Date

2001-02-01

Author

Widegren, JA
Aiken, JD
Özkar, Saim
Finke, RG

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A few years ago we developed a new kinetic method for following transition-metal nanocluster formation in which the resultant nanocluster's catalytic activity was used as a reporter reaction via the pseudoelementary step concept. This method in turn yielded insights into a new, broadly applicable mechanism of nanocluster formation under H-2 consisting of (a) slow, continuous nucleation, A --> B, followed by (b) fast autocatalytic surface growth, A + B --> 2B (A = the nanocluster precursor, [Bu4N](5)Na-3[(1,5-COD)Ir .P2W15Nb3O62], B = the resultant nanocluster's surface metal atoms), in which the nanocluster behaves as a "living metal polymer". Herein, this new kinetic method is investigated and tested further: (i) by following the Ir(0)(similar to 300) nanocluster's kinetics of formation more directly via the H-2 uptake reaction of the [Bu4N](5)Na-3[(1,5-COD)Ir .P2W15Nb3O62] precursor-does this also show an autocatalytic Hz uptake curve?; (ii) by seeing if the predicted initially small, then larger (past the induction period) sizes of the nanoclusters are verifiable directly by TEM; (iii) by testing commercial nonlinear least-squares software (Microcal's ORIGIN) in the kinetic analysis and with the goal of making the new kinetic method readily available to others; (iv) by showing when it is necessary to correct for the solvent vapor pressure, and how to do so, in the H-2 pressure-loss measurements when more volatile solvents such as acetone are used in the nanocluster formation reaction; (iv) by showing whether the new kinetic method can be successfully used in other nanocluster formation reactions of different metals and for more difficult reactions such as arene hydrogenation; and (v) by numerical integration simulations of the first 45 or so steps in the nanocluster formation reaction-does this atomically detailed mechanism show autocatalysis or not, and if so can it be fit by the A B, A + B --> 2B mechanism? Tests of each of the issues (i)-(v) are reported in the present contribution. Finally, (vi) the new kinetic method has been exploited to yield insights into higher valent metals that undergo nucleation under H-2, namely, to discover and report for the first time the significance of heterolytic hydrogenation activation, with its requirement for added base in the nanocluster formation reactions of higher valent, electrophilic metals such as Pd(II), Pt(IV), Ru(III), Rh(III), Ag(I), Au(III), Cu(II), and Ir(III).

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https://hdl.handle.net/11511/69946

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Department of Chemistry, Article