the two nitrogen atoms in 2,the occupancies of long pairs(LPs)drop to a low value of 1.81e.Meanwhile,the empty s*C—C orbital occupancy of 2 is calculated to be 0.44e,which is significantly larger than that of 0.07e in o-carborane,indicating an electron transfer from the N atom to the empty s*cage C—C orbital.These results are in line with the literature reports[17,18],implying that the origin of the elongated cage C—C bonds in 1 and 2 results from the hyperconjugation between the LPs of the nitrogen atoms and the empty s* C—C orbital,as illustrated in Scheme 2.

        Furthermore,the Ccage-Ccage-N-Caryltorsion angles of 116.4(2)°in 2 are closer to an ideal torsion angel of 120°required to establish the parallelism between the LP orbital of nitrogen and s* C—C orbital.In contrast,such torsion angles in 1 [83.9(4) to 87.9(4)°]and F[108.1(2)and 96.0(2)°](Table 1)are largely off the ideal one.These results reveal that the observed parallelism between LP orbital of nitrogen and s* C—C orbital in 2 enhances the hyperconjugation,leading to an extraordinary long C—C bond.

        It is clear that the lengthening of the cage C—C bond is closely related to the hyperconjugation aforementioned.We anticipated that such hyperconjugation would be suppressed if both N atoms in 2 are bonded to a strong Lewis acidic center.In this connection,treatment of 2 with 2 equivalent of n-BuLi in toluene,followed by the addition of 1 equiv.of GeCl2·dioxane,gave a germylene 3 in 81%yield (Scheme 3).Compound 3 was fully characterized by1H,13C,11B NMR and HRMS as well as single-crystal X-ray analysis.

        Scheme 3.Synthesis and structure of germylene 3.The anisotropic displacement parameter is depicted at the 50% probability level.The H atoms are omitted for clarity.

        The cage C—C bond distance of 1.637(3)? in 3 is close to that of 1.624(8)? in o-carborane,but is significantly shorter than that of 1.990(4)? observed in 2(Table 1).Accordingly,the Ccage-N bond distance of 1.414(3)? in 3 is much longer than that of 1.388(3)? in 2.NBO analyses(at the B3LYP/6-311G++**level of theory)predict a WBI of 0.75 for the cage C—C bond in 3,which is very similar to that of 0.74 in o-carborane (Table 1).On the other hand,a WBI of 1.03 for the Ccage-N bond in 3 is considerably smaller than that of 1.10 in 2.These results suggest that no hyperconjugation is observed between LPs of the nitrogen atoms and the s*orbital of the cage C—C bond in 3.Instead,the nitrogen atoms donate their LPs to the empty p-orbital of the Ge(II)center in 3,stabilizing such a germylene compound [26].

        In summary,we describe a new one-pot synthesis of 1,2-bis(arylamino)-o-carboranes 1 and 2,by treatment of 1,2-dilithio-ocarborane with nitrosoarenes.Single-crystal X-ray analyses reveal that 1 and 2 have extraordinary long cage C—C bonds with distances of 1.922(5) ? and 1.990(4) ?,respectively.On the other hand,a WBI of 1.10 for Ccage-N in 2 suggests its multiple bonding characters.DFT calculations on 2 indicate that the hyperconjugation between the LPs of nitrogen atoms and the empty s* C—C orbital is responsible for the elongated C—C bonds in 1 and 2.

        How long a C—C bond can be? Though this is still an open question,the current work pushes the limit further out.

        Acknowledgments

        This work was supported by a grant from the Research Grants Council of the Hong Kong Special Administration Region(No.14305918).

        Appendix A.Supplementary data

        Supplementarymaterialrelatedtothisarticlecanbefound,inthe online version,at doi:https://doi.org/10.1016/j.cclet.2019.04.034.

        亚洲视频在线观看一区二区三区| 久久精品国产99精品九九| 免费一级黄色大片久久久| 视频一区中文字幕在线观看| 亚洲黄色天堂网站在线观看禁18 | 一区二区三区四区亚洲免费| 欧美日韩精品一区二区视频| 亚洲国产精品特色大片观看完整版| 日产精品一区二区三区| 亚洲一区久久蜜臀av| 中文人妻av久久人妻水蜜桃| 欧美最猛黑人xxxx黑人表情| 骚片av蜜桃精品一区| 中文字幕乱码人妻在线| 亚洲成av人在线观看网址| 躁躁躁日日躁| 99在线无码精品秘 人口| 高清少妇二区三区视频在线观看| 亚洲色中文字幕无码av| 韩国19禁主播深夜福利视频| 国产美女三级视频网站| 精品国产中文字幕久久久| 我爱我色成人网| 精品国产香蕉伊思人在线又爽又黄| 久久精品中文字幕免费| 国产亚洲av另类一区二区三区| 男人靠女人免费视频网站| 久久精品亚洲中文无东京热| 在线久草视频免费播放| 无码人妻精品一区二区三区夜夜嗨| 亚洲av日韩av无码av| 大白屁股流白浆一区二区三区 | 高h小月被几个老头调教| 久久精品国产亚洲精品| 欧美亚洲日韩国产人成在线播放| 国内自拍偷拍亚洲天堂| 草青青视频手机免费观看| 国产亚洲成av人片在线观黄桃| 欧美情侣性视频| 久久亚洲精品国产精品婷婷| 亚洲中文字幕久久精品品|