Reaction mechanism governing formation of 1,3-bis(diphenylphosphino)propane-protected gold nanoclusters.

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TitleReaction mechanism governing formation of 1,3-bis(diphenylphosphino)propane-protected gold nanoclusters.
Publication TypeJournal Article
Year of Publication2011
AuthorsHudgens, JW, Pettibone, JM, Senftle, TP, Bratton, RN
JournalInorg Chem
Volume50
Issue20
Pagination10178-89
Date Published2011 Oct 17
ISSN1520-510X
KeywordsBoranes, Borohydrides, Electrons, Gold, Ligands, Metal Nanoparticles, Methanol, Phosphines, Propane, Spectrometry, Mass, Electrospray Ionization, Spectrophotometry, Ultraviolet
Abstract

This report outlines the determination of a reaction mechanism that can be manipulated to develop directed syntheses of gold monolayer-protected clusters (MPCs) prepared by reduction of solutions containing 1,3-bis(diphenylphosphino)propane (L(3)) ligand and Au(PPh(3))Cl. Nanocluster synthesis was initiated by reduction of two-coordinate phosphine-ligated [Au(I)LL'](+) complexes (L, L' = PPh(3), L(3)), resulting in free radical complexes. The [Au(0)LL'](•) free radicals nucleated, forming a broad size distribution of ligated clusters. Timed UV-vis spectroscopy and electrospray ionization mass spectrometry monitored the ligated Au(x), 6 ≤ x ≤ 13, clusters, which comprise reaction intermediates and final products. By employing different solvents and reducing agents, reaction conditions were varied to highlight the largest portion of the reaction mechanism. We identified several solution-phase reaction classes, including dissolution of the gold precursor, reduction, continuous nucleation/core growth, ligand exchange, ion-molecule reactions, and etching of colloids and larger clusters. Simple theories can account for the reaction intermediates and final products. The initial distribution of the nucleation products contains mainly neutral clusters. However, the rate of reduction controls the amount of reaction overlap occurring in the system, allowing a clear distinction between reduction/nucleation and subsequent solution-phase processing. During solution-phase processing, the complexes undergo core etching and core growth reactions, including reactions that convert neutral clusters to cations, in a cyclic process that promotes formation of stable clusters of specific metal nuclearity. These processes comprise "size-selective" processing that can narrow a broad distribution into specific nuclearities, enabling development of tunable syntheses.

DOI10.1021/ic2018506
Alternate JournalInorg Chem
PubMed ID21928777