Abstract
We demonstrate that the transient intermediate structure, which is too fast for traditional techniques, e.g. NMR or X-ray diffraction, to resolve in a thermally driven reaction can be determined in situ with the vibrational cross-angle method. The principle of the method illustrated in the work is general for other organic reactions and the method is expected to bring profound impacts for the studies of chemical reactions. The reaction mechanism of a well-defined catalytic system with performance to generate H
2
from formic acid is elucidated.
The molecular structure of a catalytically active key intermediate is determined in solution by employing 2D IR spectroscopy measuring vibrational cross-angles. The formate intermediate (2) in the formic acid dehydrogenation reaction catalyzed by a phosphorus–nitrogen PN
3
P–Ru catalyst is elucidated. Our spectroscopic studies show that the complex features a formate ion directly attached to the Ru center as a ligand, and a proton added to the imine arm of the dearomatized PN
3
P* ligand. During the catalytic process, the imine arms are not only reversibly protonated and deprotonated, but also interacting with the protic substrate molecules, effectively serving as the local proton buffer to offer remarkable stability with a turnover number (TON) over one million.