Family Of Multiply Bonded Bimetallic Complexes Grows

Multiple bonds between transition-metal atoms have fascinated chemists for 50 years, ever since F. Albert Cotton’s group at MIT discovered a quadruple bond in a diruthenium complex. Synthesizing these multiply bonded complexes between like metals is now common. But such complexes involving two different metals remain rare. A research team led by Connie C. Lu of the University of Minnesota, Twin Cities, has taken a systematic look at how multiple bonding varies across a series of heterobimetallic complexes in which chromium is paired with other first-row transition metals (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja406506m). Chromium is an interesting target, Lu notes, because it is one of a few elements known to engage in more than a quadruple bond. In 2005, Philip P. Power’s group at the University of California, Davis, reported the first metal-metal quintuple bond in a dichromium complex. Lu’s team prepared Mn-Cr, Fe-Cr, Co-Cr, and Ni-Cr complexes that contain metal-metal bonds with bond orders ranging from one to five (two shown). The researchers’ electrochemical studies show that each complex undergoes several one-electron transfer processes. Thus, the heterobimetallic compounds could be useful in multielectron catalysis without requiring expensive precious metals.