This critical review provides a systematic classification of the synthetic routes to planar-chiral five-membered metallacycles into several routes, namely C–H bond activation, oxidative addition, transmetallation and optical resolution. As a characteristic of these bulk compounds is that they are synthesized as binary mixtures of enantiomers in proportions varying from the racemate to enantiopure, a review of absolute-configuration determination of the title planar-chiral scalemates is presented. This review is of interest to organic and organometallic synthetic chemists involved in asymmetric synthesis (97 references).

Implementation of organic transistors in low-end, large-volume microelectronics depends, greatly, on the level of performance that can be achieved, but also on the compatibility of the technology with low-cost processing methodologies. Here we examine the suitability of a family of solution-processable zwitterionic molecules, so-called squarilium dyes, for the fabrication of organic ambipolar transistors and their application in (opto)electronic circuits. Ambipolar organic semiconductors and transistors are interesting because they could deliver performance characteristics (i.e. noise margins and signal gain) similar to that of complementary logic, but with the fabrication simplicity associated with unipolar logic (i.e. single semiconductor material and single type of metal electrodes). By designing squarilium dyes with appropriate electrochemical characteristics we demonstrate single-layer organic transistors that exhibit ambipolar charge transport with balanced electron and hole mobilities. By integrating a number of these ambipolar transistors we are also able to demonstrate complementary-like voltage inverters with wide noise margin and high signal gain. Another interesting feature of the squarilium dyes studied here is their strong absorption in the near-infrared (NIR) region of the electromagnetic spectrum. By exploring this interesting property we are able to demonstrate NIR light-sensing ambipolar organic transistors with promising operating characteristics.