Cationic iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]+ and [3-(MeCN)3-3,1,2-IrC2B9H11]+: Synthesis, reactivity, and bonding. Catalysis of oxidative coupling of benzoic acid with alkynes

• A general one-pot method was developed for synthesis of (arene)iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]+.
• The (arene)iridacarboranes catalyze the oxidative coupling of benzoic acid with diphenylacetylene giving isocoumarin.
• DFT calculations suggested that the selectivity of catalytic reactions is determined by the electronic properties of ligand.

(Arene)iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]+ (arene = benzene (1a), toluene (1b), o-xylene (1c), m-xylene (1d), durene (1e)) were synthesized by reaction of [(cod)IrCl]2 with Tl[Tl(η-7,8-C2B9H11)] with the subsequent treatment of the anion [3-(cod)-3,1,2-IrC2B9H11]− formed by arenes in refluxing trifluoroacetic acid. Cation 1a reacts with acetonitrile giving complex [3-(MeCN)3-3,1,2-IrC2B9H11]+ (2). Reactions of 2 with Cp– anions and arenes afford the cyclopentadienyl and arene derivatives 3-(η-C5H4R)-3,1,2-IrC2B9H11 (R = H (3a), C(O)Me (3b)) and [3-(arene)-3,1,2-IrC2B9H11]+ (arene = mesitylene (1f), [2,2]paracyclophane (1g)). The structures of 1ePF6 and 2BF4 were determined by X-ray diffraction. According to energy decomposition analysis, the metal-benzene bonding in the iridium cation 1a is stronger than in the rhodium analog [3-(η-C6H6)-3,1,2-RhC2B9H11]+ but weaker than in [(C5R5)Ir(C6H6)]2+. In the presence of Ag2CO3, iridacarboranes 1a and 2 catalyze the oxidative coupling of benzoic acid with diphenylacetylene selectively giving 3,4-diphenylisocoumarin in 40–50% yields. In contrast, the reactions catalyzed by [3,3-Cl2-4-SMe2-3,1,2-IrC2B9H10]2 and [CpIrI2]2 afford only 1,2,3,4-tetraphenylnaphthalene in 10 and 35% yields, respectively. The iridium catalyzed decarboxylation of benzoic acid was analyzed by DFT calculations.

(Arene)iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]+ were synthesized by reaction of [(cod)IrCl]2 with Tl[Tl(η-7,8-C2B9H11)] with the subsequent refluxing in trifluoroacetic acid in the presence of arenes. Their catalytic activity in the oxidative coupling of benzoic acid with alkynes is discussed.Figure optionsDownload as PowerPoint slide