Half-sandwich complexes of group 9 metals with N,Nʹ-ligands for CF3-carbenoid alkylation of N-(pyrimidin-2-yl)indole

Abstract

The complexes [CpM(N,Nʹ-ligand)Br]PF6 (M = Rh, Ir; N,Nʹ-ligand = 2,2′-bipyridyl, 1,10-phenanthroline) were synthesized by reactions of bromides [CpMBr2]n with 2,2′-bipyridyl or 1,10-phenanthroline followed by a counterion exchange. The replacement of cyclooctadiene in [CpIr(cod)I]I3 with N,Nʹ-ligands leads to complexes [CpIr(N,Nʹ-ligand)I]I3 (N,Nʹ-ligand = 2,2′-bipyridyl, 1,10-phenanthroline). The structures of [CpRh(2,2′-bipyridyl)Br]PF6, [CpIr(2,2′-bipyridyl)I]I3, and [CpIr(1,10-phenanthroline)Br]PF6 were determined by X-ray diffraction. The compounds prepared as well as the related the tris(pyrazolyl)borate derivatives [CpCoTp]PF6 and [Cp*MTp]PF6 (M = Rh, Ir) efficiently catalyze the alkylation of N-(pyrimidin-2-yl)indole with methyl 3,3,3-trifluoro-2-diazopropionate to selectively introduce the CF3 and carboxylate functions at the C3 position of the indole moiety. In contrast, the tris(pyrazolyl)borate cobalt complex [Cp*CoTp]PF6 predominantly provides the alkylation at the C2 position.