Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO Wits, Johannesburg, 2050 South Africa.
Inorg Chem. 2011 Sep 19;50(18):8700-18. doi: 10.1021/ic200285k. Epub 2011 Aug 18.
A stable yellow derivative of cobyrinic acid heptamethyl ester, (5R,6R)-Coα,Coβ-dicyano-5,6-dihydro-5-hydroxy-heptamethylcob(III)yrinate-c,6-lactone (DCSYCbs), was prepared from dicyanocobyrinic acid heptamethyl ester (DCCbs). The C5 carbon is oxidized and the c side chain cyclized to form a lactone at C6; the 13 atom, 14 π-e(-) delocalized system of corrins is interrupted, giving a triazamethine system with four conjugated double bonds between N22 and N24 and an isolated double bond between N21 and C4. Stable yellow aquacyanocobyrinic acid heptamethyl ester (ACSYCbs) was prepared by driving off HCN with N(2) in a methanol/acetic acid solution. The electronic spectra of DCCbs and DCSYCbs appear similar except that the bands in DCSYCbs are shifted to shorter wavelengths and the γ-band is much less intense. The experimental spectra were adequately modeled using TD-DFT at the PBE1PBE/6-311G(d,p) level of theory. DCSYCbs crystallizes in the space group P2(1)2(1)2(1) (R(1) = 6.08%) with Z = 4, including one methanol solvent molecule and one water molecule per cobester. The addition of a hydroxyl group at C5 causes loss of the double bond between C5 and C6 and elongation of the C5-C6 bond. From a combination of two-dimensional (1)H TOCSY and ROESY NMR spectra and (1)H/(13)C HSQC and HMBC data, the complete (1)H and (13)C NMR assignments of DCSYCbs were possible, except for two of the ester methyl groups and the (13)C resonances of the two axial cyanide ligands. The latter were assigned using relative chemical shifts calculated by GIAO-DFT methods. The (59)Co resonance of DCCbs was observed at 4074 ppm while that of DCSYCbs is shifted downfield to 4298 ppm. Comparison with available (59)Co data of analogous systems suggests that the more π-conjugated corrin of DCCbs interacts more strongly with the metal than the less extensively conjugated macrocycle of DCSYCbs. As the strength of the interaction between Co(III) and an equatorial macrocycle increases, ν(CN) of axially coordinated CN(-) shifts to lower frequency; in DCSYCbs and DCCbs ν(CN) occurs at 2138 and 2123 cm(-1), respectively. Hence the corrin ligand in DCCbs interacts more strongly with the metal than the stable yellow corrin ligand, with its diminished conjugation. The UV-vis spectral data and DFT-calculated MOs are consistent with greater overlap between the corrin and the metal orbitals in DCCbs relative to DCSYCbs, which gives the metal in the former a softer, more covalent character.
一种稳定的黄色 cobyrinic 酸庚甲酯衍生物，（5R，6R）-Coα，Coβ-二氰基-5，6-二氢-5-羟基-庚基（III）yrinate-c，6-内酯（DCSYCbs），由二氰基 cobyrinic 酸庚甲酯（DCCbs）制备。C5 碳原子被氧化，c 侧链在 C6 处环化形成内酯; corrin 的 13 原子，14π-e（-）离域系统被中断，在 N22 和 N24 之间形成四共轭双键的三嗪甲脒系统和 N21 和 C4 之间的孤立双键。在甲醇/乙酸溶液中用 N(2)逐出 HCN 制备稳定的黄色水合氰基 cobyrinic 酸庚甲酯（ACSYCbs）。DCCbs 和 DCSYCbs 的电子光谱除了 DCSYCbs 的带移向较短的波长并且γ带的强度大大降低之外看起来相似。实验光谱在 PBE1PBE/6-311G（d，p）理论水平上使用 TD-DFT 进行了充分的建模。DCSYCbs 在空间群 P2(1)2(1)2(1)（R(1) = 6.08%）中结晶，每个 cobester 包含一个甲醇溶剂分子和一个水分子。C5 上羟基的添加导致 C5 和 C6 之间的双键丢失并且 C5-C6 键伸长。从二维（1）H TOCSY 和 ROESY NMR 光谱以及（1）H/（13）C HSQC 和 HMBC 数据的组合，DCSYCbs 的完整（1）H 和（13）C NMR 分配是可能的，除了两个酯基甲基和两个轴向氰化物配体的（13）C 共振。后两者使用通过 GIAO-DFT 方法计算的相对化学位移进行了分配。DCCbs 的（59）Co 共振在 4074 ppm 处观察到，而 DCSYCbs 的共振移向更高场至 4298 ppm。与类似系统的可用（59）Co 数据的比较表明，DCCbs 的更具π-共轭的 corrin 与金属的相互作用比 DCSYCbs 的不太广泛共轭的大环更强。随着 Co（III）与赤道大环之间的相互作用强度增加，轴向配位的 CN（-）的ν（CN）移向更低的频率; 在 DCSYCbs 和 DCCbs 中，ν（CN）分别发生在 2138 和 2123 cm（-1）处。因此，DCCbs 中的 corrin 配体与金属的相互作用比稳定的黄色 corrin 配体更强，其共轭度降低。UV-vis 光谱数据和 DFT 计算的 MO 与 DCCbs 中 corrin 和金属轨道之间的更大重叠一致，这使得前者中的金属具有更软，更共价的特性。
