Experiments reported in Figs. and were performed in a low-pressure/vacuum 5 mm O.D. glass NMR tube equipped with a J. Young valve, filled with 400 μl of the precursor solution. Hydrogen gas was bubbled into the solution through a PTFE (polytetrafluoroethylene) capillary (1/16" O.D., 1/32" I.D.). Experiments reported in Figs. and 6b (upper spectrum) were performed in a titanium metal tube (12 mm O.D., 10 mm I.D.) filled with 2 ml of the precursor solution. Hydrogen gas was bubbled into the solution through a PEEK capillary (1/8" O.D., 1/16" I.D.).