Carbene Stabilization of Highly Reactive Molecules

The Periodic Table boasts only seven elements—hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine—that unambiguously exist as homonuclear diatomic molecules in the standard state. Of these, the three lightest (hydrogen, nitrogen, and oxygen) are both biologically relevant and are critical in a number of essential industrial chemical transformations. Thus, the activation of stable diatomic such molecules represent a fundamental strategy to utilize the chemical energy in these simple molecules in an effort to construct more complex molecular systems. In addition, there are also highly reactive diatomic main group molecules such as Si2, P2, and As2 that are typically detectable as gaseous species at very high temperatures or studied at low temperatures using matrix isolation techniques. In an attempt to explore the possibly fascinating, but largely unexplored chemistry, we pioneered the “carbene-stabilization strategy”.

This is a relatively straightforward synthetic procedure: A sterically demanding N-Heterocyclic carbene is allowed to react with a compound such as BBr3, SiCl4, or PCl3, resulting in a Lewis Acid-Base complex. This Lewis Acid-Base complex is then reduced with potassium graphite, resulting in a complex that contains a multiple bond between the two main group elements.