Organic Materials Research Group, Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA.
Inorg Chem. 2010 Feb 1;49(3):1166-79. doi: 10.1021/ic9021323.
Amino acid closo-1-CB(9)H(8)-1-COO-10-NH(3) (4) was prepared by amination of iodo acid closo-1-CB(9)H(8)-1-COOH-10-I (1) with LiHMDS in a practical and reproducible manner. The apparent dissociation constants, pK(2) = 5.6 and pK(1) > 11, were measured for 4[NMe(4)] in 50% aq. EtOH. Diazotization of 4 with NO(+)PF(6)(-) under mildly basic conditions afforded stable dinitrogen acid [closo-1-CB(9)H(8)-1-COOH-10-N(2)] (5). Activation parameters (DeltaH(++) = 33.9 +/- 1.4 kcal mol(-1) and DeltaS(++) = 10 +/- 3.5 cal mol(-1) K(-1)) for thermolysis of its methyl ester [closo-1-CB(9)H(8)-1-COOMe-10-N(2)] (11) in PhCN were established, and the heterolysis of the B-N bond is believed to be the rate-determining step. Electrochemical analysis showed a partially reversible reduction process for 11 (E(1/2)(red) = -1.03 V) and 5(-) (E(1/2)(red) = -1.21 V), which are more cathodic than reduction of [closo-1-CB(9)H(9)-1-N(2)] (17). The dinitrogen acid 5 was reacted with pyridine and N,N-dimethylthioformamide, to form pyridine acid 6 and protected mercapto acid 7, respectively, through a boronium ylide intermediate 18. Compound 7 was converted to sulfonium acid 8. The molecular and crystal structures for 5 [C(2)H(9)B(9)N(2)O(2) monoclinic, P2(1)/n, a = 7.022(2) A, b = 11.389(4) A, c = 12.815(4) A, beta = 96.212(5) degrees ; V = 1018.8(6) A(3), Z = 4,], 6 [C(7)H(14)B(9)NO(2), monoclinic, P2(1)/n, a = 14.275(4) A, b = 12.184(3) A, c = 30.538(8) A, beta = 95.377(4) degrees ; V = 5288(3) A(3), Z = 16], and 8 [C(7)H(19)B(9)O(2)S, monoclinic, P2(1)/c, a = 15.988(5) A, b = 19.377(6) A, c = 9.655(3) A, beta = 98.348(5) degrees; V = 2959.4(16) A(3), Z = 8] were determined by X-ray crystallography and compared with results of density functional theory (DFT) and MP2 calculations. Electronic structures of 5, 6, and related species were elucidated with electronic spectroscopy and assessed computationally at the B3LYP/6-31G(d,p), MP2/6-31G(d,p), and ZINDO//MP2 levels of theory.
氨基酸 [闭式-1-CB(9)H(8)-1-COO-10-NH(3)]-（4）通过碘代酸 [闭式-1-CB(9)H(8)-1-COOH-10-I]-（1）与 LiHMDS 在实际和可重复的方式中的胺化制备。在 50%乙醇中的 4[NMe(4)]的表观离解常数，pK(2)=5.6 和 pK(1)>11，进行了测量。在温和碱性条件下用 NO(+)PF(6)(-)对 4 进行重氮化，得到稳定的二氮酸 [闭式-1-CB(9)H(8)-1-COOH-10-N(2)]（5）。其甲酯[闭式-1-CB(9)H(8)-1-COOMe-10-N(2)]（11）在 PhCN 中的热解的活化参数（DeltaH(++)=33.9 +/- 1.4 kcal mol(-1)和 DeltaS(++)=10 +/- 3.5 cal mol(-1) K(-1)）被建立，并且认为 B-N 键的异裂是速率决定步骤。电化学分析表明 11（E(1/2)(red)=-1.03 V）和 5(-)（E(1/2)(red)=-1.21 V）的部分可逆还原过程，它们比[闭式-1-CB(9)H(9)-1-N(2)]（17）的还原更负。二氮酸 5 与吡啶和 N，N-二甲基硫代甲酰胺反应，分别通过硼叶立德中间体 18 形成吡啶酸 6 和保护的巯基酸 7。化合物 7 转化为硫鎓酸 8。5[C(2)H(9)B(9)N(2)O(2)]的分子和晶体结构，单斜晶系，P2(1)/n，a=7.022(2)A，b=11.389(4)A，c=12.815(4)A，β=96.212(5)°；V=1018.8(6)A(3)，Z=4，]，6[C(7)H(14)B(9)NO(2)]，单斜晶系，P2(1)/n，a=14.275(4)A，b=12.184(3)A，c=30.538(8)A，β=95.377(4)°；V=5288(3)A(3)，Z=16]和 8[C(7)H(19)B(9)O(2)S]，单斜晶系，P2(1)/c，a=15.988(5)A，b=19.377(6)A，c=9.655(3)A，β=98.348(5)°；V=2959.4(16)A(3)，Z=8]通过 X 射线晶体学确定，并与密度泛函理论（DFT）和 MP2 计算的结果进行了比较。5、6 和相关物种的电子结构通过电子光谱学阐明，并在 B3LYP/6-31G(d,p)、MP2/6-31G(d,p)和 ZINDO//MP2 理论水平上进行了计算评估。
