Grapperhaus Craig A., Tuntulani Thawatchai, Reibenspies Joseph H., Darensbourg Marcetta Y.
Department of Chemistry, Texas A&M University, College Station, Texas 77843.
Inorg Chem. 1998 Aug 10;37(16):4052-4058. doi: 10.1021/ic971599f.
The dimeric dithiolate complex [1,5-bis(mercaptoethyl)-1,5-diazacyclooctanato]zinc(II), (bme-daco)Zn or Zn-1, and its cadmium analogue, Cd-1, were investigated as models for the active site of zinc-dependent methylation proteins. The key issue addressed was whether alkylation of a thiolate in a relatively rigid tetradentate ligand would result in coordination of the thioether product to the metal. On the basis of (1)H and (13)C NMR spectroscopy and similar reactivity toward alkylating agents, the newly synthesized cadmium complex, Cd-1, is proposed to be isostructural with the previously reported Zn-1 complex, which is known from X-ray crystallography to be dimeric in the solid state (Tuntulani, T.; Reibenspies, J. H.; Farmer, P. J.; Darensbourg, M. Y. Inorg. Chem.1992, 31, 3497). Iodomethane reacts with Zn-1 in hot CH(3)OH/CH(3)CN to produce a thioether which dissociates, replaced by coordination of iodide in the pseudotetrahedral complex, (Me(2)bme-daco)ZnI(2) or Zn-2. Complex Zn-2 crystallizes in the triclinic P&onemacr; space group with a = 7.911(2) Å, b = 10.675(2) Å, c = 12.394(2) Å, alpha = 75.270(10) degrees, beta = 75.270(10) degrees, gamma = 82.12(2) degrees, V = 998.270 Å(3), and Z = 2. An analogous reaction was observed for the cadmium derivative, Cd-1, which displays a (1)H NMR spectrum identical to that of Zn-2. In attempts to promote thioether binding, the iodide was displaced by addition of AgBF(4) to solutions of Zn-2 or the BF(4)(-) analogue was synthesized directly from Zn(BF(4))(2) and methylated ligand, Me(2)bme-daco, to yield Zn-3. Similar reactions with the cadmium analogue yielded a product identified as Cd-3 that was indistinguishable from Zn-3 by (1)H NMR. The (113)Cd NMR spectra of Cd-3 displayed a single resonance at 88 ppm consistent with a hard donor environment and inconsistent with sulfur binding. As a further attempt to induce thioether binding to zinc, the macrocyclization reagent 1,3-dibromopropane was added to Zn-1. The resulting product, BrZn(macrocycle), was only slightly soluble in pyridine and identified by +FAB/MS as the desired macrocyclic product with a large amount of free macrocycle ligand. Recrystallization from pyridine/ether resulted in loss of the zinc as Zn(py)(2)Br(2), which was obtained as colorless crystals and characterized by X-ray crystallography. Complex Zn(py)(2)Br(2) crystallizes in the monoclinic P2(1)/c space group with a = 8.534(2) Å, b = 18.316(4) Å, c = 8.461(2) Å, beta = 101.07(3) degrees, V = 1297.9(5) Å(3), and Z = 4.
二聚二硫醇盐配合物[1,5-双(巯基乙基)-1,5-二氮杂环辛烷]锌(II)，即(bme-daco)Zn或Zn-1，及其镉类似物Cd-1，作为锌依赖性甲基化蛋白活性位点的模型进行了研究。所解决的关键问题是，在相对刚性的四齿配体中硫醇盐的烷基化是否会导致硫醚产物与金属配位。基于(1)H和(13)C核磁共振光谱以及对烷基化试剂的类似反应性，新合成的镉配合物Cd-1被认为与先前报道的Zn-1配合物同构，从X射线晶体学可知Zn-1在固态时为二聚体(Tuntulani, T.; Reibenspies, J. H.; Farmer, P. J.; Darensbourg, M. Y. Inorg. Chem.1992, 31, 3497)。碘甲烷在热的CH(3)OH/CH(3)CN中与Zn-1反应生成一种硫醚，该硫醚会解离，被伪四面体配合物(Me(2)bme-daco)ZnI(2)或Zn-2中的碘离子配位取代。配合物Zn-2在三斜P&onemacr;空间群中结晶，a = 7.911(2) Å，b = 10.675(2) Å，c = 12.394(2) Å，α = 75.270(10)°，β = 75.270(10)°，γ = 82.12(2)°，V =
