The coordination of sigma bonding electron density to a Lewis acid was for some time largely the domain of boron hydride chemistry. Subsequently it was found that C-H bonds could undergo intramolecular coordination to metal centers, forming what are now known as "agostic bonds" and "agostic complexes". Thereafter, even the H-H bond in molecular hydrogen was found to be capable of coordination, leading to what are commonly referred to as "sigma complexes". Eventually, coordination by much more shielded C-C bonds was estab-[a] US Navy, Naval inorganic chemistry from the University of Utah in 2005, studying with Professor Richard D. Ernst. His graduate studies were focused on the synthesis and characterization of early-transition-metal organometallic cage structures and metallacyclobutanes. Many of the compounds studied in his research exhibited unique C-C agostic bonding interactions. His current areas of interest include catalysis, advanced biofuels, high-temperature thermosetting resins, and green chemistry. Richard D. Ernst is a Professor of Chemistry at the University of Utah. He received his B.S. degree in chemistry from the University of California in Berkeley in 1973 and his Ph.D. degree in inorganic chemistry from Northwestern University in 1977. His major areas of interest include organometallic chemistry, particularly of metal-pentadienyl compounds, coordination chemistry, and catalysis of the Fischer-Tropsch and Water Gas Shift reactions.