Use of the new ligand P(CH2CH2PCy2)3 in the synthesis of dihydrogen complexes of iron(II) and ruthenium(II)

Article abstract of DOI:10.1021/om00027a046

The novel bulky and basic tetradentate ligand P(CH₂CH₂PCy₂)₃ (PP₃Cy) is synthesized by the LiN(i-Pr)₂-catalyzed addition reaction of dicyclohexylphosphine (HPCy₂) to P(CH=CH₂)₃. Treatment of RuCl₂(PPH₃)₃ with PP₃Cy produces the five-coordinate square-pyramidal complex [RuCl(PP₃Cy)]Cl, which is converted into [RuCl(PP₃Cy)]BPh₄ when treated with NaBPh₄. Similarly, FeCl₂ reacts with PP₃Cy to give [FeCl(PP₃Cy)]Cl. The structure of the tetraphenylborate salt [FeCl(PP₃Cy)]BPh₄ is trigonal bipyramidal around Fe(II); crystals are monoclinic, space group P2₁/c, with a = 12.699(4) ?, b = 29.046(16) ?, c = 17.026(7) ?, β = 103.14(3)°, and V = 6116(5) ?³ for Z = 4; R = 0.065. Reaction of [RuCl(PP₃Cy)]Cl with excess NaBH₄ in THF yields mer-RuH(η²-BH₄)(η³-PP ₃Cy·BH₃), where the tetraphosphine is bound via three P atoms to ruthenium and the BH₃ is bound to a dangling terminal PCy₂ group of the tetraphosphine. The monohydride complex RuHCl(PP₃Cy) is obtained from the reaction of [RuCl(PP₃Cy)]Cl with excess NaOMe in refluxing THF. The η²-dihydrogen complex [RuH(η²-H₂)(PP₃Cy)]BPh₄ is synthesized by treating [RuCl(PP₃Cy)]BPh₄ with 1 equiv of NaBH₄ under an atmosphere of dihydrogen. The analogous iron complex is also described. The nonclassical structures of [MH(η²-H₂)(PP₃Cy)]BPh₄ (M = Fe, Ru) are established by ¹H, ³¹P, and T₁ NMR measurements and the observation of a ¹J(HD) coupling constant of 28 Hz in the isotopomer [RuD(HD)(PP₃-Cy)]⁺. Despite the steric bulk of the ligand, the complexes adopt an octahedral geometry, [MH(H₂)(PP₃Cy)]⁺, instead of a trigonal-bipyramidal ligand geometry with an H₃ ligand.