Hydrolysis of ammonia-borane (AB) is one of the most convenient sources of H 2 under ambient conditions, but the reaction requires a good catalyst to become efficient. Here this reaction is catalyzed by bimetallic late transition-metal nanoparticles (NPs) stabilized by "click" dendrimers 1 and 2 containing respectively 27 or 81 terminal triethylene glycol termini and 9 or 27 intradendritic 1,2,3-triazole ligands. A remarkable synergy between Pt and Co in the Pt-Co/"click" dendrimer nanocatalyst is disclosed. These Pt-Co/"click" dendrimer catalysts are much more efficient for hydrolysis of AB than either "click" dendrimer-stabilized Co or Pt analogues alone. The best catalyst Pt 1 Co 1 /1 stabilized by the nona-triazole "click" dendrimer 1 achieves a TOF of 303 mol H2 •mol catal.-1 •min-1 (606 mol H2 •mol Pt-1 •min-1) at 20 ± 1°C. In the presence of NaOH, the reactivity is boosted for hydrolysis of AB catalyzed by Pt 1 Co 1 /1, and reaches a TOF value of 476.2 mol H2 •mol catal.-1 •min-1 (952.4 mol H2 •mol Pt-1 •min-1), one of the very best results obtained by comparison with the literature. The presence of a percentage of Pt as low as 25% in the CoPt nanoalloy provides a reaction rate higher than with that obtained with the pure Pt NP catalyst alone. The kinetics involves in particular a kinetic isotope effect k D /k H = 2.46 obtained for the hydrolysis reaction with D 2 O, suggesting O-H bond cleavage of water in the rate-determining step. Tandem reactions were conducted for the hydrogenation of styrene with hydrogen generated from the hydrolysis of AB. Performing this tandem reaction with D 2 O shows deuteration of the ethylbenzene products confirming O-D cleavage and H/D scrambling on the bimetallic nanoparticle surface. Finally a reaction mechanism is proposed. This dramatic synergy type should also prove useful in a number of other catalytic systems.

Production of hydrogen (H2) upon hydrolysis of inorganic hydrides potentially is a key step in green energy production. We find that visible-light irradiation of aqueous solutions of ammonia-borane (AB) or NaBH4 containing "click"-dendrimer-stabilized alloyed nanocatalysts composed of nanogold and another late transition-metal nanoparticle (LTMNP) highly enhances catalytic activity for H2 generation while also inducing alloy to Au core@M shell nanocatalyst restructuration. In terms of visible-lightinduced acceleration of H2 production from both AB and NaBH4, the Au1Ru1 alloy catalysts show the most significant light boosting effect. Au-Rh and Au-PtNPs are also remarkable with total H2 release time from AB and NaBH4 down to 1.3 min at 25 °C (AuRh), three times less than in the dark, and Co is the best earth-abundant metal alloyed with nanogold. This boosting effect is explained by the transfer of plasmon-induced hot electron from the Au atoms to the LTMNP atoms facilitating water O-H oxidative addition on the LTMNP surface, as shown by the large primary kinetic isotope effect kH/kD upon using D2O obtained for both AB and NaBH4. The second simultaneous and progressive effect of visible-light irradiation during these reactions, alloy to Au core@M shell restructuration, enhances the catalytic activity in the recycling, because, in the resulting Au core@M shell, the surface metal (such as Ru) is much more active that the original Au-containing alloy surface in dark reactions. There is no light effect on the rate of hydrogen production for the recycled nanocatalyst due to the absence of Au on the NP surface, but it is still very efficient in hydrogen release during 4 cycles, due to the initial light-induced restructuration, although it is slightly less efficient than the original nanoalloy in the presence of light.The dendritic triazole coordination on each LTMNP surface appears to play a key role in these remarkable light-induced processes.

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