The kinetics and molecular mechanism of nucleation are investigated, in molecular detail, for a bimetallic precatalyst, formed in situ from [(1,5-COD)IrI(NCCH3)2]+, 1, and HPO42–. A neutral, phosphate-bridged species, {[(1,5-COD)IrI(NCCH3)]2(HPO4)}0, 2, is found by 1H NMR to be formed en route to the desired resting precatalyst, {[(1,5-COD)IrI(HPO4)]2}2-, 3. 1H NMR solution speciation and Signer apparatus solution molecular weight studies establish that in situ prepared 3 exists predominantly in its dimeric form. Kinetic studies reveal a first-order dependence of nucleation on the concentration of 3 and hence rule out the higher-order dependence and higher molecularity implied by classical nucleation theory. Additional kinetic studies reveal a telling, inverse, quadratic dependence on added HPO42–. The results unveil the previously unavailable insights that a simple bimetallic, Ir2 precursor is sufficient to enable low molecularity nucleation via {[(1,5-COD)IrI(NCCH3)]2(HPO4)}0, 2, as a kinetically competent intermediate en route to a Kinetically Effective Nucleus (KEN) of molecularity of just 2, Ir2. These results with {[(1,5-COD)IrI(HPO4)]2}2– in comparison to previous results with {[(1,5-COD)IrI(POM)}8– (POM = the polyoxometalate P2W15Nb3O629-) allow insights into the details of nucleation, notably that Ir2 vs Ir3 KEN are controlled by the different HPO42– and POM8– anion’s surface charge and resultant 2 vs 3 IrI(1,5-COD)+ moieties they are able to bind to each anion to achieve surface-charge neutrality of that anion. The resultant state-of-the-art nucleation results allow a total of nine insights, conclusions, and two new working hypotheses that will be summarized as part of the talk.

Nucleation kinetics and molecular mechanism in transition-metal nanoparticle formation: Intriguing, informative case of a bimetalic precursor, {[(1,5-COD)IrI(HPO4)]2}2-

2019 Fall National Meeting

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