Complexes in which sp Carbon Chains span two Metals

本项目的目标是合成线状杂化碳链跨越两个过渡金属片段的配合物，并对其化学性质和物理性质进行详细的研究。在很长的链长，这种材料与钻石和石墨，经典的三维和二维SP3和SP2杂化的聚合物碳同素异形体有很强的概念联系。它们也比具有有机端基的类似物稳定得多。人们将逐渐寻求基于这种构建块的更复杂的体系结构。在一种努力中，具有C32-C40链的络合物将成为目标，其中金属-金属距离将超过5 nm；那些具有C24-C28链的络合物很容易分离并稳定在140℃。在另一种努力中，CX链将通过两个柔性的SP3碳链进行空间保护，这两个碳链跨越每个末端的施主原子。当足够长时，它们采用手性双螺旋构象，很像家用电线的绝缘。这些物种的氧化还原性质将被研究；预计混合价自由基离子的稳定性将得到提高。涉及轮烷的空间屏蔽SP链的其他方法将被研究。在另一项工作中，将合成具有平行CX链的此类络合物的侧向阵列或“束”。这些可以被看作是多股分子导线。在另一项工作中，将制备定义良好的纵向延伸阵列，例如PtCxPtCxPtCxPt物种。将在末端的铂原子上引入“鳄鱼夹”，这样就可以测量单分子的电导率。与螯合双膦的反应可能会引入“扭结”，这可能会(在适当的条件下)还原消除PtC3xPT物种，或者允许氧化偶联到每个角落都包含铂原子的多边形。还将通过单铂物种的氧化偶联来制备多边形。将尝试挤压铂原子，生成环碳CX(一种单体碳同素异形体)。将研究C=C部分的反应，如三聚成六取代苯和间位生成奇碳物种M(C=C)n‘C=M’。在合作努力中，将表征每一类络合物的非线性光学性质和光物理性质。将特别注意定义链长效应和链-链相互作用。关于如何将这些线状不饱和分子设计成各种复杂的结构的详细知识将会产生。有了这个奖项，有机和高分子化学项目将支持德克萨斯农工大学化学系的约翰·A·格拉迪斯教授的研究。格拉迪斯教授和他的学生正在探索含有金属原子封端的延长碳链的分子的合成和性质。这些系统模仿了目前颇受关注的全碳系统。它们有望在分子线、非线性光学材料和其他更复杂的分子聚集体的设计和建造中显示出各种不寻常的潜在相关性质。参与这个项目的学生将有机会与德国的学生和专门从事分子材料表征的物理化学家合作。

The objective of this project is to synthesize complexes in which wire-like sp-hybridized carbon chains span two transition metal fragments, and to conduct detailed studies of their chemical and physical properties. At very long chain lengths, such materials bear a strong conceptual relationship to diamond and graphite, the classical three- and two-dimensional sp3 and sp2-hybridized polymeric carbon allotropes. They are also much more stable than analogs with organic endgroups. Progressively more complex architectures based upon such building blocks will be sought. In one effort, complexes with C32-C40 chains, in which the metal-metal distances would surpass 5 nm, will be targeted; those with C24-C28 chains are easily isolable and stable to 140 C. In another effort, the Cx chain will be sterically protected via two flexible sp3 carbon chains that span donor atoms on each terminus. When sufficiently long, these adopt chiral double helical conformations, much like the insulation about household electrical wire. The redox properties of such species will be studied; it is anticipated that the stabilities of mixed valence radical ions will be enhanced. Other approaches to sterically shielded sp chains involving rotaxanes will be investigated. In another effort, lateral arrays or "bundles" of such complexes with parallel Cx chains will be synthesized. These can be viewed as multi-stranded molecular wires. In another effort, well-defined longitudinally extended arrays, such as PtCxPtCxPtCxPt species, will be prepared. "Alligator clips" will be introduced on the terminal platinum atoms such that single-molecule conductivities can be measured. Reactions with chelating diphosphines may introduce "kinks" that might allow (under appropriate conditions) reductive eliminations to PtC3xPt species or oxidative couplings to polygons that contain platinum atoms at each corner. Polygons will also be prepared by oxidative couplings of monoplatinum species. Attempts will be made to extrude the platinum atoms, generating a cyclocarbon Cx (a monomeric carbon allotrope). Reactions of the C=C moieties will be investigated, such as trimerizations to hexasubstituted benzenes and metatheses to give odd-carbon species M(C=C)n'C=M'. In collaborative efforts, the NLO and photophysical properties of each family of complexes will be characterized. Particular attention will be given to defining chain length effects and chain-chain interactions. A detailed knowledge of how to engineer these wire-like unsaturated molecules into a variety of sophisticated architectures will result.With this award, the Organic and Macromolecular Chemistry Program is supporting the research of Professor John A. Gladysz, of the Department of Chemistry at Texas A&M University. Professor Gladysz and his students are exploring the synthesis and properties of molecules containing extended carbon chains capped by metal atoms. These systems mimic all-carbon systems of considerable current interest. They are expected to display a variety of unusual properties of potential relevance in the design and construction of molecular wires, nonlinear optical materials, and other more complex molecular aggregates. Students involved in this project will have the opportunity to collaborate with students in Germany and with physical chemists specializing in the characterization of molecular materials.