Additional investigations of a new kinetic method to follow transition-metal nanocluster formation, including the discovery of heterolytic hydrogen activation in nanocluster nucleation reactions

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 conc ept. This method in turn yielded insights into a new, broadly applicable me chanism of nanocluster formation under H-2 consisting of (a) slow, continuo us 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 .P2W 15Nb3O62], B = the resultant nanocluster's surface metal atoms), in which t he nanocluster behaves as a "living metal polymer". Herein, this new kineti c method is investigated and tested further: (i) by following the Ir(0)(sim ilar 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-do es 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 commerci al nonlinear least-squares software (Microcal's ORIGIN) in the kinetic anal ysis and with the goal of making the new kinetic method readily available t o others; (iv) by showing when it is necessary to correct for the solvent v apor 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 formati on reaction; (iv) by showing whether the new kinetic method can be successf ully used in other nanocluster formation reactions of different metals and for more difficult reactions such as arene hydrogenation; and (v) by numeri cal integration simulations of the first 45 or so steps in the nanocluster formation reaction-does this atomically detailed mechanism show autocatalys is or not, and if so can it be fit by the A B, A + B --> 2B mechanism? Test s of each of the issues (i)-(v) are reported in the present contribution. F inally, (vi) the new kinetic method has been exploited to yield insights in to higher valent metals that undergo nucleation under H-2, namely, to disco ver and report for the first time the significance of heterolytic hydrogena tion activation, with its requirement for added base in the nanocluster for mation 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).