Here 12 ˆẑz II describes the longitudinal and 1 2 1 2 ˆˆˆx x y y I I I I  the transversal spin order. Immediately after the parahydrogen addition to the complex, the spins are still in the singlet spin state, however, they start evolving under the nuclear spin Hamiltonian corresponding to the spin system of the complex. In complexes forming typical AX-spin systems with HH J  , the transversal components start to oscillate. Combined with the distribution of complexes' formation in time (as is natural for chemical reactions), this causes an efficient decay of the transversal components. Furthermore, because the bound hydrogen is in constant exchange with the free hydrogen pool, these complexes provide an efficient pathway of decoherence not only for the bound, but also for the free hydrogen species. The latter can be devastating for SABRE, as the concentration of the SABRE active species responsible for polarization transfer is proportional to the concentration of free parahydrogen, the source of spin order in the hyperpolarization build-up process. Based on this reasoning, we investigated whether it is possible to reduce the amount of singlet-triplet leakage by chemically selecting which intermediates are formed. As the singlet state is not directly observable in NMR experiments, we employed OPSY detection, which selectively detects the signal arising from pH2 in an inequivalent complex such as 2 (Figure )). In addition, a spin-locking pulse was applied to further reduce the amount of singlet-triplet leakage by enforcing the same resonance frequency for both dihydride spins of 2 and mitigating weak inequivalencies induced by indirect couplings to other spins.