A New Generation of All-Carbon Bridged Bimetallic Complexes featuring Redox-Active, Group 6 Metal End-Caps.

金属稳定的碳链[M-(CC)x-M]n+在过去的10年里引起了人们越来越多的兴趣，主要是因为随着化合物的形式氧化态的变化，电子结构发生了显著的变化。虽然这项工作的大部分都集中在同双金属的例子上，但最近的合成进展使异金属的例子变得容易获得。这是一个特别令人兴奋的发展，因为许多关于同金属多碳配合物的工作表明，不同的支撑金属碎片施加了明显不同的性质。本工作的目的是合成并研究一系列[M-(CC)x-M‘]n+型化合物的电子性质，其中连接基团Cx是由四个或更多碳组成的不饱和碳链，金属端帽M和M’是氧化还原活性的有机金属中心。一系列的氧化态(n=0-4)是可接近的，其中一些是稳定的、可隔离的体系。这类令人着迷的络合物的电子结构强烈依赖于M和M‘的同一性。然而，以前的工作基本上局限于第7和第8族过渡金属中心铁、Ru和Re的端帽，其中3D金属中心Fe的贡献要比Ru和Re的4d/5d中心强得多。这项工作的创新之处在于包括了一个具有第6族金属钼的有机金属端帽，它既是强给电子体，又基于4d中心-这提供了一个独特的机会来描绘端帽给电子体能力与金属过渡系列对电子结构的影响。通过引入基于钼的端帽基团可以享受的另一个优点是可以利用高分辨率的光谱手柄(EPR)通过直接的实验探针来研究电子结构，并且有可能通过控制分子构型来控制混合基团6/族8杂双金属[M-(CC)x-M‘]n+的氧化形式的电子结构。这项工作很重要，因为它将导致对不饱和全碳桥的电子结构的更好的理解，以及如何作为金属、支持配体和碳片段长度的函数来控制这一电子结构。尽管许多人谈到在未来基于分子的电子设备的分子组件设计中需要如此详细的了解，但我们的目标是全面了解这些金属稳定的碳片段的潜在化学成分，而不是依赖一个标志性的金属端盖施加的限制。

Metal-stabilised carbon chains [M-(CC)x-M]n+ have attracted increasing interest over the last 10 years, mainly due to the remarkable changes in electronic structure which accompany changes in the formal oxidation state of the compounds. While much of this work has focussed on homobimetallic examples, recent synthetic advances make heterometallic examples accessible. This is a particularly exciting development as much of the work with homometallic polycarbon complexes has shown that distinctly different properties are imposed by different supporting metal fragments.The objective of this work is to synthesise and investigate the electronic properties of a series of compounds of the type [M-(CC)x-M']n+ in which the linking group Cx is an unsaturated carbon chain of four or more carbons and the metal end-caps M and M' are redox active, organometallic centres. A range of oxidation states (n = 0-4) is accessible of which some are stable, isolable systems. The electronic structures of this fascinating class of complexes are strongly dependent upon the identity of M and M'. However previous work has been restricted essentially to end-caps of group 7 and 8 transition metal centres of iron, ruthenium and rhenium in which the 3d metal centre Fe is much more strongly donating than the 4d/5d centres of Ru and Re. The innovation in this work is to include an organometallic end-cap featuring the group 6 metal molybdenum which is both strongly electron donating and based upon a 4d centre - this provides a unique opportunity to delineate the effect of end-cap electron donor capacity vs. metal transition series upon electronic structure. Further advantages that can be enjoyed through the introduction of Mo based end-cap group are the availability of a highly resolved spectroscopic handle (EPR) with which to investigate electronic structure by a direct experimental probe and the potential to control electronic structure in oxidised forms of the mixed group 6/group 8 heterobimetallics [M-(CC)x-M']n+ by control of molecular configuration.The work is of importance because it will lead to an enhanced understanding of the electronic structure of the unsaturated all-carbon bridge, and how this can be controlled as a function of the metal, the supporting ligands and the length of the carbon fragment. Although many talk of the need for such detailed understanding in the design of molecular components for future molecular based electronics, our goal is to arrive at a full understanding of the underlying chemistry in these metal-stabilised carbon fragments, free of the restrictions imposed by the reliance on one signature metal end-cap.