Indium triaryls

The Pd-catalyzed cross-coupling reaction of organoindium compounds was first reported in 1999.[4 ] The reaction was applied to triaryl-, trialkenyl- and trialkynylindiums, which coupled with aryl iodides, aryl triflates, or alkenyl triflates in high yields (Scheme 41) It is noteworthy that all of the organic groups on indium can participate in the coupling reaction. 

For over 70years, one of the most convenient methods used for the preparation of triaryl and trialkyl indium compounds has been the direct reaction of indium metal with diorganomercury compounds [5,6]. The method is, however, quite time consuming due to the general unreactive nature of indium metal. In some instances, reaction times of a week or more are required to obtain modest yields [5,7]. Of greater concern, the reaction generates mercury. We reported a new procedure for the rapid preparation of triaryl and trialkyl indium compounds in essentially quantitative yields [9]. 

The high degree of reactivity can be seen by comparing the literature preparation of these indium compounds. For example, Dennis prepared (CH3)3ln from indium metal and (CH3)2Hg by heating at 100°C for 8 days, and no yield was reported. However, when (CH3)2Hg was allowed to react with the activated indium metal, the reaction reached 100% yields after only 3 h at 100°C. Similarly, the preparation of the triaryl indium compounds is greatly facilitated by using the activated indium metal, and the yields are essentially quantitative. 

Triaryl indium, trialkenyl indium, dichloroaryl indium, and tetraorganoindates can be coupled with good success. Since alkenyl indium compounds are accessible from alkynes and the cross-coupling of the indium intermediates proceeds smoothly, indium chemistry has become an interesting alternative to other metals. 

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