2-Indolylphosphines, a New Class of Tunable Ligands:  Their Synthesis, Facile Derivatization, and Coordination to Palladium(II)

The generation of new metal complexes with potentially interesting properties provides the motivation for designing novel polydentate bridging ligands. Herein we report the syntheses of tertiary indolylphenylphosphines L, where L = diphenyl(3-methyl-2-indolyl)phosphine (P(C6H5)2(C9H8N), 1), phenylbis(3-methyl-2-indolyl)phosphine (P(C6H5)(C9H8N)2, 2), and bis(1H-3-indolyl)methane-(2,12)-phenylphosphine (P(C6H5)(C17H12N2), 3). Ligands 13 were functionalized at the indolyl nitrogen with a variety of both electron-withdrawing and electron-donating groups. The solid-state structures of 1, 2, and N-functionalized indolylphosphines diphenyl(3-methyl-1-benzyl-2-indolyl)phosphine (P(C6H5)2(C9H7N(CH2C6H5)), N-Bz-1) and bis[1-(CH2C6F5)-3-indolyl]methane-(2,12)-phenylphosphine (P(C6H5)(C17H10N2[CH2C6F5]2), (N-F5Bz)2-3), are reported. The reaction of ligands 13 with 1 equiv of Pd(COD)Cl2 led to the formation of Pd(II) complexes of the type [Pd(L)Cl(μ-Cl)]2 (4, L = 1; 5, L = 2; 6, L = 3). The products were characterized by 1H, 13C, and 31P NMR spectroscopy, mass spectrometry, and elemental analysis. X-ray crystallography established the dimeric structure of the products and confirmed the ability of the ligands to serve, in the absence of base, as monodentate P-donors in reaction with a transition metal. The indolyl NH groups of the complexes 46 demonstrate a marked propensity for hydrogen bonding in the solid state.