New ligands for the iridium-catalyzed C(sp3)−H borylation of aliphatic compounds were established. In sharp contrast to 6-methyl-2,2′-bipyridine and 6-isobutyl-2,2′-bipyridine, 2,2′-bipyridine and 1,10-phenanthroline derivatives bearing a hydrosilylmethyl group (which would give a thermally stable NNSi pincer complex) served as suitable ligands for the reaction. Among them, a phenanthroline-based NNSi pincer ligand was shown to be an excellent ligand, and various aliphatic compounds were efficiently converted to the corresponding borylated products using the Ir/NNSi pincer catalyst system. The NNSi pincer ligand showed unique selectivity and enabled the iridium-catalyzed C(sp3)−H borylation using pinacolborane [H−B(pin)] instead of B2(pin)2. The formation of an iridium complex bearing a quinoline-based NNSi pincer ligand from [IrCl(cod)]2 was observed, and the catalytic activity of the complex was demonstrated.
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