Molecules made of two redox-active metal atoms connected by triple-bonded carbon bridges have been investigated as molecular wires. But the longer the bridge, the more unstable these molecules tend to become, to the point that they decompose quickly at room temperature to a useless mishmash of products. Claude Lapinte of CNRS-University of Rennes 1, in France, and coworkers have now discovered a diruthenium complex that instead selectively undergoes a radical cyclization reaction in which two of the units form a stable dimer (Organometallics 2013, DOI: 10.1021/om4003768). The electronically delocalized dimer consists of four metal atoms attached to a cyclobutadiene core (shown). The asymmetric selectivity of the reaction seems to come from a tension between steric and electronic control, the researchers note. Bulky ligands on the ruthenium atoms make the carbons at the center of the chain most accessible for dimerization, but electronic factors favor reaction at the carbons closest to the rutheniums. By understanding and manipulating this selectivity, chemists should be able to use the resulting cyclobutenes as carbon building blocks for synthesizing materials akin to graphene and fullerenes and for making nanoelectronic components, says organometallic chemist Tong Ren of Purdue University.