Posted on behalf of Ian Mallov, web writer for Dalton Transactions
One of chemistry’s small, fascinating deviations from scientific expectation is the tendency of a few types of metal atoms to attract instead of repel each other when they are formally positively charged. This tendency is known for several of the lower late transition metals, including mercury, platinum and palladium. But the attraction is strongest in that most innately alluring of metals, gold, and the concept has its own Latinized term: aurophilicity.
Fernández and co-workers report unique examples of these interactions between positively-charged gold atoms. Gold(I) complexes bound to carbene ligands are a class of compounds of which there are many known and useful variants. Though expensive, they’ve been used with considerable success to catalyze transformations of organic molecules. In their paper, these chemists use Fischer-type carbenes, excellent at accepting electron density from the metal to which they bind, but rarely used in gold chemistry.
X-ray diffraction studies of their synthesized (via transmetallation from tungsten(0) analogues) gold compounds in the solid state, together with theoretical studies by Density Functional Theory computations affirm the attractions between gold atoms of adjacent molecules. They also prepared a ferrocene-bridged dinuclear gold complex, utilizing the ferrocene bridge as a rigid, “semi-support” for the gold atoms (picture two flexible branches at opposite ends of a solid trunk) and the solid-state and calculated structures show the gold atoms, well out on these “branches,” bending toward one another and at a distance even closer than the gold atoms in the “unsupported” complexes.
There is even an explanation offered: using Second-Order Perturbation Theory computations, it appears that electron density is donated from a doubly-occupied d-orbital of one gold atom into an empty p-orbital of the adjacent atom, and the energies associated with this interaction are indeed significant.
Find out more from the paper:
Fischer-type gold(I) carbene complexes stabilized by aurophilic interactions
Daniela I. Bezuidenhout, Belinda van der Westhuizen, Amos J. Rosenthal, Michael Wörle, David C. Liles and Israel Fernández
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C3DT52961D
Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.
