Catalytically Triggered Energy Release from Strained Organic Molecules: The Surface Chemistry of Quadricyclane and Norbornadiene on Pt(111)

Abstract

We have investigated the surface chemistry of the polycyclic valence-isomer pair norbornadiene (NBD) and quadricyclane (QC) on Pt(111). The NBD/QC system is considered to be a prototype for energy storage in strained organic compounds. By using a multimethod approach, including UV photoelectron, high-resolution X-ray photoelectron, and IR reflection-absorption spectroscopic analysis and DFT calculations, we could unambiguously identify and differentiate between the two molecules in the multilayer phase, which implies that the energy-loaded QC molecule is stable in this state. Upon adsorption in the (sub)monolayer regime, the different spectroscopies yielded identical spectra for NBD and QC at 125 and 160 K, when multilayer desorption takes place. This behavior is explained by a rapid cycloreversion of QC to NBD upon contact with the Pt surface. The NBD adsorbs in a η :η geometry with an agostic Pt-H interaction of the bridgehead CH subunit and the surface. Strong spectral changes are observed between 190 and 220 K because the hydrogen atom that forms the agostic bond is broke. This reaction yields a norbornadienyl intermediate species that is stable up to approximately 380 K. At higher temperatures, the molecule dehydrogenates and decomposes into smaller carbonaceous fragments.

Norbornadiene functionalized triaza-triangulenium and trioxa­-triangelium platforms

“…The decomposition of desorbed norbornadiene on Pt(111) was proven by MUETTERTIES and co-workes at around 500 K. [18] The catalyzed cycloreversion of unsubstituted quadricyclane to norbornadiene was investigated on Pt(111) and Ni(111) surfaces at low temperatures. [2,19] The cycloreversion starts at 175 K. Furthermore at 190 K to 220 K the decomposition to a norbornadienyl intermediate was detected 2 which further dehydrogenates and decomposes at 380 K into carbonaceous fragments which confirms the results of MUETTERTIES. [2,18] Recently, we discovered that the thermochemically forbidden cis-trans isomerization of azobenzenes can be efficiently catalyzed by a completely different mechanism on bulk gold.…”

“…[1] Photoisomerization reactions in principle allow the direct conversion of solar energy to chemical energy if the photoproduct has a higher strain energy than the reactant. [2] The stored energy is released on demand by catalytical back-isomerization. One of the most promising molecular solar-thermal energy storage systems is norbornadiene (NBD) which upon irradiation reacts through triplet state [3,4] by an intramolecular [2+2] cycloaddition to the metastable, energy-rich quadricyclane (QC), [5][6][7][8] first described half a century ago.…”

“…[17] For practical solar energy storage applications, it is essential to use heterogenic catalysis (immobilized catalysts) because the reaction can be controlled by addition and removal of the catalyst. [2] Besides transition metal complexes, metal surfaces were found to be effective. The decomposition of desorbed norbornadiene on Pt(111) was proven by MUETTERTIES and co-workes at around 500 K. [18] The catalyzed cycloreversion of unsubstituted quadricyclane to norbornadiene was investigated on Pt(111) and Ni(111) surfaces at low temperatures.…”

Combining Theory and Experiment to Characterize the Voltammetric Behavior of Nickel Anodes in the Simons Process

“…Quantum‐chemical calculations may provide insights to atomistic‐scale phenomena for which measurements are either inconceivable or highly challenging. Density functional theory (DFT) is applied widely to surface chemistry problems . In recent years, improved methods have emerged for DFT calculations on electrochemical systems with many studies applying the computational hydrogen electrode (CHE) formalism .…”

Multifactor theoretical modeling of solar thermal fuels built on azobenzene and norbornadiene scaffolds

“…Finally, the energy barrier for the reverse isomerization must result in a half-life for the metastable conguration that lasts long enough for reliable storage, yet not be great enough to prohibit efficient reclamation of the chemical energy on demand by triggering the reverse isomerization either thermally or catalytically. 14 Two classes of STF candidates that have received considerable attention in the literature are the azobenzenes [15][16][17][18] and the norbornadiene-quadricyclane (NBD-QC) system, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] shown in Fig. 2.…”