CEST is a magnetization transfer experiment, where a narrow-band saturation pulse with frequency vRF is applied, prior to a broad band NMR detection (Figure ). By varying vRF, the CEST spectrum is recorded. In our study, we use a continuous wave (CW) saturation pulse, whose effects are detected by virtue of the reduction of the easily-detectable signal of free dissolved H2, which is reduced by the saturation of exchanging hydrides bound to one of the organometallic complexes (Figure ). In a previous paper we had described the related PANEL (PArtially NEgative Line) experiment, where the signal of hidden intermediates is indirectly detected via the partially negative hyperpolarized signal of the free hydrogen pool interacting with the complex.