2-indolylphosphines, a new class of tunable ligands: Their synthesis, facile derivatization, and coordination to palladium(II)

Article abstract of DOI:10.1021/om0401004

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(C₆H ₅)₂(C₉H₈N), 1), phenylbis(3-methyl-2-indolyl)phosphine (P(C₆H₅)(C ₉H₈N)₂, 2), and bis(1H-3-indolyl)methane-(2,12)-phenylphosphine(P(C₆H ₅)(C₁₇H₁₂N₂, 3). Ligands 1-3 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(C₆H ₅)₂(C₉H₇N(CH₂C ₆H₅)), N-Bz-1) and bis[1-{CH₂C ₆F₅)-3-indolyl]methane-(2,12)-phenylphospnine (P(C ₆H₅)(C₁₇H₁₀N₂[CH ₂C₆F₅]₂), (N-F₅Bz) ₂-3), are reported. The reaction of ligands 1-3 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 4-6 demonstrate a marked propensity for hydrogen bonding in the solid state.