Isolation and Reduction of Sterically Encumbered Arylboron Dihalides: Novel Boranediyl Insertion into C-C -Bonds
详细信息 查看全文
- 作者：Warren J. Grigsby and Philip P. Power
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：August 28, 1996
- 年：1996
- 卷：118
- 期：34
- 页码：7981 - 7988
- 全文大小：228K
- 年卷期：v.118,no.34(August 28, 1996)
- ISSN：1520-5126
文摘
The synthesis and subsequent reduction of the arylborondihalides2,6-Mes2C6H3BX2 (X= Cl (1); Br (2))and2,6-Trip2C6H3BBr2(3) (Mes =2,4,6-Me3C6H2- and Trip =2,4,6-i-Pr3C6H2-) aredescribed. Treatment of 2with lithium metal in diethyl ether gave the novel lithium9-borafluorenyl compounds 4 and 5 (see Scheme 1)inwhich the boranediyl intermediate has inserted into ano-Me-ring C-C 
-bond to form a borafluorenylstructureincorporating boron in a delocalized five-membered ring.Boranediyl insertion into C-C -bonds, as distinctfromboranediyl induced rearrangements involving C=C cleavage indelocalized aromatic substrates, is unknown. Themain difference between the structures of these products is that5 is dimerized as a consequence of the reductioninthe number of solvating ethers. Reduction of 2 withKC8 led to the isolation of the 9-borafluorenyl "ate"compounds6 and 7. These products also result fromC-C bond insertion by boron as seen in 4 and 5.However, the delocalizationis not observed owing to the addition of hydrogen (presumably fromsolvent) to the borons affording borate salts.Reduction of 3 with 3 equiv of KC8furnishes the new "diborate" species 8. Thiscompound features a unique B-Bbonded dianionic structure with a long (1.83(2) Å) B-B bondwhich arises from the association of two borateradical anion fragments that have a 9-borafluorenyl structure similarto those described above. Compounds2-8were characterized by 1H, 13C,7Li, and 11B NMR spectroscopy and by X-raycrystallography. Crystal data at 130K with Cu K
(
= 1.54178 Å) radiation: 1,C12H12.5B0.5Br, a= 15.562(5) Å, b = 9.156(2) Å, c= 16.368(5) Å,
= 111.23(2)
, Z = 4, space groupC2/c, R = 0.060 for 1338(I > 2(I)) data. 3,C18H14.5B0.5Br, a= 11.001(2)Å, b = 12.194(2) Å, c = 25.473(5)Å, Z = 8, space group Pbcm, R =0.065 for 1876 (I > 2(I)) data.4, C32H45BLi2O2, a = 23.611(6) Å,b = 12.812(5) Å, c = 10.194(3) Å,Z = 4, space group Pbn21,R = 0.085 for 1212 (I >2(I)) data. 5,C48H70B2Li4O2,a = 14.398(3) Å, b = 17.739(4) Å,c = 19.885(4) Å, = 97.64(3),Z = 4, spacegroup P21/c, R = 0.120for 3125 (I > 2(I)) data.6, C32H44BKO2,a = 9.235(4) Å, b = 22.292(7) Å,c = 14.301(8)Å, = 100.51(4), Z = 4, space groupP21/n, R = 0.074 for2968 (I > 2(I)) data.7·C6H6,C33H35BK, a =10.867(4) Å, b = 12.197(5) Å, c =12.358(5) Å, = 108.28(3), =111.76(3), 
= 101.96(3), Z = 2,spacegroup P
, R = 0.044 for 3291(I > 2(I)) data.8·1.5Et2O·hexane,C152H224B4K4O3.5,a = 17.686(13) Å, b =17.659(5) Å, c = 23.568(10) Å, =104.41(4), Z = 2, space group Pc,R = 0.097 for 4672 (I >2(I)) data.
-bond to form a borafluorenylstructureincorporating boron in a delocalized five-membered ring.Boranediyl insertion into C-C -bonds, as distinctfromboranediyl induced rearrangements involving C=C cleavage indelocalized aromatic substrates, is unknown. Themain difference between the structures of these products is that5 is dimerized as a consequence of the reductioninthe number of solvating ethers. Reduction of 2 withKC8 led to the isolation of the 9-borafluorenyl "ate"compounds6 and 7. These products also result fromC-C bond insertion by boron as seen in 4 and 5.However, the delocalizationis not observed owing to the addition of hydrogen (presumably fromsolvent) to the borons affording borate salts.Reduction of 3 with 3 equiv of KC8furnishes the new "diborate" species 8. Thiscompound features a unique B-Bbonded dianionic structure with a long (1.83(2) Å) B-B bondwhich arises from the association of two borateradical anion fragments that have a 9-borafluorenyl structure similarto those described above. Compounds2-8were characterized by 1H, 13C,7Li, and 11B NMR spectroscopy and by X-raycrystallography. Crystal data at 130K with Cu K ( = 1.54178 Å) radiation: 1,C12H12.5B0.5Br, a= 15.562(5) Å, b = 9.156(2) Å, c= 16.368(5) Å, = 111.23(2), Z = 4, space groupC2/c, R = 0.060 for 1338(I > 2(I)) data. 3,C18H14.5B0.5Br, a= 11.001(2)Å, b = 12.194(2) Å, c = 25.473(5)Å, Z = 8, space group Pbcm, R =0.065 for 1876 (I > 2(I)) data.4, C32H45BLi2O2, a = 23.611(6) Å,b = 12.812(5) Å, c = 10.194(3) Å,Z = 4, space group Pbn21,R = 0.085 for 1212 (I >2(I)) data. 5,C48H70B2Li4O2,a = 14.398(3) Å, b = 17.739(4) Å,c = 19.885(4) Å, = 97.64(3),Z = 4, spacegroup P21/c, R = 0.120for 3125 (I > 2(I)) data.6, C32H44BKO2,a = 9.235(4) Å, b = 22.292(7) Å,c = 14.301(8)Å, = 100.51(4), Z = 4, space groupP21/n, R = 0.074 for2968 (I > 2(I)) data.7·C6H6,C33H35BK, a =10.867(4) Å, b = 12.197(5) Å, c =12.358(5) Å, = 108.28(3), =111.76(3), = 101.96(3), Z = 2,spacegroup P, R = 0.044 for 3291(I > 2(I)) data.8·1.5Et2O·hexane,C152H224B4K4O3.5,a = 17.686(13) Å, b =17.659(5) Å, c = 23.568(10) Å, =104.41(4), Z = 2, space group Pc,R = 0.097 for 4672 (I >2(I)) data.