Origins of Batch-to-Batch Variation: Organoindium Reagents from Indium Metal

Abstract

Yields of organoindium reagents synthesized from indium metal were previously reported to be highly dependent on metal batch and supplier due to the presence or absence of anticaking agent. Here, single-particle fluorescence microscopy established that MgO, an additive in some batches nominally for anticaking, significantly increased the physisorption of small-molecule organics onto the surface of the resulting MgO-coated indium metal particles. An inert and relatively nonpolar boron dipyrromethene fluorophore with a hydrocarbon tail provided a sensitive probe for this surface physisorption. SEM images revealed markedly different surface properties of indium particles either with or without MgO, consistent with their different physisorption properties observed by fluorescence microscopy. We further documented incomplete commercial bottle labeling regarding the presence and composition of this anticaking agent, both within our laboratory and previously in the literature, which may complicate reproducibility between laboratories. Trimethylsilyl chloride pretreatment, a step employed in a subset of reported synthetic procedures, removed the anticaking agent and produced particles with similar physisorption properties as commercial batches of indium powder distributed without the anticaking agent. These data indicate the possibility of an additional substrate/catalyst physisorption mechanism by which the anticaking agent may be influencing synthetic procedures that generate organoindium reagents from indium metal, in addition to simple anticaking.

Figure 1.

a. Reactions with yields dependent on indium batch. b. Acros indium bottle label stating 99.999% purity (no mention of anticaking agent additive) and of Aldrich indium stating 99.99% purity.

Figure 2.

a. Preparation procedure for fluorescence microscopy imaging. b. Chemical structure of imaging agent 1. c–e. Fluorescence microscopy images of each representative particle of Aldrich indium and both TMSCl pretreated and untreated Acros indium. d–h. SEM images of each representative particle of Aldrich indium and both TMSCl and untreated Acros indium.

Figure 3.

Bright fluorescent microscopy image of a representative MgO sample, showing high physisorption of 1.

Figure 4.

a. Schematic summary of fluorescence microscopy experimental results. b. Visual representation of organic substrate and catalyst physisorption to indium vs. no physisorption.