Metal Alkynyl σ Complexes: Synthesis and Materials

Metal alkynyl complexes hold a fascination for synthetic chemists, structural chemists, and materials scientists alike. Harnessing the unique overlap of metal and carbon orbitals is a challenge that can be overcome in many ways and hence, there are many synthetic routes toward MCC bond‐forming reactions that utilize a wide variety of transition‐metal and alkynyl reagents. Some methods can be widely applied, while others are specific to a particular metal or compound. The linear geometry of the alkynyl unit and its π‐unsaturated character have led to metal alkynyls becoming attractive building blocks for molecular wires and polymeric organometallic materials, which can possess interesting properties, such as optical nonlinearity, luminescence, liquid crystallinity, and electrical conductivity. A unique, multifaceted approach, often combining talents from all three of the above chemical disciplines, has served as a driving force behind the intense research into the development of metal alkynyl σ complexes, the progress of which, particularly in the last ten years, is summarized in this review. The MCC structural unit, which can be used to establish a wide variety of molecular topologies (see, for example, the tris(ferrocenylalkynyl) complex and the molecular rigid‐rod polymer shown), together with the increasing importance of material properties such as electron transfer, nonlinear optical behavior, and luminescence, combine to make transition‐metal alkynyl complexes, especially as oligomers and polymers, of particular current interest.