Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl 4 Source. Localization of Homogeneous/Heterogeneous System’s Interface and Field-Emission Scanning Electron Microscopy Study Sergey S. Zalesskiy, Alexander E. Sedykh, Alexey S. Kashin, and Valentine P. Ananikov* Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow 119991, Russia * S Supporting Information ABSTRACT: Soluble gold precatalysts, aimed for homoge- neous catalysis, under certain conditions may form nano- particles, which dramatically change the mechanism and initiate different chemistry. The present study addresses the question of designing gold catalysts, taking into account possible interconversions and contamination at the homoge- neous/heterogeneous system’s interface. It was revealed that accurate localization of boundary experimental conditions for formation of molecular gold complexes in solution versus nucleation and growth of gold particles opens new opportunities for well-known gold chemistry. Within the developed concept, a series of practical procedures was created for efficient synthesis of soluble gold complexes with various phosphine ligands (R 3 P)AuCl (90-99% yield) and for preparation of different types of gold materials. The effect of the ligand on the particles growth in solution has been observed and characterized with high-resolution field-emission scanning electron microscopy (FE-SEM) study. Two unique types of nanostructured gold materials were prepared: hierarchical agglomerates and gold mirror composed of ultrafine smoothly shaped particles. 1. INTRODUCTION In recent decades, gold-catalyzed reactions have widely spread over the field of organic chemistry. 1-6 Numerous examples of gold-catalyzed reactions include nucleophilic additions, cycliza- tions, oxidative couplings, multiple bond activation processes, hydrogenations, and other fascinating transformations. 1-12 These examples show that gold catalysis tends to succeed in the utmost direction of the organic synthesis. Moreover, it is a common practice now to utilize a cascade of gold-catalyzed cyclizations to yield complex frameworks of natural compounds in one step instead of step-by-step buildup of polycyclic skeleton. 1-13 Interestingly, despite the high activity of the catalyst and tolerance to a wide range of functional groups, gold-catalyzed reactions proved to be very sensitive to the minor changes in the catalyst structure. Selected examples show that even small changes in the ligand, counterion, additives, or conditions can direct the reaction to a completely different route. 1-5 A series of recent studies have shown that fundamentally different reactions and mechanisms are accessible using soluble gold complexes and gold nanoparticles. 14,15 Heterogeneous pathways can contribute in distinct ways to activity and/or selectivity of gold-catalyzed transformations, including alter- native pathways due to decomposition of common gold salts used as catalyst precursors toward nanoparticles. 14,16 Ongoing research on transition-metal-mediated transformations has emerged the problem of identity of the active form of the catalyst in view of possible interconversion of soluble complexes and nanoparticles in the catalyst precursor and in the catalytic system in solution. 17,18 An excellent example of the gold-catalyzed transformation through the involvement of heterogeneous and homogeneous pathways and the control of leaching was published. 19 The important mechanistic tools for in situ reduction of gold catalysts 20 and for the proof of homogeneous pathway with EXAFS/XANES measurements have been successfully demonstrated. 21 A valuable insight in the gas-phase ion chemistry suggested a more detailed look at the gold clusters, where a particularly strong ligand effect may be observed. 22 So far, numerous factors have pointed out that successful implementation and development of gold catalysis in organic synthesis requires an extensive set of various gold precatalysts for rapid screening. Nowadays, these should include not only soluble complexes, but also nanoparticles of various sizes and shapes. Widely used starting materials to prepare soluble complexes represent gold(I) stabilized by a weak-coordinated ligand, such as Me 2 S(1), thiodiglycol (tdg; 2), or tetrahydrothiophene (tht; 3) (Scheme 1). However, all three of these precatalysts have noticeable drawbacks. Preparation of (Me 2 S)AuCl and (tht)- AuCl involves handling of dimethylsulfide and tetrahydrothio- Received: November 15, 2012 Published: December 31, 2012 Article pubs.acs.org/JACS © 2012 American Chemical Society 3550 dx.doi.org/10.1021/ja311258e | J. Am. Chem. Soc. 2013, 135, 3550-3559